In: Electrical Engineering
Emergency exit lighting in buildings stores a charge in a battery that is activated in the event of a power failure. How much charge is needed to light a single exit sign with a 40 W light bulb for 10 hours?
GIVEN, LIGHT BULB CONSUMES 40W AND IS REQUIRED TO GLOW FOR 10 HOURS.
THEREFORE TOTAL ENERGY CONSUMPTION = POWER x TIME= 40 W x 10 hr = 400 Wh = 400 watt-hour
ASSUMING THE LIGHT BULB RUNS ON STANDARD 12V DC SUPPLY.
THEREFORE TOTAL CHARGE NEEDED TO LIGHT THE BULB FOR 10 HOURS IS GIVEN BY,
CHARGE NEEDED = TOTAL ENERGY CONSUMPTION / VOLTAGE ACROSS BULB
= 400 Wh / 12 V
= 33.33 Ah
=33.33 ampere-hour
thus, 33.33 Ah IS THE AMOUNT OF ENERGY CHARGE REQUIRED IN THE BATTERY TO LIGHT THE(12 VOLT) BULB FOR 10 HOURS .