ELECTROMAGNETIC EFFECTS
description
Transcript of ELECTROMAGNETIC EFFECTS
![Page 1: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/1.jpg)
ELECTROMAGNETIC EFFECTS
![Page 2: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/2.jpg)
1. 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 = Bilsinθ
This is the basis of electric motors and analogue electric meters.
THE MOTOR EFFECT
![Page 3: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/3.jpg)
![Page 4: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/4.jpg)
CATHODE RAY TUBES
![Page 5: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/5.jpg)
![Page 6: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/6.jpg)
![Page 7: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/7.jpg)
![Page 8: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/8.jpg)
![Page 9: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/9.jpg)
![Page 10: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/10.jpg)
This is the basis of the old cathode ray tube TV’s and computer monitors (and oscilloscopes). F = qvBsinθ
Free charges also experience a force in a magnetic field.
![Page 11: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/11.jpg)
![Page 12: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/12.jpg)
Moving a wire in a magnetic field can produce a voltage in the wire, and thus a current. Moving a magnet around a wire does the same thing.
Key concept: if the flux (amount of magnetic flow or amount of magnetic field lines) changes around a conductor, then a voltage is produced across the ends of the conductor.
Φ = B A cosθ
Electromagnetic induction
![Page 13: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/13.jpg)
The faster the flux changes, the higher the voltage.
There will be opposition to flux change. As we change flux, a voltage (emf) is generated in the wire, that opposes the change we are making. (Lenz’ Law).
Every loop of wire exposed to a changing flux experiences its own emf across its ends. If the loops are in series, we add the emfs.
![Page 14: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/14.jpg)
All together,
![Page 15: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/15.jpg)
These concepts of changing flux associated with a wire are used in electric generators.
![Page 16: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/16.jpg)
The voltage produced (and so also the current) will be an alternating current (AC).
![Page 17: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/17.jpg)
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
![Page 18: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/18.jpg)
![Page 19: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/19.jpg)
![Page 20: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/20.jpg)
![Page 21: ELECTROMAGNETIC EFFECTS](https://reader035.fdocuments.in/reader035/viewer/2022062813/56816479550346895dd65e18/html5/thumbnails/21.jpg)
A last look at electric motors: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.