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EEJ MAIN Physics QUESTION #6987
Question 1

Two capacitors $C_1$ and $C_2$ are charged to 120 V and 200 V respectively. When connected together, the potential on each becomes zero. Which relation holds?

  • $5C_1 = 3C_2$
  • $3C_1 = 5C_2$✔️
  • $3C_1 + 5C_2 = 0$
  • $9C_1 = 4C_2$
Correct Answer Explanation

For the potential to become zero after connection, the total charge must be zero (charges cancel). Taking signs into account:

$Q_1 - Q_2 = 0 \Rightarrow C_1 \times 120 = C_2 \times 200$

$\frac{C_1}{C_2} = \frac{200}{120} = \frac{5}{3}$

$\Rightarrow 3C_1 = 5C_2$

The capacitors must have been charged with opposite polarities so that when connected, charges cancel. Conservation of charge gives $120C_1 = 200C_2$, yielding $3C_1 = 5C_2$.