Question 5. One 1,5V battery runs a portable MP3 player that draws 5,7mA of current for about six hours before it runs out.
a) What is the resistance If the portable MP3 player?
b) How much power is dissipated in the portable MP3 player?
c) Find the energy delivered by the portable MP3 player?

First, convert the values of the units to S.I units (otherwise the final answer may be wrong):

P.D = 1.5 volts
Current = 5.7 x 10^-3 amps
Time = 21600 seconds

a) To find resistance, you can use the equation V=IR and rearrange it to find the resistance.

Resistance = p.d / current
Resistance = 1.5 / 5.7x10^-3

Resistance = 263.2 ohms (rounded to 1dp)

b) To find power, you can use the following equations to calculate power:
P=VI
P=I^2 R
P = V^2 / R
P = E/T

You can use any of the equations and still get the right answer, however it's best to use the equations which have the values that you already know from the questions.

I used P=VI:

Power = p.d x current
Power = 1.5 x (5.7x^-3)

Power = 8.55 x 10^-3

c) To find energy, you can use the equation E=PT.

Energy = power x time

(Using the value of power from the previous question)

Energy = (8.55x10^-3) x 21600

Energy = 184.68 joules

Hope this helps :)