ELECTROMAGNETIC EFFECTS. THE MOTOR EFFECT. Current-carrying wires in an external magnetic field experience a force, dependent on B, I, l and the angle between wire and B field. F = Bilsin θ This is the basis of electric motors and analogue electric meters. CATHODE RAY TUBES.
F = Bilsinθ
This is the basis of electric motors and analogue electric meters.
Φ = B A cosθ
These concepts of changing flux associated with a wire are used in electric generators.
The voltage produced (and so also the current) will be an alternating current (AC).
Generators must supply power to distant places. How is this done? To reduce heat losses, it is better to send the electric current with a low I and high V, rather than high I and low V. To do this a transformer is needed.
Vp/Vs = Np/Ns
VpIp = VsIs
When a motor starts up, lights often dim. Why is this?
When the motor starts, there is a maximum current flow due to the high emf across the motor. As the motor speeds up, a back emf is induced (coils rotating in a magnetic field) in the coils, that opposes the forward emf. The back emf reaches a maximum when the motor is turning at full speed. This reduces the overall emf across the motor. The current is also reduced, and the lights elsewhere get more current again.