Faraday’s Law - General Physcis - Lecture Slides, Slides of Physics

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Faraday’s Law

Area Change

The sliding bar creates an emfby changing the area in themagnetic field.

•^

Constant magnetic field

The potential was due to thetime rate of change of area.

A t B

vBL

V

 







Field Orientation

The emf depends on thechange in field or the changein area.

•^

Area perpendicular to the field

This suggests that the productof the field and areaperpendicular matters.

^

^

^



t AB

B t A

V

      



 cos

Magnetic Flux



The product of the field and area perpendicular to thefield is the

magnetic flux

.



The magnetic flux is measured in webers.

-^

1 Wb = 1 T m

2



The magnetic field can be thought of as a flux density.

 cos AB

M^





A

B

M  

Coil Flux

A circular flat coil has 200turns of wire with a totalresistance of 25

and an

enclosed area of 100 cm

There is a perpendicularmagnetic field of 0.50 T that isturned off in 200 ms.

Find the current induced in thecoil.

This problem has three parts.

To get the current from theresistance the voltage isneeded.

To get the voltage the flux isneeded.

•^

Flux linkage works, too

Find the flux first.

Flux to Current

The magnetic flux is

= BA

•^

= (0.50 T)(100 cm

•^

= (0.50 T)(0.010 m

•^

= 0.0050 T m

2

The change in flux isnegative since it is turnedoff.

The induced emf is

•^

E^

=^

 N

t

•^

E^

= -(200)(-0.0050 Tm

(0.20 s)

-^

E^

=^

 V

= 5.0 V

The induced current comesfrom Ohm’s Law.

•^

I = V/R

•^

I^ = (5.0 V) / (

•^

I^ = 0.20 A

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