Question

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

Answer 1

For the bulb,

                  V=220 V

                  P=10 W

                  R=V²/P

                     =220²/10=48400/10 = 4840 ohm

For the circuit,

                   V=220 V

                    I=5 A

                   R=V/I=220/5=44 ohm

1/R1+1/R2+..........................................+1/Rn =1/44

Let n bulbs are connected in parallel

 n/4840=1/44

 n=4840/44

n =110

110 lamps can connected in parallel.

                 

Answer 2

hope this helps you...