Question

A p.d. of 10 V is needed to make a current of 0.02 A flow through a wire. What p.d. is needed to make a current of 250 mA flow through the same wire?

Answer 1

Potential difference = 10V

Current = 0.02A

So resistance = V/I

Resistance = 10/0.02

Resistance = 500 ohms.

Current = 250mA = 250 × 10^-3 A

= 0.25A

Resistance = 500 ohms

Potential difference = iR

V = 0.25 × 500

V = 125 volts.

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Answer 2

The 125 V of potential difference is needed to make a current of 250 mA flow through the same wire.

Explanation:

According to the question, there would be two cases:

Firstly, the potential difference, $V_1= 10 V$and current through a wire, $I_1= 0.02 A$

From ohm’s law,

$V= IR$

And we need R to calculate the p.d. , V₂ needed to make a current, $I_2$ of 250 mA through the same wire.

So, $R=\frac{V_{1}}{l_{1}}=\frac{10 V}{0.02 A}=500 \Omega$

Therefore, now for the new p.d., $V_{2}=I_{2} R=250 \times 10^{-3} \mathrm{A} \times 500 \Omega=125 \mathrm{V}$

Hence, 125 V of potential difference is needed to make a current of 250 mA flow through the same wire.