Question

The current in the circuit shown below is 1 Amp when the switch is open.
How is the current affected when the switch is closed?

• A. The current remains the same.
• B. The current doubles.
• C. The current decreases by a small amount.
• D. The current increases a small amount.

Answer 1

Answer: (D)

The current increases a small amount.

When the switch is open, no current will flow through $30\Omega$ resistor. Thus 1 A current will flow through both $15\Omega$ resistors.

By ohm's law, $V=(15+15)\left(1\right)$ or $V=30V$

When the switch is closed, $30\Omega$ resistor will be active.

Thus, equivalent resistance , $R_{eq}=15+\frac{15\times 30}{15+30}=25\Omega$

Now the current is $I=30/25=1.2A,$

Thus, the current will increase by small amount when switch is closed.

Hence, option D will correct.