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.

12.27 h

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

where, is the current flowing through the circuit.

So, in this case,

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 =

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