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AP Physics C: Electricity & Magnetism 11.4 Electric Power Questions

Analyse how circuits transfer and dissipate energy by connecting electrical power to current, potential difference, resistance, and time.

Syllabus
Effective Fall 2024
Course
AP Physics C: Electricity & Magnetism

Exam points

  • choose an equivalent power relation from the known current, potential difference, and resistance
  • calculate energy transferred by constant power or integrate power when the circuit varies with time
  • derive the power of a resistor after modelling its current or potential difference
  • compare power dissipation after a switch or series-parallel arrangement changes the circuit
  • relate lightbulb brightness and temperature-dependent resistance to electrical power

Covered syllabus points

11.4.A—Describe the transfer of energy into, out of, or within an electric circuit, in terms of power

Question 1

[Maximum number: 5]

A rotating, circular, conducting loop of area A and resistance R is in an external uniform magnetic field of magnitude B that is directed in the -z-direction. At time t=0, the magnetic field is perpendicular to the plane of the loop, as shown in Figure 1. The loop is rotating with constant angular speed ω\omega and period T about the dashed line that is along the diameter of the loop. The value of the magnetic flux through the loop as a function of time t is Φ=BAcos⁡(ωt)\Phi=B A \cos (\omega t).

Figure 1

Figure 1

Question (a)

(a)

On the axes shown in Figure 3, sketch a graph of the instantaneous power P dissipated by the loop as a function of t during the time interval 0≤t≤T0 \leq t \leq T.

Figure 3

Figure 3

[ 3 ]

Question (b)

(b)

Indicate whether the sketch you drew in part C is or is not consistent with the bars that you drew in part A. Briefly justify your answer by referencing the functional dependence between P and ∣ε∣|\varepsilon|.

[ 2 ]
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