Оценка 5

Оценка 5
ppt
08.05.2020

## Electromagnetic Induction and

Electromagnetic Induction and Faraday’s Law. Lenz's law

## 10.4.2.1 – to explain the occurrence of electromotive force when changing the magnetic flux; 10.4.2.2 – to explain the Lentz's law; Lesson Objectives

10.4.2.1 – to explain the occurrence of electromotive force when changing the magnetic flux;
10.4.2.2 – to explain the Lentz's law;

Lesson Objectives

## Course of the lesson Electromagnetism

Course of the lesson

Electromagnetism
Lenz’ Law
Applications

## Just Do and Observe!

Just Do and Observe!

## Spring 2008 5 Induced Current The next part of the story is that a changing magnetic field produces an electric current in a loop surrounding…

Spring 2008

5

Induced Current

The next part of the story is that a changing magnetic field produces an electric current in a loop surrounding the field
called electromagnetic induction, or Faraday’s Law

## Faraday’s Law of Induction; Lenz’s

Faraday’s Law of Induction; Lenz’s Law

The induced emf in a wire loop is proportional to the rate of change of magnetic flux through the loop.
Magnetic flux:

(on formula sheet)

Unit of magnetic flux: weber, Wb.
1 Wb = 1 T·m2

## This drawing shows the variables in the flux equation:

This drawing shows the variables in the flux equation:

Faraday’s Law of Induction; Lenz’s Law

## Faraday’s law of induction: [1 loop] (on formula sheet) [N loops]

[1 loop]
(on formula sheet)

[N loops]

Faraday’s Law of Induction; Lenz’s Law

8-May-20

11

## The minus sign gives the direction of the induced

The minus sign gives the direction of the induced Emf:
An induced Emf always gives rise to a current whose magnetic field opposes the original change in flux (Lenz’s Law).

Faraday’s Law of Induction; Lenz’s Law

## In (a) the magnetic field and flux are increasing

In (a) the magnetic field and flux are increasing. The current moves in the direction to oppose that – to decrease the magnetic field.
In (b) the magnetic field and flux are decreasing. Again, the current moves in the direction to oppose that.
In (c) there is no change in flux, so there is no induced emf.

## Induced EMF Therefore, a changing magnetic field induces an

Induced EMF

Therefore, a changing magnetic field induces an Emf.
(Faraday’s experiment used a magnetic field that was changing because the current producing it was changing;
the previous graphic shows a magnetic field that is changing because the magnet is moving.)

## Magnetic flux will change if the area of the loop changes:

Magnetic flux will change if the area of the loop changes:

Faraday’s Law of Induction; Lenz’s Law

Current increases in the direction shown (clockwise) to maintain original flux.

## Magnetic flux will change if the angle between the loop and the field changes:

Magnetic flux will change if the angle between the loop and the field changes:

Faraday’s Law of Induction; Lenz’s Law

Flux is decreasing so the current will go in the clockwise direction to increase flux.

## Problem Solving: Lenz’s Law Determine whether the magnetic flux is increasing, decreasing, or unchanged

Problem Solving: Lenz’s Law
Determine whether the magnetic flux is increasing, decreasing, or unchanged.
The magnetic field due to the induced current points in the opposite direction to the original field if the flux is increasing; in the same direction if it is decreasing; and is zero if the flux is not changing.
Use the right-hand rule to determine the direction of the current.
Remember that the external field and the field due to the induced current are different.

Faraday’s Law of Induction; Lenz’s Law

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