Chapter 20 Electromagnetic Induction. Electricity and magnetism Generators, motors, and...
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Transcript of Chapter 20 Electromagnetic Induction. Electricity and magnetism Generators, motors, and...
Chapter 20
Electromagnetic Induction
Electromagnetic Induction
• Electricity and magnetism• Generators, motors, and transformers
Current
Previously, we said three things were required for a current to flow in a circuit:
1. Potential difference2. Closed circuit3. Charges free to move
Electromagnetic Induction
electromagnetic induction = the process of creating a current in a circuit loop by changing the magnetic field that passes through the circuit
(Inducing an emf)
Linear Induction Flashlight / Faraday Flashlight / “Shake Flashlight”
Lenz’s LawLenz’s Law describes the rule for finding the direction of the induced current:
Note: the field of the induced current does not oppose the applied field, but the change in the applied field (so that the total field strength remains constant).
The magnetic field of the induced current is in a direction to produce a field that
opposes the change causing it.
Circuit is moved into the magnetic field
Circuit is rotated in the magnetic field
Intensity of the magnetic field is varied
Magnetic Flux
magnetic flux = the number of field lines that cross a certain area at right angles to that area
Units: Weber (Wb)
ΦM=𝐴𝐵cos 𝜃(magnetic field)(surface area)×
magnetic flux =
(cosine of the angle between B and the normal to the plane of the loop)
×
Faraday’s Law of Magnetic Induction
For a single loop,
* Minus sign indicates the polarity of the induced emf (reflects Lenz’s Law)
𝑒𝑚𝑓=−ΔΦ𝑀
Δ𝑡
PracticeA circuit is stretched over a period of 0.25 seconds in a magnetic field of 0.050 T. The circuit dimensions change from 4.0 m x 4.0 m to 2.0 m x 6.0 m, as shown below. Determine the emf induced in the circuit.
�⃗�
start end
4.0 m
4.0 m 6.0 m
2.0 m
Faraday’s Law of Magnetic Induction
For multiple loops,
N = the number of loops in the circuit
𝑒𝑚𝑓=−𝑁ΔΦ𝑀
Δ𝑡
PracticeA coil with 25 turns of wire is wrapped around a hollow tube with an area of 1.8 m2. Each turn has the same area as the tube. A uniform magnetic field is applied at a right angle to the plane of the coil. If the field increases uniformly from 0.00 T to 0.55 T in 0.85 s, find the magnitude of the induced emf in the coil. If the resistance in the coil is 2.5 Ω, find the magnitude and direction of the induced current in the coil.