Question

In: Electrical Engineering

Emergency exit lighting in buildings stores a charge in a battery that is activated in the...

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?

Solutions

Expert Solution

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 .


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