Question

(i) A rectangular coil of copper wires is rotated in a magnetic field. In how much revolution, the direction of induced current changes once? 

(ii) An electric lamp of 100Ω, a toaster of resistance 50Ω, and a water filter of resistance 500Ω are connected in parallel to a 220V source. What is the resistance of an electric iron connected to same source that takes as much current as all three appliances, and what is the current through it?

Answer 1

(i) The direction of induced current changes once after every half revolution. 

(ii)The three resistors are connected in parallel as shown:

\(\frac{1}{Req}\)= \(\frac{1}{R_1}\) + \(\frac{1}{R_2}\)+ \(\frac{1}{R_3}\) =\(\frac{1}{100}\) + \(\frac{1}{50}\) + \(\frac{1}{500}\)  

= \(\frac{5+10+1}{500}\)

∴  R_eq = \(\frac{500}{16}\) Ω = 31.25 Ω 

Also, I = \(\frac{V}{R}\) (from ohm’s law) 

= 220 x \(\frac{16}{500}\)= 7.04 A. 

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