4.5.1 Electromagnetic induction (3)
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1.
A coil of wire is moved rapidly into and out of a magnetic field. Explain, using the concept of an induced e.m.f., why this movement causes a current to flow in the coil. Include a diagram to illustrate your answer.
When a coil of wire moves through a magnetic field, the magnetic flux linked with the coil changes. This change in magnetic flux induces an electromotive force (e.m.f.) in the coil. According to Faraday's Law of Induction, the induced e.m.f. opposes the change in magnetic flux that caused it.
As the coil moves into the magnetic field, the magnetic flux increases, inducing a positive e.m.f. As the coil moves out of the magnetic field, the magnetic flux decreases, inducing a negative e.m.f. This induced e.m.f. drives a current through the coil. The direction of the induced current is such that it opposes the change in flux. This is described by Lenz's Law.
Diagram:
[Image missing: Diagram of a coil moving into and out of a magnetic field]
2.
A magnet is moved towards a coil of wire. Explain how this movement causes an electric current to flow in the coil. Describe the direction of the induced current using Fleming's Left-Hand Rule.
Explanation of Induced Current:
When a magnet is moved towards a coil of wire, the magnetic flux through the coil changes. This change in magnetic flux induces an electromotive force (EMF) in the coil, according to Faraday's Law of Electromagnetic Induction. This EMF drives a current through the coil. The magnitude of the induced EMF is proportional to the rate of change of magnetic flux and the number of turns in the coil.
Fleming's Left-Hand Rule:
To determine the direction of the induced current:
- Point your thumb in the direction of the induced current.
- Point your index finger in the direction of the motion of the magnet towards the coil.
- Your middle finger will point in the direction of the induced current in the coil.
3.
A simple coil of wire is used to generate an e.m.f. A bar magnet is moved towards the coil. Describe how the magnitude of the induced e.m.f. changes as the magnet approaches the coil. Explain your answer in terms of Faraday's Law of Induction.
As the bar magnet approaches the coil, the magnitude of the induced e.m.f. increases. This is because:
- The magnetic flux through the coil increases as the magnet gets closer. The magnetic flux is proportional to the area of the coil and the strength of the magnetic field, both of which increase as the magnet approaches.
- The rate of change of magnetic flux (dΦ/dt) increases as the magnet approaches. The closer the magnet, the faster the magnetic field lines are cutting across the coil's area, leading to a greater rate of change of flux.
According to Faraday's Law of Induction, the induced e.m.f. is proportional to the rate of change of magnetic flux. Therefore, as the rate of change of magnetic flux increases, the magnitude of the induced e.m.f. also increases.