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College Physics

Problems & Exercises

College PhysicsProblems & Exercises
  1. Preface
  2. 1 Introduction: The Nature of Science and Physics
    1. Introduction to Science and the Realm of Physics, Physical Quantities, and Units
    2. 1.1 Physics: An Introduction
    3. 1.2 Physical Quantities and Units
    4. 1.3 Accuracy, Precision, and Significant Figures
    5. 1.4 Approximation
    6. Glossary
    7. Section Summary
    8. Conceptual Questions
    9. Problems & Exercises
  3. 2 Kinematics
    1. Introduction to One-Dimensional Kinematics
    2. 2.1 Displacement
    3. 2.2 Vectors, Scalars, and Coordinate Systems
    4. 2.3 Time, Velocity, and Speed
    5. 2.4 Acceleration
    6. 2.5 Motion Equations for Constant Acceleration in One Dimension
    7. 2.6 Problem-Solving Basics for One-Dimensional Kinematics
    8. 2.7 Falling Objects
    9. 2.8 Graphical Analysis of One-Dimensional Motion
    10. Glossary
    11. Section Summary
    12. Conceptual Questions
    13. Problems & Exercises
  4. 3 Two-Dimensional Kinematics
    1. Introduction to Two-Dimensional Kinematics
    2. 3.1 Kinematics in Two Dimensions: An Introduction
    3. 3.2 Vector Addition and Subtraction: Graphical Methods
    4. 3.3 Vector Addition and Subtraction: Analytical Methods
    5. 3.4 Projectile Motion
    6. 3.5 Addition of Velocities
    7. Glossary
    8. Section Summary
    9. Conceptual Questions
    10. Problems & Exercises
  5. 4 Dynamics: Force and Newton's Laws of Motion
    1. Introduction to Dynamics: Newton’s Laws of Motion
    2. 4.1 Development of Force Concept
    3. 4.2 Newton’s First Law of Motion: Inertia
    4. 4.3 Newton’s Second Law of Motion: Concept of a System
    5. 4.4 Newton’s Third Law of Motion: Symmetry in Forces
    6. 4.5 Normal, Tension, and Other Examples of Forces
    7. 4.6 Problem-Solving Strategies
    8. 4.7 Further Applications of Newton’s Laws of Motion
    9. 4.8 Extended Topic: The Four Basic Forces—An Introduction
    10. Glossary
    11. Section Summary
    12. Conceptual Questions
    13. Problems & Exercises
  6. 5 Further Applications of Newton's Laws: Friction, Drag, and Elasticity
    1. Introduction: Further Applications of Newton’s Laws
    2. 5.1 Friction
    3. 5.2 Drag Forces
    4. 5.3 Elasticity: Stress and Strain
    5. Glossary
    6. Section Summary
    7. Conceptual Questions
    8. Problems & Exercises
  7. 6 Uniform Circular Motion and Gravitation
    1. Introduction to Uniform Circular Motion and Gravitation
    2. 6.1 Rotation Angle and Angular Velocity
    3. 6.2 Centripetal Acceleration
    4. 6.3 Centripetal Force
    5. 6.4 Fictitious Forces and Non-inertial Frames: The Coriolis Force
    6. 6.5 Newton’s Universal Law of Gravitation
    7. 6.6 Satellites and Kepler’s Laws: An Argument for Simplicity
    8. Glossary
    9. Section Summary
    10. Conceptual Questions
    11. Problems & Exercises
  8. 7 Work, Energy, and Energy Resources
    1. Introduction to Work, Energy, and Energy Resources
    2. 7.1 Work: The Scientific Definition
    3. 7.2 Kinetic Energy and the Work-Energy Theorem
    4. 7.3 Gravitational Potential Energy
    5. 7.4 Conservative Forces and Potential Energy
    6. 7.5 Nonconservative Forces
    7. 7.6 Conservation of Energy
    8. 7.7 Power
    9. 7.8 Work, Energy, and Power in Humans
    10. 7.9 World Energy Use
    11. Glossary
    12. Section Summary
    13. Conceptual Questions
    14. Problems & Exercises
  9. 8 Linear Momentum and Collisions
    1. Introduction to Linear Momentum and Collisions
    2. 8.1 Linear Momentum and Force
    3. 8.2 Impulse
    4. 8.3 Conservation of Momentum
    5. 8.4 Elastic Collisions in One Dimension
    6. 8.5 Inelastic Collisions in One Dimension
    7. 8.6 Collisions of Point Masses in Two Dimensions
    8. 8.7 Introduction to Rocket Propulsion
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  10. 9 Statics and Torque
    1. Introduction to Statics and Torque
    2. 9.1 The First Condition for Equilibrium
    3. 9.2 The Second Condition for Equilibrium
    4. 9.3 Stability
    5. 9.4 Applications of Statics, Including Problem-Solving Strategies
    6. 9.5 Simple Machines
    7. 9.6 Forces and Torques in Muscles and Joints
    8. Glossary
    9. Section Summary
    10. Conceptual Questions
    11. Problems & Exercises
  11. 10 Rotational Motion and Angular Momentum
    1. Introduction to Rotational Motion and Angular Momentum
    2. 10.1 Angular Acceleration
    3. 10.2 Kinematics of Rotational Motion
    4. 10.3 Dynamics of Rotational Motion: Rotational Inertia
    5. 10.4 Rotational Kinetic Energy: Work and Energy Revisited
    6. 10.5 Angular Momentum and Its Conservation
    7. 10.6 Collisions of Extended Bodies in Two Dimensions
    8. 10.7 Gyroscopic Effects: Vector Aspects of Angular Momentum
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  12. 11 Fluid Statics
    1. Introduction to Fluid Statics
    2. 11.1 What Is a Fluid?
    3. 11.2 Density
    4. 11.3 Pressure
    5. 11.4 Variation of Pressure with Depth in a Fluid
    6. 11.5 Pascal’s Principle
    7. 11.6 Gauge Pressure, Absolute Pressure, and Pressure Measurement
    8. 11.7 Archimedes’ Principle
    9. 11.8 Cohesion and Adhesion in Liquids: Surface Tension and Capillary Action
    10. 11.9 Pressures in the Body
    11. Glossary
    12. Section Summary
    13. Conceptual Questions
    14. Problems & Exercises
  13. 12 Fluid Dynamics and Its Biological and Medical Applications
    1. Introduction to Fluid Dynamics and Its Biological and Medical Applications
    2. 12.1 Flow Rate and Its Relation to Velocity
    3. 12.2 Bernoulli’s Equation
    4. 12.3 The Most General Applications of Bernoulli’s Equation
    5. 12.4 Viscosity and Laminar Flow; Poiseuille’s Law
    6. 12.5 The Onset of Turbulence
    7. 12.6 Motion of an Object in a Viscous Fluid
    8. 12.7 Molecular Transport Phenomena: Diffusion, Osmosis, and Related Processes
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  14. 13 Temperature, Kinetic Theory, and the Gas Laws
    1. Introduction to Temperature, Kinetic Theory, and the Gas Laws
    2. 13.1 Temperature
    3. 13.2 Thermal Expansion of Solids and Liquids
    4. 13.3 The Ideal Gas Law
    5. 13.4 Kinetic Theory: Atomic and Molecular Explanation of Pressure and Temperature
    6. 13.5 Phase Changes
    7. 13.6 Humidity, Evaporation, and Boiling
    8. Glossary
    9. Section Summary
    10. Conceptual Questions
    11. Problems & Exercises
  15. 14 Heat and Heat Transfer Methods
    1. Introduction to Heat and Heat Transfer Methods
    2. 14.1 Heat
    3. 14.2 Temperature Change and Heat Capacity
    4. 14.3 Phase Change and Latent Heat
    5. 14.4 Heat Transfer Methods
    6. 14.5 Conduction
    7. 14.6 Convection
    8. 14.7 Radiation
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  16. 15 Thermodynamics
    1. Introduction to Thermodynamics
    2. 15.1 The First Law of Thermodynamics
    3. 15.2 The First Law of Thermodynamics and Some Simple Processes
    4. 15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency
    5. 15.4 Carnot’s Perfect Heat Engine: The Second Law of Thermodynamics Restated
    6. 15.5 Applications of Thermodynamics: Heat Pumps and Refrigerators
    7. 15.6 Entropy and the Second Law of Thermodynamics: Disorder and the Unavailability of Energy
    8. 15.7 Statistical Interpretation of Entropy and the Second Law of Thermodynamics: The Underlying Explanation
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  17. 16 Oscillatory Motion and Waves
    1. Introduction to Oscillatory Motion and Waves
    2. 16.1 Hooke’s Law: Stress and Strain Revisited
    3. 16.2 Period and Frequency in Oscillations
    4. 16.3 Simple Harmonic Motion: A Special Periodic Motion
    5. 16.4 The Simple Pendulum
    6. 16.5 Energy and the Simple Harmonic Oscillator
    7. 16.6 Uniform Circular Motion and Simple Harmonic Motion
    8. 16.7 Damped Harmonic Motion
    9. 16.8 Forced Oscillations and Resonance
    10. 16.9 Waves
    11. 16.10 Superposition and Interference
    12. 16.11 Energy in Waves: Intensity
    13. Glossary
    14. Section Summary
    15. Conceptual Questions
    16. Problems & Exercises
  18. 17 Physics of Hearing
    1. Introduction to the Physics of Hearing
    2. 17.1 Sound
    3. 17.2 Speed of Sound, Frequency, and Wavelength
    4. 17.3 Sound Intensity and Sound Level
    5. 17.4 Doppler Effect and Sonic Booms
    6. 17.5 Sound Interference and Resonance: Standing Waves in Air Columns
    7. 17.6 Hearing
    8. 17.7 Ultrasound
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  19. 18 Electric Charge and Electric Field
    1. Introduction to Electric Charge and Electric Field
    2. 18.1 Static Electricity and Charge: Conservation of Charge
    3. 18.2 Conductors and Insulators
    4. 18.3 Coulomb’s Law
    5. 18.4 Electric Field: Concept of a Field Revisited
    6. 18.5 Electric Field Lines: Multiple Charges
    7. 18.6 Electric Forces in Biology
    8. 18.7 Conductors and Electric Fields in Static Equilibrium
    9. 18.8 Applications of Electrostatics
    10. Glossary
    11. Section Summary
    12. Conceptual Questions
    13. Problems & Exercises
  20. 19 Electric Potential and Electric Field
    1. Introduction to Electric Potential and Electric Energy
    2. 19.1 Electric Potential Energy: Potential Difference
    3. 19.2 Electric Potential in a Uniform Electric Field
    4. 19.3 Electrical Potential Due to a Point Charge
    5. 19.4 Equipotential Lines
    6. 19.5 Capacitors and Dielectrics
    7. 19.6 Capacitors in Series and Parallel
    8. 19.7 Energy Stored in Capacitors
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  21. 20 Electric Current, Resistance, and Ohm's Law
    1. Introduction to Electric Current, Resistance, and Ohm's Law
    2. 20.1 Current
    3. 20.2 Ohm’s Law: Resistance and Simple Circuits
    4. 20.3 Resistance and Resistivity
    5. 20.4 Electric Power and Energy
    6. 20.5 Alternating Current versus Direct Current
    7. 20.6 Electric Hazards and the Human Body
    8. 20.7 Nerve Conduction–Electrocardiograms
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  22. 21 Circuits and DC Instruments
    1. Introduction to Circuits and DC Instruments
    2. 21.1 Resistors in Series and Parallel
    3. 21.2 Electromotive Force: Terminal Voltage
    4. 21.3 Kirchhoff’s Rules
    5. 21.4 DC Voltmeters and Ammeters
    6. 21.5 Null Measurements
    7. 21.6 DC Circuits Containing Resistors and Capacitors
    8. Glossary
    9. Section Summary
    10. Conceptual Questions
    11. Problems & Exercises
  23. 22 Magnetism
    1. Introduction to Magnetism
    2. 22.1 Magnets
    3. 22.2 Ferromagnets and Electromagnets
    4. 22.3 Magnetic Fields and Magnetic Field Lines
    5. 22.4 Magnetic Field Strength: Force on a Moving Charge in a Magnetic Field
    6. 22.5 Force on a Moving Charge in a Magnetic Field: Examples and Applications
    7. 22.6 The Hall Effect
    8. 22.7 Magnetic Force on a Current-Carrying Conductor
    9. 22.8 Torque on a Current Loop: Motors and Meters
    10. 22.9 Magnetic Fields Produced by Currents: Ampere’s Law
    11. 22.10 Magnetic Force between Two Parallel Conductors
    12. 22.11 More Applications of Magnetism
    13. Glossary
    14. Section Summary
    15. Conceptual Questions
    16. Problems & Exercises
  24. 23 Electromagnetic Induction, AC Circuits, and Electrical Technologies
    1. Introduction to Electromagnetic Induction, AC Circuits and Electrical Technologies
    2. 23.1 Induced Emf and Magnetic Flux
    3. 23.2 Faraday’s Law of Induction: Lenz’s Law
    4. 23.3 Motional Emf
    5. 23.4 Eddy Currents and Magnetic Damping
    6. 23.5 Electric Generators
    7. 23.6 Back Emf
    8. 23.7 Transformers
    9. 23.8 Electrical Safety: Systems and Devices
    10. 23.9 Inductance
    11. 23.10 RL Circuits
    12. 23.11 Reactance, Inductive and Capacitive
    13. 23.12 RLC Series AC Circuits
    14. Glossary
    15. Section Summary
    16. Conceptual Questions
    17. Problems & Exercises
  25. 24 Electromagnetic Waves
    1. Introduction to Electromagnetic Waves
    2. 24.1 Maxwell’s Equations: Electromagnetic Waves Predicted and Observed
    3. 24.2 Production of Electromagnetic Waves
    4. 24.3 The Electromagnetic Spectrum
    5. 24.4 Energy in Electromagnetic Waves
    6. Glossary
    7. Section Summary
    8. Conceptual Questions
    9. Problems & Exercises
  26. 25 Geometric Optics
    1. Introduction to Geometric Optics
    2. 25.1 The Ray Aspect of Light
    3. 25.2 The Law of Reflection
    4. 25.3 The Law of Refraction
    5. 25.4 Total Internal Reflection
    6. 25.5 Dispersion: The Rainbow and Prisms
    7. 25.6 Image Formation by Lenses
    8. 25.7 Image Formation by Mirrors
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  27. 26 Vision and Optical Instruments
    1. Introduction to Vision and Optical Instruments
    2. 26.1 Physics of the Eye
    3. 26.2 Vision Correction
    4. 26.3 Color and Color Vision
    5. 26.4 Microscopes
    6. 26.5 Telescopes
    7. 26.6 Aberrations
    8. Glossary
    9. Section Summary
    10. Conceptual Questions
    11. Problems & Exercises
  28. 27 Wave Optics
    1. Introduction to Wave Optics
    2. 27.1 The Wave Aspect of Light: Interference
    3. 27.2 Huygens's Principle: Diffraction
    4. 27.3 Young’s Double Slit Experiment
    5. 27.4 Multiple Slit Diffraction
    6. 27.5 Single Slit Diffraction
    7. 27.6 Limits of Resolution: The Rayleigh Criterion
    8. 27.7 Thin Film Interference
    9. 27.8 Polarization
    10. 27.9 *Extended Topic* Microscopy Enhanced by the Wave Characteristics of Light
    11. Glossary
    12. Section Summary
    13. Conceptual Questions
    14. Problems & Exercises
  29. 28 Special Relativity
    1. Introduction to Special Relativity
    2. 28.1 Einstein’s Postulates
    3. 28.2 Simultaneity And Time Dilation
    4. 28.3 Length Contraction
    5. 28.4 Relativistic Addition of Velocities
    6. 28.5 Relativistic Momentum
    7. 28.6 Relativistic Energy
    8. Glossary
    9. Section Summary
    10. Conceptual Questions
    11. Problems & Exercises
  30. 29 Introduction to Quantum Physics
    1. Introduction to Quantum Physics
    2. 29.1 Quantization of Energy
    3. 29.2 The Photoelectric Effect
    4. 29.3 Photon Energies and the Electromagnetic Spectrum
    5. 29.4 Photon Momentum
    6. 29.5 The Particle-Wave Duality
    7. 29.6 The Wave Nature of Matter
    8. 29.7 Probability: The Heisenberg Uncertainty Principle
    9. 29.8 The Particle-Wave Duality Reviewed
    10. Glossary
    11. Section Summary
    12. Conceptual Questions
    13. Problems & Exercises
  31. 30 Atomic Physics
    1. Introduction to Atomic Physics
    2. 30.1 Discovery of the Atom
    3. 30.2 Discovery of the Parts of the Atom: Electrons and Nuclei
    4. 30.3 Bohr’s Theory of the Hydrogen Atom
    5. 30.4 X Rays: Atomic Origins and Applications
    6. 30.5 Applications of Atomic Excitations and De-Excitations
    7. 30.6 The Wave Nature of Matter Causes Quantization
    8. 30.7 Patterns in Spectra Reveal More Quantization
    9. 30.8 Quantum Numbers and Rules
    10. 30.9 The Pauli Exclusion Principle
    11. Glossary
    12. Section Summary
    13. Conceptual Questions
    14. Problems & Exercises
  32. 31 Radioactivity and Nuclear Physics
    1. Introduction to Radioactivity and Nuclear Physics
    2. 31.1 Nuclear Radioactivity
    3. 31.2 Radiation Detection and Detectors
    4. 31.3 Substructure of the Nucleus
    5. 31.4 Nuclear Decay and Conservation Laws
    6. 31.5 Half-Life and Activity
    7. 31.6 Binding Energy
    8. 31.7 Tunneling
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  33. 32 Medical Applications of Nuclear Physics
    1. Introduction to Applications of Nuclear Physics
    2. 32.1 Medical Imaging and Diagnostics
    3. 32.2 Biological Effects of Ionizing Radiation
    4. 32.3 Therapeutic Uses of Ionizing Radiation
    5. 32.4 Food Irradiation
    6. 32.5 Fusion
    7. 32.6 Fission
    8. 32.7 Nuclear Weapons
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  34. 33 Particle Physics
    1. Introduction to Particle Physics
    2. 33.1 The Yukawa Particle and the Heisenberg Uncertainty Principle Revisited
    3. 33.2 The Four Basic Forces
    4. 33.3 Accelerators Create Matter from Energy
    5. 33.4 Particles, Patterns, and Conservation Laws
    6. 33.5 Quarks: Is That All There Is?
    7. 33.6 GUTs: The Unification of Forces
    8. Glossary
    9. Section Summary
    10. Conceptual Questions
    11. Problems & Exercises
  35. 34 Frontiers of Physics
    1. Introduction to Frontiers of Physics
    2. 34.1 Cosmology and Particle Physics
    3. 34.2 General Relativity and Quantum Gravity
    4. 34.3 Superstrings
    5. 34.4 Dark Matter and Closure
    6. 34.5 Complexity and Chaos
    7. 34.6 High-temperature Superconductors
    8. 34.7 Some Questions We Know to Ask
    9. Glossary
    10. Section Summary
    11. Conceptual Questions
    12. Problems & Exercises
  36. A | Atomic Masses
  37. B | Selected Radioactive Isotopes
  38. C | Useful Information
  39. D | Glossary of Key Symbols and Notation
  40. Index

21.1 Resistors in Series and Parallel

Note: Data taken from figures can be assumed to be accurate to three significant digits.

1.

(a) What is the resistance of ten 275-Ω275-Ω size 12{"275"- %OMEGA } {} resistors connected in series? (b) In parallel?

2.

(a) What is the resistance of a 1.00×1021.00×102, a 2.50-kΩ2.50-kΩ, and a 4.00-kΩ4.00-kΩ size 12{4 "." "00""-k" %OMEGA } {} resistor connected in series? (b) In parallel?

3.

What are the largest and smallest resistances you can obtain by connecting a 36.0-Ω36.0-Ω, a 50.0-Ω50.0-Ω size 12{"50" "." 0- %OMEGA } {}, and a 700-Ω700-Ω size 12{"700"- %OMEGA } {} resistor together?

4.

An 1800-W toaster, a 1400-W electric frying pan, and a 75-W lamp are plugged into the same outlet in a 15-A, 120-V circuit. (The three devices are in parallel when plugged into the same socket.). (a) What current is drawn by each device? (b) Will this combination blow the 15-A fuse?

5.

Your car’s 30.0-W headlight and 2.40-kW starter are ordinarily connected in parallel in a 12.0-V system. What power would one headlight and the starter consume if connected in series to a 12.0-V battery? (Neglect any other resistance in the circuit and any change in resistance in the two devices.)

6.

(a) Given a 48.0-V battery and 24.0-Ω24.0-Ω size 12{"24" "." 0- %OMEGA } {} and 96.0-Ω96.0-Ω size 12{"96" "." 0- %OMEGA } {} resistors, find the current and power for each when connected in series. (b) Repeat when the resistances are in parallel.

7.

Referring to the example combining series and parallel circuits and Figure 21.6, calculate I3I3 size 12{I rSub { size 8{3} } } {} in the following two different ways: (a) from the known values of II size 12{I} {} and I2I2 size 12{I rSub { size 8{2} } } {}; (b) using Ohm’s law for R3R3 size 12{R rSub { size 8{3} } } {}. In both parts explicitly show how you follow the steps in the Problem-Solving Strategies for Series and Parallel Resistors.

8.

Referring to Figure 21.6: (a) Calculate P3P3 size 12{P rSub { size 8{3} } } {} and note how it compares with P3P3 size 12{P rSub { size 8{3} } } {} found in the first two example problems in this module. (b) Find the total power supplied by the source and compare it with the sum of the powers dissipated by the resistors.

9.

Refer to Figure 21.7 and the discussion of lights dimming when a heavy appliance comes on. (a) Given the voltage source is 120 V, the wire resistance is 0.400Ω0.400Ω size 12{0 "." "800" %OMEGA } {}, and the bulb is nominally 75.0 W, what power will the bulb dissipate if a total of 15.0 A passes through the wires when the motor comes on? Assume negligible change in bulb resistance. (b) What power is consumed by the motor?

10.

A 240-kV power transmission line carrying 5.00×102A5.00×102A is hung from grounded metal towers by ceramic insulators, each having a 1.00×1091.00×109 size 12{1 "." "00"´"10" rSup { size 8{9} } - %OMEGA } {} resistance. Figure 21.51. (a) What is the resistance to ground of 100 of these insulators? (b) Calculate the power dissipated by 100 of them. (c) What fraction of the power carried by the line is this? Explicitly show how you follow the steps in the Problem-Solving Strategies for Series and Parallel Resistors.

The diagram shows a grounded metal transmission tower. Two ground conductors on top of the tower point out like antennas. Hanging from the tower are a set of three bundled conductors, one on either end and one in the middle.
Figure 21.51 High-voltage (240-kV) transmission line carrying 5.00×102A5.00×102A is hung from a grounded metal transmission tower. The row of ceramic insulators provide 1.00×109Ω1.00×109Ω size 12{1 "." 0 times "10" rSup { size 8{9} } %OMEGA } {} of resistance each.
11.

Show that if two resistors R1R1 size 12{R rSub { size 8{1} } } {} and R2R2 size 12{R rSub { size 8{2} } } {} are combined and one is much greater than the other (R1>>R2R1>>R2 size 12{R rSub { size 8{1} } ">>"R rSub { size 8{2} } } {}): (a) Their series resistance is very nearly equal to the greater resistance R1R1 size 12{R rSub { size 8{1} } } {}. (b) Their parallel resistance is very nearly equal to smaller resistance R2R2 size 12{R rSub { size 8{2} } } {}.

12.

Unreasonable Results

Two resistors, one having a resistance of 145 Ω145 Ω size 12{1"45 " %OMEGA } {}, are connected in parallel to produce a total resistance of 150Ω150Ω size 12{150 %OMEGA } {}. (a) What is the value of the second resistance? (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?

13.

Unreasonable Results

Two resistors, one having a resistance of 900 kΩ900 kΩ size 12{9"00 k" %OMEGA } {}, are connected in series to produce a total resistance of 0.500 MΩ0.500 MΩ size 12{0 "." "500 M" %OMEGA } {}. (a) What is the value of the second resistance? (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?

21.2 Electromotive Force: Terminal Voltage

14.

Standard automobile batteries have six lead-acid cells in series, creating a total emf of 12.0 V. What is the emf of an individual lead-acid cell?

15.

Carbon-zinc dry cells (sometimes referred to as non-alkaline cells) have an emf of 1.54 V, and they are produced as single cells or in various combinations to form other voltages. (a) How many 1.54-V cells are needed to make the common 9-V battery used in many small electronic devices? (b) What is the actual emf of the approximately 9-V battery? (c) Discuss how internal resistance in the series connection of cells will affect the terminal voltage of this approximately 9-V battery.

16.

What is the output voltage of a 3.0000-V lithium cell in a digital wristwatch that draws 0.300 mA, if the cell’s internal resistance is 2.00Ω2.00Ω size 12{2 "." "00" %OMEGA } {}?

17.

(a) What is the terminal voltage of a large 1.54-V carbon-zinc dry cell used in a physics lab to supply 2.00 A to a circuit, if the cell’s internal resistance is 0.100 Ω0.100 Ω size 12{0 "." "100" %OMEGA } {}? (b) How much electrical power does the cell produce? (c) What power goes to its load?

18.

What is the internal resistance of an automobile battery that has an emf of 12.0 V and a terminal voltage of 15.0 V while a current of 8.00 A is charging it?

19.

(a) Find the terminal voltage of a 12.0-V motorcycle battery having a 0.600-Ω0.600-Ω size 12{0 "." "600"- %OMEGA } {} internal resistance, if it is being charged by a current of 10.0 A. (b) What is the output voltage of the battery charger?

20.

A car battery with a 12-V emf and an internal resistance of 0.050Ω0.050Ω size 12{0 "." "050" %OMEGA } {} is being charged with a current of 60 A. Note that in this process the battery is being charged. (a) What is the potential difference across its terminals? (b) At what rate is thermal energy being dissipated in the battery? (c) At what rate is electric energy being converted to chemical energy? (d) What are the answers to (a) and (b) when the battery is used to supply 60 A to the starter motor?

21.

The hot resistance of a flashlight bulb is 2.30Ω2.30Ω size 12{2 "." "30" %OMEGA } {}, and it is run by a 1.58-V alkaline cell having a 0.100-Ω0.100-Ω size 12{0 "." "100"- %OMEGA } {} internal resistance. (a) What current flows? (b) Calculate the power supplied to the bulb using I2RbulbI2Rbulb size 12{I rSup { size 8{2} } R rSub { size 8{"bulb"} } } {}. (c) Is this power the same as calculated using V2RbulbV2Rbulb size 12{ { {V rSup { size 8{2} } } over {R rSub { size 8{"bulb"} } } } } {}?

22.

The label on a portable radio recommends the use of rechargeable nickel-cadmium cells (nicads), although they have a 1.25-V emf while alkaline cells have a 1.58-V emf. The radio has a 3.20-Ω3.20-Ω size 12{3 "." "20"- %OMEGA } {} resistance. (a) Draw a circuit diagram of the radio and its batteries. Now, calculate the power delivered to the radio. (b) When using Nicad cells each having an internal resistance of 0.0400 Ω0.0400 Ω size 12{0 "." "0400" %OMEGA } {}. (c) When using alkaline cells each having an internal resistance of 0.200 Ω0.200 Ω size 12{0 "." "200" %OMEGA } {}. (d) Does this difference seem significant, considering that the radio’s effective resistance is lowered when its volume is turned up?

23.

An automobile starter motor has an equivalent resistance of 0.0500Ω0.0500Ω size 12{0 "." "0500" %OMEGA } {} and is supplied by a 12.0-V battery with a 0.0100-Ω0.0100-Ω size 12{0 "." "0100"- %OMEGA } {} internal resistance. (a) What is the current to the motor? (b) What voltage is applied to it? (c) What power is supplied to the motor? (d) Repeat these calculations for when the battery connections are corroded and add 0.0900Ω0.0900Ω size 12{0 "." "0900" %OMEGA } {} to the circuit. (Significant problems are caused by even small amounts of unwanted resistance in low-voltage, high-current applications.)

24.

A child’s electronic toy is supplied by three 1.58-V alkaline cells having internal resistances of 0.0200Ω0.0200Ω size 12{0 "." "0200" %OMEGA } {} in series with a 1.53-V carbon-zinc dry cell having a 0.100-Ω0.100-Ω size 12{0 "." "100"- %OMEGA } {} internal resistance. The load resistance is 10.0Ω10.0Ω size 12{"10" "." 0 %OMEGA } {}. (a) Draw a circuit diagram of the toy and its batteries. (b) What current flows? (c) How much power is supplied to the load? (d) What is the internal resistance of the dry cell if it goes bad, resulting in only 0.500 W being supplied to the load?

25.

(a) What is the internal resistance of a voltage source if its terminal voltage drops by 2.00 V when the current supplied increases by 5.00 A? (b) Can the emf of the voltage source be found with the information supplied?

26.

A person with body resistance between his hands of 10.0 kΩ10.0 kΩ size 12{"10" "." 0" k" %OMEGA } {} accidentally grasps the terminals of a 20.0-kV power supply. (Do NOT do this!) (a) Draw a circuit diagram to represent the situation. (b) If the internal resistance of the power supply is 2000Ω2000Ω size 12{"2000" %OMEGA } {}, what is the current through his body? (c) What is the power dissipated in his body? (d) If the power supply is to be made safe by increasing its internal resistance, what should the internal resistance be for the maximum current in this situation to be 1.00 mA or less? (e) Will this modification compromise the effectiveness of the power supply for driving low-resistance devices? Explain your reasoning.

27.

Electric fish generate current with biological cells called electroplaques, which are physiological emf devices. The electroplaques in the South American eel are arranged in 140 rows, each row stretching horizontally along the body and each containing 5000 electroplaques. Each electroplaque has an emf of 0.15 V and internal resistance of 0.25Ω0.25Ω size 12{0 "." "25" %OMEGA } {}. If the water surrounding the fish has resistance of 800Ω800Ω size 12{"800" %OMEGA } {}, how much current can the eel produce in water from near its head to near its tail?

28.

Integrated Concepts

A 12.0-V emf automobile battery has a terminal voltage of 16.0 V when being charged by a current of 10.0 A. (a) What is the battery’s internal resistance? (b) What power is dissipated inside the battery? (c) At what rate (in ºC/minºC/min size 12{°"C/min"} {}) will its temperature increase if its mass is 20.0 kg and it has a specific heat of 0.300 kcal/kgºC0.300 kcal/kgºC size 12{0 "." "300"" kcal/kg" cdot °C} {}, assuming no heat escapes?

29.

Unreasonable Results

A 1.58-V alkaline cell with a 0.200-Ω0.200-Ω size 12{0 "." "200"- %OMEGA } {} internal resistance is supplying 8.50 A to a load. (a) What is its terminal voltage? (b) What is the value of the load resistance? (c) What is unreasonable about these results? (d) Which assumptions are unreasonable or inconsistent?

30.

Unreasonable Results

(a) What is the internal resistance of a 1.54-V dry cell that supplies 1.00 W of power to a 15.0-Ω15.0-Ω size 12{"15" "." 0- %OMEGA } {} bulb? (b) What is unreasonable about this result? (c) Which assumptions are unreasonable or inconsistent?

21.3 Kirchhoff’s Rules

31.

Apply the loop rule to loop abcdefgha in Figure 21.25.

32.

Apply the loop rule to loop aedcba in Figure 21.25.

33.

Verify the second equation in Example 21.5 by substituting the values found for the currents I1I1 size 12{I rSub { size 8{1} } } {} and I2I2 size 12{I rSub { size 8{2} } } {}.

34.

Verify the third equation in Example 21.5 by substituting the values found for the currents I1I1 size 12{I rSub { size 8{1} } } {} and I3I3 size 12{I rSub { size 8{3} } } {}.

35.

Apply the junction rule at point a in Figure 21.52.

The diagram shows a complex circuit with four voltage sources E sub one, E sub two, E sub three, E sub four and several resistive loads, wired in two loops and many junctions. Several points on the diagram are marked with letters a through j. The current in each branch is labeled separately.
Figure 21.52
36.

Apply the loop rule to loop abcdefghija in Figure 21.52.

37.

Apply the loop rule to loop akledcba in Figure 21.52.

38.

Find the currents flowing in the circuit in Figure 21.52. Explicitly show how you follow the steps in the Problem-Solving Strategies for Series and Parallel Resistors.

39.

Solve Example 21.5, but use loop abcdefgha instead of loop akledcba. Explicitly show how you follow the steps in the Problem-Solving Strategies for Series and Parallel Resistors.

40.

Find the currents flowing in the circuit in Figure 21.47.

41.

Unreasonable Results

Consider the circuit in Figure 21.53, and suppose that the emfs are unknown and the currents are given to be I1=5.00 AI1=5.00 A, I2=3.0 AI2=3.0 A size 12{I rSub { size 8{2} } =3 "." 0" A"} {}, and I3=–2.00 AI3=–2.00 A size 12{I rSub { size 8{3} } "=-"2 "." "00"" A"} {}. (a) Could you find the emfs? (b) What is wrong with the assumptions?

The diagram shows a complex circuit with two voltage sources E sub one and E sub two, and three resistive loads, wired in two loops and two junctions. Several points on the diagram are marked with letters a through h. The current in each branch is labeled separately.
Figure 21.53

21.4 DC Voltmeters and Ammeters

42.

What is the sensitivity of the galvanometer (that is, what current gives a full-scale deflection) inside a voltmeter that has a 1.00-MΩ1.00-MΩ size 12{1 "." "00""-M" %OMEGA } {} resistance on its 30.0-V scale?

43.

What is the sensitivity of the galvanometer (that is, what current gives a full-scale deflection) inside a voltmeter that has a 25.0-kΩ25.0-kΩ size 12{"25" "." 0"-k" %OMEGA } {} resistance on its 100-V scale?

44.

Find the resistance that must be placed in series with a 25.0-Ω25.0-Ω size 12{"25" "." 0- %OMEGA } {} galvanometer having a 50.0-μA50.0-μA size 12{"50" "." 0-μA} {} sensitivity (the same as the one discussed in the text) to allow it to be used as a voltmeter with a 0.100-V full-scale reading.

45.

Find the resistance that must be placed in series with a 25.0-Ω25.0-Ω size 12{"25" "." 0- %OMEGA } {} galvanometer having a 50.0-μA50.0-μA size 12{"50" "." 0-μA} {} sensitivity (the same as the one discussed in the text) to allow it to be used as a voltmeter with a 3000-V full-scale reading. Include a circuit diagram with your solution.

46.

Find the resistance that must be placed in parallel with a 25.0-Ω25.0-Ω size 12{"25" "." 0- %OMEGA } {} galvanometer having a 50.0-μA50.0-μA size 12{"50" "." 0-μA} {} sensitivity (the same as the one discussed in the text) to allow it to be used as an ammeter with a 10.0-A full-scale reading. Include a circuit diagram with your solution.

47.

Find the resistance that must be placed in parallel with a 25.0-Ω25.0-Ω size 12{"25" "." 0- %OMEGA } {} galvanometer having a 50.0-μA50.0-μA size 12{"50" "." 0-μA} {} sensitivity (the same as the one discussed in the text) to allow it to be used as an ammeter with a 300-mA full-scale reading.

48.

Find the resistance that must be placed in series with a 10.0-Ω10.0-Ω size 12{"10" "." 0- %OMEGA } {} galvanometer having a 100-μA100-μA size 12{"100"-μA} {} sensitivity to allow it to be used as a voltmeter with: (a) a 300-V full-scale reading, and (b) a 0.300-V full-scale reading.

49.

Find the resistance that must be placed in parallel with a 10.0-Ω10.0-Ω size 12{"10" "." 0- %OMEGA } {} galvanometer having a 100-μA100-μA size 12{"100"-μA} {} sensitivity to allow it to be used as an ammeter with: (a) a 20.0-A full-scale reading, and (b) a 100-mA full-scale reading.

50.

Suppose you measure the terminal voltage of a 1.585-V alkaline cell having an internal resistance of 0.100Ω0.100Ω size 12{0 "." "100" %OMEGA } {} by placing a 1.00-kΩ1.00-kΩ size 12{1 "." "00""-k" %OMEGA } {} voltmeter across its terminals. (See Figure 21.54.) (a) What current flows? (b) Find the terminal voltage. (c) To see how close the measured terminal voltage is to the emf, calculate their ratio.

The figure shows a circuit diagram that includes a battery with an internal resistance r and a voltmeter connected across its terminals. The current I is shown by an arrow pointing in a clockwise direction.
Figure 21.54
51.

Suppose you measure the terminal voltage of a 3.200-V lithium cell having an internal resistance of 5.00Ω5.00Ω size 12{5 "." "00" %OMEGA } {} by placing a 1.00-kΩ1.00-kΩ size 12{1 "." "00""-k" %OMEGA } {} voltmeter across its terminals. (a) What current flows? (b) Find the terminal voltage. (c) To see how close the measured terminal voltage is to the emf, calculate their ratio.

52.

A certain ammeter has a resistance of 5.00×105Ω5.00×105Ω size 12{5 "." "00"´"10" rSup { size 8{-5} } %OMEGA } {} on its 3.00-A scale and contains a 10.0-Ω10.0-Ω size 12{"10" "." 0- %OMEGA } {} galvanometer. What is the sensitivity of the galvanometer?

53.

A 1.00-MΩ1.00-MΩ size 12{1 "." "00""-M" %OMEGA } {} voltmeter is placed in parallel with a 75.0-kΩ75.0-kΩ size 12{"75" "." 0"-k" %OMEGA } {} resistor in a circuit. (a) Draw a circuit diagram of the connection. (b) What is the resistance of the combination? (c) If the voltage across the combination is kept the same as it was across the 75.0-kΩ75.0-kΩ size 12{"75" "." 0"-k" %OMEGA } {} resistor alone, what is the percent increase in current? (d) If the current through the combination is kept the same as it was through the 75.0-kΩ75.0-kΩ size 12{"75" "." 0"-k" %OMEGA } {} resistor alone, what is the percentage decrease in voltage? (e) Are the changes found in parts (c) and (d) significant? Discuss.

54.

A 0.0200-Ω0.0200-Ω ammeter is placed in series with a 10.00-Ω10.00-Ω size 12{"10" "." "00"- %OMEGA } {} resistor in a circuit. (a) Draw a circuit diagram of the connection. (b) Calculate the resistance of the combination. (c) If the voltage is kept the same across the combination as it was through the 10.00-Ω10.00-Ω size 12{"10" "." "00"- %OMEGA } {} resistor alone, what is the percent decrease in current? (d) If the current is kept the same through the combination as it was through the 10.00-Ω10.00-Ω size 12{"10" "." "00"- %OMEGA } {} resistor alone, what is the percent increase in voltage? (e) Are the changes found in parts (c) and (d) significant? Discuss.

55.

Unreasonable Results

Suppose you have a 40.0-Ω40.0-Ω size 12{"40" "." 0- %OMEGA } {} galvanometer with a 25.0-μA25.0-μA size 12{"25" "." 0-mA} {} sensitivity. (a) What resistance would you put in series with it to allow it to be used as a voltmeter that has a full-scale deflection for 0.500 mV? (b) What is unreasonable about this result? (c) Which assumptions are responsible?

56.

Unreasonable Results

(a) What resistance would you put in parallel with a 40.0-Ω40.0-Ω size 12{"40" "." 0- %OMEGA } {} galvanometer having a 25.0-μA25.0-μA sensitivity to allow it to be used as an ammeter that has a full-scale deflection for 10.0-μA 10.0-μA size 12{"10" "." 0 μA} {}? (b) What is unreasonable about this result? (c) Which assumptions are responsible?

21.5 Null Measurements

57.

What is the emfxemfx size 12{"emf" rSub { size 8{x} } } {} of a cell being measured in a potentiometer, if the standard cell’s emf is 12.0 V and the potentiometer balances for Rx=5.000ΩRx=5.000Ω size 12{R rSub { size 8{x} } =5 "." "000" %OMEGA } {} and Rs=2.500ΩRs=2.500Ω size 12{R rSub { size 8{s} } =2 "." "500" %OMEGA } {}?

58.

Calculate the emfxemfx size 12{"emf" rSub { size 8{x} } } {} of a dry cell for which a potentiometer is balanced when Rx=1.200ΩRx=1.200Ω size 12{R rSub { size 8{x} } =1 "." "200" %OMEGA } {}, while an alkaline standard cell with an emf of 1.600 V requires Rs=1.247ΩRs=1.247Ω size 12{R rSub { size 8{s} } =1 "." "247" %OMEGA } {} to balance the potentiometer.

59.

When an unknown resistance RxRx size 12{R rSub { size 8{x} } } {} is placed in a Wheatstone bridge, it is possible to balance the bridge by adjusting R3R3 size 12{R rSub { size 8{3} } } {} to be 2500Ω2500Ω size 12{"2500" %OMEGA } {}. What is RxRx size 12{R rSub { size 8{x} } } {} if R2R1=0.625R2R1=0.625 size 12{ { {R rSub { size 8{2} } } over {R rSub { size 8{1} } } } =0 "." "625"} {}?

60.

To what value must you adjust R3R3 size 12{R rSub { size 8{3} } } {} to balance a Wheatstone bridge, if the unknown resistance RxRx size 12{R rSub { size 8{x} } } {} is 100Ω100Ω size 12{"100" %OMEGA } {}, R1R1 size 12{R rSub { size 8{1} } } {} is 50.0Ω50.0Ω size 12{"50" "." 0 %OMEGA } {}, and R2R2 size 12{R rSub { size 8{2} } } {} is 175Ω175Ω size 12{"175" %OMEGA } {}?

61.

(a) What is the unknown emfxemfx size 12{"emf" rSub { size 8{x} } } {} in a potentiometer that balances when RxRx size 12{R rSub { size 8{x} } } {} is 10.0Ω10.0Ω size 12{"10" "." 0 %OMEGA } {}, and balances when RsRs size 12{R rSub { size 8{s} } } {} is 15.0Ω15.0Ω size 12{"15" "." 0 %OMEGA } {} for a standard 3.000-V emf? (b) The same emfxemfx size 12{"emf" rSub { size 8{x} } } {} is placed in the same potentiometer, which now balances when RsRs size 12{R rSub { size 8{s} } } {} is 15.0Ω15.0Ω size 12{"15" "." 0 %OMEGA } {} for a standard emf of 3.100 V. At what resistance RxRx size 12{R rSub { size 8{x} } } {} will the potentiometer balance?

62.

Suppose you want to measure resistances in the range from 10.0Ω10.0Ω size 12{"10" "." 0 %OMEGA } {} to 10.0 kΩ10.0 kΩ size 12{"10" "." 0" k" %OMEGA } {} using a Wheatstone bridge that has R2R1=2.000R2R1=2.000 size 12{ { {R rSub { size 8{2} } } over {R rSub { size 8{1} } } } =2 "." "000"} {}. Over what range should R3R3 size 12{R rSub { size 8{3} } } {} be adjustable?

21.6 DC Circuits Containing Resistors and Capacitors

63.

The timing device in an automobile’s intermittent wiper system is based on an RCRC size 12{ ital "RC"} {} time constant and utilizes a 0.500-μF0.500-μF size 12{0 "." "500-"μF} {} capacitor and a variable resistor. Over what range must RR size 12{R} {} be made to vary to achieve time constants from 2.00 to 15.0 s?

64.

A heart pacemaker fires 72 times a minute, each time a 25.0-nF capacitor is charged (by a battery in series with a resistor) to 0.632 of its full voltage. What is the value of the resistance?

65.

The duration of a photographic flash is related to an RCRC size 12{ ital "RC"} {} time constant, which is 0.100 μs0.100 μs size 12{0 "." "100" μs} {} for a certain camera. (a) If the resistance of the flash lamp is 0.0400Ω0.0400Ω size 12{0 "." "0400" %OMEGA } {} during discharge, what is the size of the capacitor supplying its energy? (b) What is the time constant for charging the capacitor, if the charging resistance is 800800 size 12{"800"" k" %OMEGA } {}?

66.

A 2.00- and a 7.50-μF7.50-μF size 12{7 "." "50"-mF} {} capacitor can be connected in series or parallel, as can a 25.0- and a 100-kΩ100-kΩ size 12{"100""-k" %OMEGA } {} resistor. Calculate the four RCRC size 12{ ital "RC"} {} time constants possible from connecting the resulting capacitance and resistance in series.

67.

After two time constants, what percentage of the final voltage, emf, is on an initially uncharged capacitor CC size 12{C} {}, charged through a resistance RR size 12{R} {}?

68.

A 500-Ω500-Ω size 12{"500"- %OMEGA } {} resistor, an uncharged 1.50-μF1.50-μF size 12{1 "." "50"-mF} {} capacitor, and a 6.16-V emf are connected in series. (a) What is the initial current? (b) What is the RCRC size 12{ ital "RC"} {} time constant? (c) What is the current after one time constant? (d) What is the voltage on the capacitor after one time constant?

69.

A heart defibrillator being used on a patient has an RCRC size 12{ ital "RC"} {} time constant of 10.0 ms due to the resistance of the patient and the capacitance of the defibrillator. (a) If the defibrillator has an 8.00-μF8.00-μF size 12{8 "." "00"-mF} {} capacitance, what is the resistance of the path through the patient? (You may neglect the capacitance of the patient and the resistance of the defibrillator.) (b) If the initial voltage is 12.0 kV, how long does it take to decline to 6.00×102V6.00×102V?

70.

An ECG monitor must have an RCRC size 12{ ital "RC"} {} time constant less than 1.00×102μs1.00×102μs size 12{"100" ms} {} to be able to measure variations in voltage over small time intervals. (a) If the resistance of the circuit (due mostly to that of the patient’s chest) is 1.00 kΩ1.00 kΩ size 12{1 "." 00" k" %OMEGA } {}, what is the maximum capacitance of the circuit? (b) Would it be difficult in practice to limit the capacitance to less than the value found in (a)?

71.

Figure 21.55 shows how a bleeder resistor is used to discharge a capacitor after an electronic device is shut off, allowing a person to work on the electronics with less risk of shock. (a) What is the time constant? (b) How long will it take to reduce the voltage on the capacitor to 0.250% (5% of 5%) of its full value once discharge begins? (c) If the capacitor is charged to a voltage V0V0 size 12{V rSub { size 8{0} } } {} through a 100-Ω100-Ω size 12{"100"- %OMEGA } {} resistance, calculate the time it takes to rise to 0.865V00.865V0 size 12{0 "." "865"`V rSub { size 8{0} } } {} (This is about two time constants.)

A parallel circuit with a switch, an embedded electronic circuit, a capacitor, and a resistor is shown. The embedded circuit, capacitor, and resistor are connected in parallel with each other: the electronic circuit on the left, the capacitor in the middle, and the resistor on the right. The capacitor has a capacitance of eighty micro farads. The resistor has a resistance of two hundred fifty kilohms. The switch is on the top, between the electronic circuit and the capacitor leg.
Figure 21.55
72.

Using the exact exponential treatment, find how much time is required to discharge a 250-μF250-μF size 12{"250"-mF} {} capacitor through a 500-Ω500-Ω size 12{"500"- %OMEGA } {} resistor down to 1.00% of its original voltage.

73.

Using the exact exponential treatment, find how much time is required to charge an initially uncharged 100-pF capacitor through a 75.0-MΩ75.0-MΩ size 12{"75" "." 0"-M" %OMEGA } {} resistor to 90.0% of its final voltage.

74.

Integrated Concepts

If you wish to take a picture of a bullet traveling at 500 m/s, then a very brief flash of light produced by an RCRC size 12{ ital "RC"} {} discharge through a flash tube can limit blurring. Assuming 1.00 mm of motion during one RCRC size 12{ ital "RC"} {} constant is acceptable, and given that the flash is driven by a 600-μF600-μF size 12{"600"-mF} {} capacitor, what is the resistance in the flash tube?

75.

Integrated Concepts

A flashing lamp in a Christmas earring is based on an RCRC size 12{ ital "RC"} {} discharge of a capacitor through its resistance. The effective duration of the flash is 0.250 s, during which it produces an average 0.500 W from an average 3.00 V. (a) What energy does it dissipate? (b) How much charge moves through the lamp? (c) Find the capacitance. (d) What is the resistance of the lamp?

76.

Integrated Concepts

A 160-μF160-μF size 12{"160"-mF} {} capacitor charged to 450 V is discharged through a 31.2-kΩ31.2-kΩ size 12{31 "." "2-k" %OMEGA } {} resistor. (a) Find the time constant. (b) Calculate the temperature increase of the resistor, given that its mass is 2.50 g and its specific heat is 1.67kJkgºC1.67kJkgºC size 12{1 "." "67" { {"kJ"} over {"kg" cdot "deg"C} } } {}, noting that most of the thermal energy is retained in the short time of the discharge. (c) Calculate the new resistance, assuming it is pure carbon. (d) Does this change in resistance seem significant?

77.

Unreasonable Results

(a) Calculate the capacitance needed to get an RCRC size 12{ ital "RC"} {} time constant of 1.00×103s1.00×103s with a 0.100-Ω0.100-Ω size 12{0 "." "100"- %OMEGA } {} resistor. (b) What is unreasonable about this result? (c) Which assumptions are responsible?

78.

Construct Your Own Problem

Consider a camera’s flash unit. Construct a problem in which you calculate the size of the capacitor that stores energy for the flash lamp. Among the things to be considered are the voltage applied to the capacitor, the energy needed in the flash and the associated charge needed on the capacitor, the resistance of the flash lamp during discharge, and the desired RCRC size 12{ ital "RC"} {} time constant.

79.

Construct Your Own Problem

Consider a rechargeable lithium cell that is to be used to power a camcorder. Construct a problem in which you calculate the internal resistance of the cell during normal operation. Also, calculate the minimum voltage output of a battery charger to be used to recharge your lithium cell. Among the things to be considered are the emf and useful terminal voltage of a lithium cell and the current it should be able to supply to a camcorder.

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