(i) Starting from the definition of electric power and the relation between , and ,…

PHYSICS · Subjective · A Level · Physics · Electricity · Electricity

Problem

(i) Starting from the definition of electric power

P

and the relation between

V

I

and

R

, derive an expression for power dissipated in a resistor (a) in terms of

V

and

R

, and (b) in terms of

I

and

R

. (ii) An electric kettle is marked “

1000\,\text W

250\,\text V

”. Calculate (1) the current drawn by the kettle, (2) the resistance of its heating element. (iii) If the supply voltage drops uniformly by

10\%

while the resistance of the element remains unchanged, determine the percentage reduction in the power output of the kettle.