Question

A resistance of 40 Ω is connected to a source of alternating current rated 220 V, 50 Hz. Find the time taken by the current to change from its maximum value to the rms value :

• A. 2.5 ms
• B. 1.25 ms
• C. 2.5 s
• D. 0.25 s

Answer 1

The Correct Option is A

I = I₀cos(ωt) say
⇒ At maximum ωt₁ = 0 or t₁ = 0
Then at rms value
l=l₀l√2
⇒ ωt₂ = \(\frac{\pi}{4}\)
⇒ ω(t₂ – t₁) = \(\frac{\pi}{4}\)
Δt=\(\frac{\pi}{4}\)ω=\(\frac{\pi T}{4}\)×2π
=\(\frac{1}{400}\) s or 2.5 ms
The correct option is (A) :  2.5 ms