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Five capacitors are connected across a potential difference V ab as shown in Fig

ID: 2132906 • Letter: F

Question

Five capacitors are connected across a potential difference Vab as shown in Figure. Because of the dielectrics used, each capacitor will break down if the potential across it is V=80 V. What should be the value of Vab(with one decimal place) if you reach the break down voltage one of the capacitor.

Five capacitors are connected across a potential difference Vab as shown in Figure. Because of the dielectrics used, each capacitor will break down if the potential across it is V=80 V. What should be the value of Vab (with one decimal place) if you reach the break down voltage one of the capacitor.

Explanation / Answer

The charge on a capacitor is given by Q = CV
Q is the charge, C is the capacitance and V the voltage.

Sine they are all in series they will all have the same charge.

For a given Q, the voltage will be highest across the smallest capacitor.

At break down, the 5uF capacitor will have a charge of 5 * 80 = 400 uC

The voltage on the 10 uF will be 400 / 10 = 40 v
on the 15 uF will be 400 / 15 = 26.67 v
on the 25 uF will be 400 / 25 = 16 v
and on the 45 uF will be 400 / 45 = 8.89 v

The total voltage Vab will be 80 + 40 + 26.67 + 16 + 8.89

= 171.56 volts.