Physics 9702 · AS & A Level · Resistance and resistivity

Resistance and resistivity — practice question

The heater delivers $2.5\,\text{kW}$ when it is connected to a $220\,\text{V}$ supply.
(a(i))[2]

Calculate the heater's resistance.

(a(ii))[3]

The heater uses a wire with cross-sectional area $2.0\times10^{-7}\,\text{m}^2$ and resistivity $1.1\times10^{-6}\,\Omega\text{m}$. Use your answer from (i) to find the wire's length.

(b(i))[1]

The supply voltage is altered to $110\,\text{V}$. Calculate the heater's power output at this voltage, assuming that the wire's resistance does not change.

(b(ii))[2]

State and explain quantitatively one change that could be made to the heater wire so that it gives the same power as in (a).

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: Apply $R=\dfrac{V^2}{P}$ or use $P=IV$ together with $V=IR$

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