Question

A commutator having a diameter of 60 cm rotating at 400 rpm. If the time of commutation of commutator is 1.5 msec, the value of brush width will be ____ cm.

• A. 1.88

Answer 1

The correct option is A 1.88
Given, Speed of rotation = 400 rpm

$=\frac{400}{60}=\frac{20}{3}$ revolution/sec

Peripheral velocity of commutator,

$V_p=\pi DN$

$=\pi \times 60\times \frac{20}{3}cm/sec=400\pi cm/sec$

Also, $V_p\times t_c=\text{Brush width}$

Brush width $=400\pi \times 1.5\times {10}^{-3}=1.88cm$