Question

Calculate the instantaneous value at 60° , average value and RMS value of an alternating current whose peak value is 20 A.

Answer 1

Peak value of current, I = 20 A 

Angle, θ = 60° [θ = ωt] 

(i) Instantaneous value of current,

i = l_m sin ωt = I_m sin θ

= 20 sin 60° = 20 x \(\frac{\sqrt 3}{2}\) = 10√3 = 10 x 1.732 

i = 17.32 A

(ii) Average value of current,

l_av = \(\frac{2I_m}{π}\) = \(\frac{2 \times 20}{3.14}\)

(iii) RMS value of current,

I_RMS = 0.707 I_m

or \(\frac{I_m}{\sqrt2}\) = 0.707 x 20

I_RMS = 14.14 A