A coil of inductance 0.50 H and resistance 100 W is connected to a 240 V, 50 Hz A.C. supply.

(a) What is the maximum current in the coil?


(b) What is the time lag between the voltage maximum and the current maximum?

Given: Inductance = 0.50 H

Resistance R = 100 Ω


Voltage V = 240 V


Frequency = 50 Hz


The diagram is:



(a) Peak voltage is given by the following formula:


V0 = √2 V


V0 = √2 × 240V


On calculating, we get


V0 = 339.41 V


Angular frequency is given by the formula ω = 2πv


Substituting value of v in above formula


ω = 2 × π × 50(Hz) = 100 π rad/s.


The maximum current in the coil can be calculated as follows:




On calculating, we get


I0 = 1.82 A


(b) The equation for voltage and current are as follows:


V = V0 cos ωt


I = I0 cos (ωt-Ф)


At time t = 0, V = V0


At t = Ф/ ω, I = I0


Therefore, the time lag between maximum current and maximum voltage is Ф/ ω. Phase angle is given by the following relation:


tan Ф = ωL/R


tan Ф = (2 π × 50(Hz) × 0.5(H))/100


On calculating, we get


tan Ф = 1.57


or Ф = 57.50


in rad Ф = 57.5π/180 rad


ωt = 57.5π/180


or


On calculating, we get


t = 3.2 ms


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