Question

A potential difference of 20V is needed to make a current of 0.05A flow through a resistor. What potential difference is needed to make a current of 300 mA flow through the same resistor?

• A. 60V
• B. 120V
• C. 40V
• D. 150V

Answer 1

The correct option is B 120V

Answer is B.
According to Ohm's law, $V=IR$. That is, $R=\frac{V}{I}$.
In this case, the voltage is $20V$ and the current is $0.05A$.
So, the resistance $R=20/0.05=400$ ohms.
Now, to make a current of 300 mA flow through the same resistor of 400 ohms, the potential difference to be applied is calculated as follows.
Here, $I=300mA=0.3A$ and $R=400$ ohms.
Therefore, $V=0.3\times 400=120V$.
Hence, to make a current of 300 mA flow through the same resistor of 400 ohms a potential difference of 120 V is applied.