Physics

# Problems

PhysicsProblems

## 18.1Electrical Charges, Conservation of Charge, and Transfer of Charge

25.

A dust particle acquires a charge of −13 nC. How many excess electrons does it carry?

1. 20.8 × 10−28 electrons
2. 20.8 × −19 electrons
3. 8.1 × 1010 electrons
4. 8.1 × 1019 electrons
26.

Two identical conducting spheres are charged with a net charge of +5.0 q on the first sphere and a net charge of −8.0 q on the second sphere. The spheres are brought together, allowed to touch, and then separated. What is the net charge on each sphere now?

1. −3.0q
2. −1.5q
3. +1.5q
4. +3.0q

## 18.2Coulomb's law

27.

Two plastic spheres with uniform charge repel each other with a force of 10 N. If you remove the charge from one sphere, what will be the force between the spheres?

1. -5.8 × 10-10 C
2. The force will be 15 N.
3. The force will be 10 N.
4. The force will be 5 N.
5. The force will be zero.
28.

Three charges are on a line. The left charge is q1 = 2.0 nC . The middle charge is q2 = 5.0 nC . The right charge is q3 = − 3.0 nC . The left and right charges are 2.0 cm from the middle charge. What is the force on the middle charge?

1. −5.6 × 10−4 N to the left
2. −1.12 × 10−4 N to the left
3. +1.12 × 10−4 N to the right
4. 5.6 × 10−4 N to the right

## 18.3Electric Field

29.

An electric field (15 N/C) applies a force (− 3 × 10–6 N) on a particle. What is the charge on the particle?

1. −2.0 × 10–7 C
2. 2.0 × 10–7 C
3. 2.0 × 10–8 C
4. 2.0 × 10–9 C
30.

Two uniform electric fields are superimposed. The first electric field is . The second electric field is . With respect to the positive x axis, at which angle will a positive test charge accelerate in this combined field?

1. 27°
2. 54°
3. 90°
4. 108°

## 18.4Electric Potential

31.

You move a charge q from ri = 20 cm to rf = 40 cm from a fixed charge Q = 10 nC. What is the difference in potential for these two positions?

1. −2.2 × 102 V
2. −1.7 × 103 V
3. −2.2 × 104 V
4. −1.7 × 102 V
32.

How much work is required from an outside agent to move an electron from xi = 0 to xf = 20 cm in an electric field $(50 N/C) x ^ (50 N/C) x ^$ ?

1. 1.6 × 10−15 J
2. 1.6 × 10−16 J
3. 1.6 × 10−20 J
4. 1.6 × 10−18 J

## 18.5Capacitors and Dielectrics

33.

A 4.12 µF parallel-plate capacitor has a plate area of 2,000 cm2 and a plate separation of 10 µm . What dielectric is between the plates?

1. 1, the dielectric is strontium titanate
2. 466, the dielectric is strontium
3. 699, the dielectric is strontium nitrate
4. 1,000, the dielectric is strontium chloride
34 .
What is the capacitance of a metal sphere of radius $R$?
1. $C = \frac{R}{k}$
2. $C = \frac{k}{R}$
3. $C = \frac{V}{Q}$
4. $C = QV$
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