Several electric bulbs designed to be used on a 220 V electric supply line

Question 12:

Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?

Solution:

Resistance R₁ of the bulb is given by the expression,

Supply voltage, V = 220 V

Maximum allowable current, I = 5 A

Rating of an electric bulb P=10watts

Because R=V²/P          

 

According to Ohm’s law,

V = I R

Let R is the total resistance of the circuit for x number of electric bulbs

R=V/I

   =220/5=44 Ω

Resistance of each electric bulb, R₁=4840Ω

 

∴ Number of electric bulbs connected in parallel are 110.