Chapter 20, Problem 57P

To determine

That factor of change in output torque.

Answer to Problem 57P

The output torque also drops by 12% .

Explanation of Solution

Given:

The current in the motor decreases by $12\%$ .

Formula used:

The torque of a coil having N loops in a magnetic field is given by,

  $\tau =NIAB$

Here,

I is the current

A is the area of coil

B is the magnetic field strength.

Calculation:

From the above equation, it is observed that the torque is proportional to the current.

  $\tau \propto I$

So, if current decreases by $12\%$ then torque will also decrease by 12%.

The $100-12\%=88\%$ of the original one or $0.88$ times.

Conclusion:

The output torque reduces by 12%.