CAIE A-Level Physics A2 21.1.3 The Fact That the Mean Power in a Resistive Load Is Half the Maximum Power

[Maximum number: 5]

An ideal transformer is shown in Fig.9.1.

Fig. 9.1

(a)

A resistor is connected between the output terminals of the secondary coil. The mean power dissipated in the resistor is 1.2 W . It may be assumed that the varying voltage across the resistor is equal to the varying e.m.f. E shown in Fig. 9.2.

[ 5 ]

(i)

Calculate the resistance of the resistor.

resistance =

$\Omega$

[ 2 ]

either

mean power $=V^{2} / 2 R$ and $V=52(\mathrm{~V})$ $\begin{aligned} R =52^{2} /(2 \times 1.2) =1100(1127) \Omega \end{aligned}$
or

mean power $=V^{2} / R$ and $V=52 / \sqrt{2}(=36.8 \mathrm{~V})$ $\begin{aligned} R =36.8^{2} / 1.2 =1100 \Omega \end{aligned}$

(ii)

On Fig.9.3, sketch the variation with time t of the power P dissipated in the resistor for t=0 to $t=22.5 \mathrm{~ms}$ .

Fig. 9.3

[ 3 ]

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CAIE A-Level Physics A2 21.1.3 The Fact That the Mean Power in a Resistive Load Is Half the Maximum Power Topic Practice

Question 1

Question (a)

Question (i)

Question (ii)