(a) Determine the p.d. across a 2 μF capacitor when charged with 5mC (b) Find the charge on a 50 pF capacitor when the voltage applied to it is 0.3 kV.
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ELECTRICAL AND ELECTRONIC PRINCIPLES AND TECHNOLOGY
2ND. EDITION
(a) Determine the p.d. across a 4 µF capacitor when charged with 5 mC (b) Find the charge on a 50 pF capacitor when the voltage applied to it is 2 kV.
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(a) C = 4\, µF = 4 \times 10^{-6}\, FC=4µF=4×10
−6
F and Q = 5\, mC = 5 \times 10^{-3}\, CQ=5mC=5×10
−3
C.
Since C=\frac{Q}{V}C=
V
Q
then V=\frac{Q}{C}=\frac{5\times 10^{-3}}{4\times 10^{-6}}V=
C
Q
=
4×10
−6
5×10
−3
=\frac{5\times 10^{6}}{4\times 10^{3}}=\frac{5000}{4}
4×10
3
5×10
6
=
4
5000
\textbf{Hence p.d. V = 1250 V or 1.25 kV}Hence p.d. V = 1250 V or 1.25 kV
(b) C = 50\, pF = 50 \times 10^{-12}\, FC=50pF=50×10
−12
F and V = 2\, kV = 2000\, VV=2kV=2000V
Q = CV = 50 \times 10^{-12}\times 2000Q=CV=50×10
−12
×2000
=\frac{5\times 2}{10^{8}}=0.1\times 10^{-6}
10
8
5×2
=0.1×10
−6
Hence, charge Q = 0.1\, µCQ=0.1µC