Question

If rotational velocity of a dynamo armature is doubled, then induced emf will become...... What is increased in step down transformer? 

(a) Half 

(b) Two times 

(c) Four times 

(d) Unchanged

Answer 1

The correct option (b) Two times 

Explanation:

emf induced = e = E_o sin ωt

rotational velocity is double i.e ω changes to 2 ω then

e' = E_o sin 2ωt

= 2 E_o sin 2ωt ∙ cos ωt

= 2e cos ωt

= 2e sin[ωt + (π/2)]

If we consider magnitude then e' = 2e i.e. induced emf is twice.