Question

If each of the two headlights uses 40 W and each of the two taillights 4 W , for a total of 88 W , how long will a fresh 12-V battery last if it is rated at 90 A⋅h ? Assume the full 12 V appears across each bulb. Express your answer using two significant figures.

Answer 1

12.27 h

Step-by-step explanation:

Total power consumption by the car = 88 W

It has a battery of 12V and rating 90 A-h.

The full 12V appears across each bulb. We know that power is given by

`P=Vi`

where,
`i` is the current flowing through the circuit.

So, in this case,

`i=(P)/(V)=(88)/(12)A=7.3333A`

The rating in units of A-h is the amount of energy available in a battery that will allow a current of 1 A to flow in a circuit for 1 hour.

Naturally, the time for which the battery will last =
`(90)/(7.3333)h=12.27h`