An electric bulb is rated as 50 W, 220 V. Calculate the energy consumed by the bulb in 20 minutes. Express your answer in commercial units of electric energy.
Power of the bulb, P = 50 W =
Time, t = 20 minutes =
Energy consumed
Energy consumed by the 100 watt bulb everyday working 2 hours
Energy consumed by four 40 watt bulb every day working 4 hours
Total energy consumed every day
= 0.2 + 0.64 = 0.84 kWh
Total energy consumed in 30 days
= 0.84 x 30 = 25.2 kWh. Ans.
For a heater rated at 4 kW and 220 V, calculate:
(i) the current;
(ii) the resistance of the heater;
(iii) the energy consumed in 2 hours; and
(iv) the cost if 1 kWh is priced at Rs 1.50.
Two lamps, one rated 60 W at 220 V and other 40 W at 220 V, are connected in parallel to electric supply at 220 V.
(a) Draw the circuit diagram to show the connections.
(b) Calculate the current drawn from the electric supply.
(c) Calculate the total energy consumed by the two lamp together when they operate for one hour.
An electrical heater is used on a 220 V supply and takes a current of 5 A
(i) What is its power?
(ii) What is the cost of using the heater for 50 hours if 1 kWh costs Rs 1.50?
(i) Given,
Potential of electrical supply, V = 220 V
Current drawn by electric heater, I = 5 A
Power, P = VI = 220 x 5 = 1100 W.
(ii)
Power,
Energy consumed = P x t
= 1.1 kW x 50 h
= 55 kWh
Cost at the rate of Rs 1.50 per kWh = 55 x 1.50
= Rs 82.50.
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