Question

A motor with a brush-and-commutator arrangement has a circular coil with radius 2.5cm and 150 turns of wire. The magnetic field has magnitude 0.060T and the coil rotates at 440rev/min.
Part A
What is the Maxium emf induced in the coi?
Express your answer using two significant figure.
Emax = V
Part B
What is the average back emf?
Express you anser using two significant figures.
Eav = V

Answer 1

Answer:

(a) 0.81 V

(b) 0.52 V

Explanation:

Number of turns, N = 150

Radius, r = 2.5 cm = 0.025 m

Magnetic field, B = 0.060 T

f = 440 rev/min = 440 / 60 = 7.33 rps

A.

The maximum emf is given by

e = N x B x A x 2 x π x f

e = 150 x 0.060 x 3.14 x 0.025 x 0.025 x 2 x 3.14 x 7.33

e = 0.81 V

B.

The back emf is given by

e' = 2e / π = 2 x 0.81 / 3.14 = 0.52 V