Several electric bulbs designed to be used on a 220 V electric supply line are rated 10 W each. How many bulbs can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A ?
First we will calculate the resistance R of one bulb.
Therefore, resistance of one bulb is 4840
We will now calculate the total resistance of the circuit by using Ohm’s Law:
Thus, the total resistance of the circuit is 44.
Now, we need to find out the number of 4840 bulbs should be connected in parallel to obtain a total resistance of 44. Suppose the number of 4840 bulbs required is x. Then:
Thus, 110 bulbs can be connected in parallel in this circuit.
Explain the following:
(a) Why is the tungsten used almost exclusively for the filament of electric lamps?
(b) Why are the conductors of electric heating devices such as bread toasters and electric irons made of an alloy rather than a pure metal ?
(c) Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its area of cross-section?
(e) Why are copper and aluminium wires usually employed for electricity transmission?