Question

The polarity of induced e.m.f. in a generator can be reversed by reversing the direction of 
1. Rotation
2. Field flux
3. Rotation and field winding terminals both
4. Either rotation or field winding terminals

Answer 1

Correct Answer - Option 4 : Either rotation or field winding terminals

Induced emf in DC generator is

\(E_g=\frac{ϕ ZNP}{60A}\)

ϕ = Flux per pole

Z = No. of conductors

P = No. of poles

N = Speed in rpm

A = No. of parallel paths

E_g ∝ ϕ N

The polarity of induced e.m.f. in a generator can be reversed by reversing either the direction of rotation or field winding connection.