CAIE A-Level Physics A2 19.2.2 W 1 2 Qv 1 2 Cv 2

[Maximum number: 7]

(a)

Two capacitors P and Q are connected in parallel to a power supply of voltage V. The capacitance of P is $200 \mu \mathrm{~F}$ . The capacitance $C_{Q}$ of Q can be varied between 0 and $400 \mu \mathrm{~F}$ . When $C_{Q}=0$ , the total energy stored in the capacitors is 2.5 mJ .

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(i)

Show that the supply voltage V is 5.0 V .

Figure for Question (i) — CAIE A-Level Physics A2

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$E=1 / 2 C V^{2}$ $V=\sqrt{ }\left[\left(2 \times 2.5 \times 10^{-3}\right) /\left(200 \times 10^{-6}\right)\right]=5.0 \mathrm{~V}$

(ii)

Calculate the total energy, in mJ , stored in the capacitors when $C_{\mathrm{Q}}$ has its maximum value.
15
total energy = mJ

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total capacitance $=600 \mu \mathrm{~F}$ $\begin{aligned} E =1 / 2 \times 600 \times 10^{-6} \times 5.0^{2} \left(=7.5 \times 10^{-3} \mathrm{~J}\right) \end{aligned}$ $=7.5 \mathrm{~mJ}$

(iii)

On Fig. 6.2, sketch the variation of the total energy E stored in the capacitors with $C_{\mathrm{Q}}$ , as $C_{Q}$ varies from 0 to $400 \mu \mathrm{~F}$ .

Fig. 6.2

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CAIE A-Level Physics A2 19.2.2 W 1 2 Qv 1 2 Cv 2 Topic Practice

Question 1

Question (a)

Question (i)

Question (ii)

Question (iii)