Question

what is the magnitude of current that flows across a 9-V battery connected to a resistor 15ohm? how long it will take a charge of 30 C to pass a cross section in a circuit? calculate the power rating.

Answer 1

Given $V = 9V, R = 15\Omega$

Then by ohm's law,

current, $I = \frac{V}{R} = \frac{9}{15} = 0.6A$

Also, $I = \frac{Q}{t} \implies t = \frac{Q}{I}$ $= \frac{30}{0.6} = 50 s$

Power, $P = VI = 9*0.6 = 5.4 W$