Battery Size Alkaline NiCd Nominal Voltage Energy Available

Battery
Size Alkaline   NiCd
Nominal Voltage   Energy Available   Nominal Voltage   Energy Available
AAA   1.5 volts   0.5 watt-hours   1.2 volts   0.2 watt-hours
AA   1.5 volts   1.5 watt-hours   1.2 volts   0.36 watt-hours
C   1.5 volts   5.0 watt-hours   1.2 volts   1.2 watt-hours
D   1.5 volts   15 watt-hours   1.2 volts   3.6 watt-hours

The table above details the nominal cell voltage and energy available for several different sizes and types of batteries. The figure below represents the circuit of a hand-held flashlight. The bulb in the flashlight consumes 8.1 watts.

power_energy_4q.gif

If size AA alkaline batteries have been put in the flashlight, how long will it remain on (in minutes) before the batteries die?

Solution

Ans)

Alkaline AA batteries Vnominal=1.5 V and Watt-hour rating=1.5 watt-hours

As two batteries connected in series Total Watt-hour rating W-H=2*1.5=3 watt-hours

W-H =3 watt-hours

Power of flash light P =8.1 Watts

Time of Flash light will remain=W-H/P=3/8.1=0.37037 hours=0.37037*60=22.22 minutes

So time light will last=22.22 minutes