AP Physics C E and M 11.4: Electric Circuit Power

Describe energy transfer into, out of, or within an electric circuit through power, current, potential difference, and resistance.

[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 $\omega$ 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 $\Phi=B A \cos (\omega t)$ .

Figure 1

(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 $0 \leq t \leq T$ .

Figure 3

[ 3 ]

For a curve that starts at the origin and has equal maximum values and equal minimum values
Scoring Note: A curve that starts and ends at P=0 and has a single maximum can earn this point.

(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 $|\varepsilon|$ .

[ 2 ]

\multirow[t]{3}{*}{D} & For correctly indicating whether the representations are consistent in parts A and C & Point D1 \\ \hline & For a correct justification that indicates that the maxima and/or minima of the graph in part C align with the bars drawn in part A because P is proportional to $\mathcal{E}^{2}$ & Point D2 \\ \hline &

Example Response
Yes, part C is consistent with part A. P is proportional to $\mathcal{E}^{2}$ . When $\|\mathcal{E}\|$ is maximum, P is maximum.

& \\ \hline \end{tabular}

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11.4.A—Describe the transfer of energy into, out of, or within an electric circuit, in terms of power question 1

Question (a)

Question (b)