Flashcards in 11.1 Magnetic Flux And Induced EMF Deck (14):

1

## What is magnetic flux?

### The product of the magnetic field through a loop, the area of the loop and the cosine of the angle between the field and the normal to the loop § = BAcos@

2

## What is magnetic flux linkage?

###
The product of the flux through a loop times the number of turns of the wire around the loop. If the loop contains N turns of wire the magnetic flux linkage through the loop

& = N§ = NBAcos@

3

## What is Faraday's law?

### The EMF induced in a loop is equal to the negative of the rate of change of magnetic flux linkage with time emf = - delta$/delta t

4

## What is Lenz's law?

### The direction of the induced EMF is such as to oppose the change in flux that created it. This is a restatement of the law of conservation of energy.

5

## If the field is parallel to the surface what is the flux in the loop?

### Zero.

6

## If the field is normal to the surface what is the flux in the loop?

### Maximum.

7

## If the loop is made of conducting wire what will the emf do?

### Produce a current.

8

## What is the first important application of Faraday's law?

###
The magnetic field strength is increasing with the loop inside the field - to find the rate if change of flux linkage use the formula

delta &/delta t = N(delta B/delta t)A and this also gives the induced EMF.

9

## What is the second important application of Faraday's law?

### A rod is pushed steadily to the right of a magnetic field with speed v so the area of the loop decreases thus decreasing the flux linkage in the loop. The rate of change in flux linkage is delta &/delta t = delta(BLx)/delta t = BL(delta x/delta t) = BLv

10

## What is the third important application of Faraday's law?

### A loop is rotating at a constant angular speed about a vertical axis in a constant magnetic field directed horizontally to the right. The loop rotates about the axis with constant angular speed d@/dt = w = 2pif. Hence @ = 2pift. The flux through the look changes because the angle between the loop and the field changes.

11

## In the applications of Faraday's law how can Lenz's law be introduced?

### It can be used to find the direction of the induced current.

12

## What does Lenz's law state if the flux is increasing?

### The induced current must produce a magnetic field opposite to the external field.

13

## What does Lenz's law state if the flux is decreasing?

### The induced current must produce a magnetic field parallel to the external field.

14