Electromagnetic Induction and Alternating Current 6 Question 2

2. An alternating voltage V(t)=220sin100πt volt is applied to a purely resistive load of 50Ω. The time taken for the current to rise from half of the peak value to the peak value is

(a) 5ms

(b) 2.2ms

(c) 7.2ms

(d) 3.3ms

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Answer:

Correct Answer: 2. (d)

Solution:

  1. In an AC resistive circuit, current and voltage are in phase.

 So, I=VRI=22050sin(100πt)

Time period of one complete cycle of current is

T=2πω=2π100π=150s

So, current reaches its maximum value at

t1=T4=1200s

When current is half of its maximum value, then from Eq. (i), we have

I=Imax2=Imaxsin(100πt2)

sin(100πt2)=12100πt2=5π6

So, instantaneous time at which current is half of maximum value is t2=1120s

Hence, time duration in which current reaches half of its maximum value after reaching maximum value is

Δt=t2t1=11201200=1300s=3.3ms



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