A laboratory power supply provides a constant potential difference

PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials

Problem

V

. A resistor of resistance

R

is first connected across the supply. It is then replaced by another resistor whose resistance is

0.80R

. Assume temperature effects are negligible. (i) Express the initial power

P_{1}

in terms of

V

and

R

. (ii) Derive an expression, in simplest form, for the ratio

\dfrac{P_{2}}{P_{1}}

of the power

P_{2}

dissipated by the second resistor to the initial power

P_{1}

. (iii) Using your result, calculate the percentage change in power when

R

is reduced by

20\%