College Physics for AP® Courses

# Glossary

College Physics for AP® CoursesGlossary

back emf
the emf generated by a running motor, because it consists of a coil turning in a magnetic field; it opposes the voltage powering the motor
capacitive reactance
the opposition of a capacitor to a change in current; calculated by $XC=12πfCXC=12πfC size 12{X rSub { size 8{C} } = { {1} over {2π ital "fC"} } } {}$
characteristic time constant
denoted by $ττ size 12{τ} {}$, of a particular series RL circuit is calculated by $τ=LRτ=LR size 12{τ= { {L} over {R} } } {}$, where $LL size 12{L} {}$ is the inductance and $RR$ is the resistance
eddy current
a current loop in a conductor caused by motional emf
electric generator
a device for converting mechanical work into electric energy; it induces an emf by rotating a coil in a magnetic field
electromagnetic induction
the process of inducing an emf (voltage) with a change in magnetic flux
emf induced in a generator coil
$emf=NABωsinωtemf=NABωsinωt size 12{"emf"= ital "NAB"ω"sin"ωt} {}$, where $A A$ is the area of an $N N$-turn coil rotated at a constant angular velocity $ω ω$ in a uniform magnetic field $B B$, over a period of time $t t$
energy stored in an inductor
self-explanatory; calculated by $Eind=12LI2Eind=12LI2 size 12{E rSub { size 8{"ind"} } = { {1} over {2} } ital "LI" rSup { size 8{2} } } {}$
the means of calculating the emf in a coil due to changing magnetic flux, given by $emf = − N ΔΦ Δt emf = − N ΔΦ Δt size 12{"emf"= - N { {ΔΦ} over {Δt} } } {}$
henry
the unit of inductance; $1H=1Ω⋅s1H=1Ω⋅s size 12{1H=1 %OMEGA cdot s} {}$
impedance
the AC analogue to resistance in a DC circuit; it is the combined effect of resistance, inductive reactance, and capacitive reactance in the form $Z=R2+(XL−XC)2Z=R2+(XL−XC)2 size 12{Z= sqrt {R rSup { size 8{2} } + $$X rSub { size 8{L} } - X rSub { size 8{C} }$$ rSup { size 8{2} } } } {}$
inductance
a property of a device describing how efficient it is at inducing emf in another device
induction
(magnetic induction) the creation of emfs and hence currents by magnetic fields
inductive reactance
the opposition of an inductor to a change in current; calculated by $XL=2πfLXL=2πfL size 12{X rSub { size 8{L} } =2π ital "fL"} {}$
inductor
a device that exhibits significant self-inductance
Lenz’s law
the minus sign in Faraday’s law, signifying that the emf induced in a coil opposes the change in magnetic flux
magnetic damping
the drag produced by eddy currents
magnetic flux
the amount of magnetic field going through a particular area, calculated with $Φ=BAcosθΦ=BAcosθ size 12{Φ= ital "BA""cos"θ} {}$ where $BB size 12{B} {}$ is the magnetic field strength over an area $AA size 12{A} {}$ at an angle $θθ size 12{θ} {}$ with the perpendicular to the area
mutual inductance
how effective a pair of devices are at inducing emfs in each other
peak emf
$emf0=NABωemf0=NABω size 12{"emf" rSub { size 8{0} } = ital "NAB"ω} {}$
phase angle
denoted by $ϕϕ size 12{ϕ} {}$, the amount by which the voltage and current are out of phase with each other in a circuit
power factor
the amount by which the power delivered in the circuit is less than the theoretical maximum of the circuit due to voltage and current being out of phase; calculated by $cosϕcosϕ size 12{"cos"ϕ} {}$
resonant frequency
the frequency at which the impedance in a circuit is at a minimum, and also the frequency at which the circuit would oscillate if not driven by a voltage source; calculated by $f0=12πLCf0=12πLC size 12{f rSub { size 8{0} } = { {1} over {2π sqrt { ital "LC"} } } } {}$
self-inductance
how effective a device is at inducing emf in itself
shock hazard
the term for electrical hazards due to current passing through a human
step-down transformer
a transformer that decreases voltage
step-up transformer
a transformer that increases voltage
thermal hazard
the term for electrical hazards due to overheating
three-wire system
the wiring system used at present for safety reasons, with live, neutral, and ground wires
transformer
a device that transforms voltages from one value to another using induction
transformer equation
the equation showing that the ratio of the secondary to primary voltages in a transformer equals the ratio of the number of loops in their coils; $VsVp=NsNpVsVp=NsNp size 12{ { {V rSub { size 8{s} } } over {V rSub { size 8{p} } } } = { {N rSub { size 8{s} } } over {N rSub { size 8{p} } } } } {}$