Question 45: Electrostatics & Capacitance

Question

Two capacitors $\mathrm{C}_1$ and $\mathrm{C}_2$ are charged to 100 V and 120 V respectively. It is found that upon connecting them together in parallel, the potential on each one of them is zero. Therefore

Accepted Answer

When the two capacitors end up at zero volts in parallel, their charges must exactly cancel:
Initial charges (taking one capacitorÃ¢ÂÂs polarity as +):
Ã¢ÂÂ¢ QÃ¢ÂÂ = CÃ¢ÂÂÃÂ·100 V
Ã¢ÂÂ¢ QÃ¢ÂÂ = CÃ¢ÂÂÃÂ·(Ã¢ÂÂ120 V)
Conservation of charge gives
$$QÃ¢ÂÂ + QÃ¢ÂÂ = 0 \quad\Longrightarrow\quad CÃ¢ÂÂ\cdot100 \;-\; CÃ¢ÂÂ\cdot120 = 0$$
Divide by 20:
$$5\,CÃ¢ÂÂ = 6\,CÃ¢ÂÂ$$
That is Option D.

Answer

$\mathrm{C}_1+3 \mathrm{C}_2=0$

Answer

$5 \mathrm{C}_1=3 \mathrm{C}_2$

Answer

$5 \mathrm{C}_1+6 \mathrm{C}_2=0$

Answer

$5 \mathrm{C}_1=6 \mathrm{C}_2$

Electrostatics & Capacitance

Two capacitors \mathrm{C}_1 and \mathrm{C}_2 are charged to 100 V and 120 V respectively. It is found that upon connecting them together in parallel, the potential on each one of them is zero. Therefore

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