Question

You are camping in the wilderness. After a few days, you are horrified to discover that you did not pack as many batteries as you had planned, and you have no working batteries for your lights at night. Rummaging through the spare parts in the back of your truck, you find an old motor. On the plate, the information claims that the motor operates from 120 V, rotating at 1,600 rev/min, with an average back emf of 80.0 V. You wish to use the motor as a generator to provide a voltage with a peak value of 7.50 V to operate your electric lantern. You attach a hand crank to the armature of the motor. You need to determine the angular speed (in rev/s) at which you must rotate the crank to provide the desired voltage. Model the armature as a flat coil of wire. Notice that the average back emf is provided, not the peak value, so you will need to find an expression for the average back emf of a motor in terms of parameters associated with the armature rev/s Need Help?

Answer 1

Answer:

Angular speed = 2.5 rev/sec

Explanation:

εo= 80 V

wo = 1600 rev/min

ε = 7 V

εo=BANwo..........(1)

ε=BANw..............(2)

Dividing equation (1) by (2) we get,

εo/ε =wo/w

Or, w=εwo/εo

By putting values we get,

w= 1600×7.5/80

w = 150 rev/min

Or, w= 2.5 rev/sec

So,

Angular speed = 2.5 rev/sec.