Question

A 1.4 v d-cell battery is rated at 15,000 ma⋅h. part a for how long could such a battery power a flashlight bulb rated at 1.1 w ?

Answer 1

The current through a 1.1 watts light bulb is given by the equation

`P=U*I \rightarrow I=P/U`
Thus
`I=1.1/1.4=0.786 A`
The capacity of the battery is

`C=15000 mA*h =15 A*h`
In words we say that if a current of 15 A is taken from it, it lasts for 1 hour.
If we take a current I=0.786 A the battery lasts a time of

`t=C/I=15/0.786 =19.1 hours`