Lenz’s Law, DC Motors and Magnetic Braking – Practice
1) An industrial electric motor has a resistance of 25 Ω and is connected to a 415 V supply. The back emf is equal to 355V when the motor is operating with a normal load.
a) What is the current that passes through the motor when it is first started?
b) What is the current that passes through the motor when it is operating normally?
2) A magnet is dropped down through a copper pipe as shown below and observed to accelerate at less than the acceleration due to gravity. Explain this observation:
1a) 16.2A b) 2.4A