Alternating Current

JEE Main level, single correct, medium

37 of 190

Question 37 of 190

An ACAC source rated 220V,50Hz220V,50Hz is connected to a resistor. The time taken by the current to change from its maximum to the rms value is :

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Answer: (A) 2.5ms2.5ms

i=i0cos⁡(ωt)i={i}_{0}\cos (\omega t)
i=i0i={i}_{0} at t=0t=0
i=i02i=\dfrac{{i}_{0}}{\sqrt{2}} at ωt=π4\omega t=\dfrac{\pi }{4}
t=π4ω=π4(2πf)=18ft=\dfrac{\pi }{4\omega }=\dfrac{\pi }{4(2\pi f)}=\dfrac{1}{8f}
t=1400=2.5mst=\dfrac{1}{400}=2.5ms

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