An electric lamp of 100 Ohms, a toaster of resistance 50 Ohms, and a water filter of resistance 500 Ohms are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current?

Given parameters:

  • Resistance of electric lamp (R1) = 100 Ω
  • Resistance of toaster (R2) = 50 Ω
  • Resistance of water filter (R3) = 500 Ω
  • A potential difference of the source (V) = 220 V

To find:

  • The flow of electric current through the electric iron.
  • Resistance of an electric iron

The three resistors are connected in parallel as shown – 

All 3 resistances are connected in parallel

Solution:
1) The total resistance (R) can be calculated by – 

1/R = 1/R1 + 1/R2 + 1/R3

1/R = 1/100  + 1/50 + 1/500

1/R = (5 + 10 + 1)/500

1/R = 16/500

Total Resistance (R) = 500/16 = 31.25 Ω

2) According to Ohm’s law, the current through a conductor is directly proportional to the voltage across two points of a conductor.

V = IR

Where R is constant called resistance.

R = V/I

I = 220 × (16/500)

I = 7.04 A

Therefore, the resistance of the electric iron is 31.25 Ω and the current flowing through it is 7.04 A.


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