Question

Physics Prelab: Motors and Generators

a) Explain how you can find the direction of the current if magnetic flux increases as opposed to decreases through a current loop – what is the direction of the resulting current in the loop?

b) What is the voltage induced in a generator with 441 turns, an area of 140 mm² turning at a rate of 47 rpm with a constant field of 0.0727 T?

Answer 1

a)

Use Lens law,

It states that induced magnetic field due the induced current in the coil oposes the change in the magnetic flux.

e=-dф/dt

Since the magnetic flux due to external magnetic field increases, the induced magnetic field is directed opposite of the external magnetic field.

Now use right hand rule.

It states that curl the figures of the right hand around a conductor. The thumb will denote the direction of the direction of the current and the curl fingers will denote the direction of the magnetic field.

Thus, by right hand rule the direction of the current induced in the coil is counterclockwise.

b)

ω=47rpm= 4.911rad/s

emf=-NBAω

Plug values,

emf=-(441*0.0727T*1.4*10^-4m^2*4.911rad/s)

emf=0.022 V