Electromagnetic Induction 2
Physics: AQA A Level, topic 7.5.6
Producing A.C. Using Induction
A coil can be rotated in a magnetic field to produce alternating current (a.c).
Experimental set up
Faraday's Law
- Faraday’s law says that the induced emf is directly proportional to the rate of change of flux linkage.
- The flux linkage through the coil is BAN cosθ.
- For this coil, θ = ωt, where ω = 2πf and f is the frequency of rotation.
- Thus the flux linkage is BAN cos(ωt) and the emf will be directly proportional to BANω sin(ωt).
- Finally, if f is increased, this not only increases the frequency of induced emf, it also increases the amplitude of the induced emf.
Induced Electromotive Force
When a coil is rotating in a magnetic field, the flux linkage is constantly changing. This induces an electromotive force (emf).
A rotating coil
- A coil is made of N turns and has an area A and is rotating at an angular velocity .
- If the coil rotates, it 'cuts' the field lines. This induces an emf.
Calculation
- The equation for the emf induced is:
- Emf induced = field strength x area x number of coils x angular speed x
Test yourself on Electromagnetic Induction 2
If the frequency of the rotation of a coil is increased what happens to the EMF?
What is the effect of increasing the parameter f?
What is the correct equation for the flux linkage?
What is the equation for the emf induced in a rotating coil?
Which of the following would increase the amplitude of an induced emf?