Electron beams

Your Learning

Write an explanation of how a motor works Including

Magnetic fields (of the wire and magnet)

Force on a wire F = BIL (what affect the speed of the motor)

Flemings left hand rule(how does this help you know which way it is going to go)

 

How much force does a wire feel?

Force = B-field x Current x length of wire F = BIl

The Force is greatest when perpendicular to the magnetic field and zero when parallel

F = BIL sin θ θ = 90o (sin θ = 1),θ = 0o (sin θ = 0),

B = F/IL

Force (Newtons)B- field (Teslas)Current (Amps)Length (metres)

What we are going to do today

• What happens to charged particles in a magnetic field?

• Why does a force act on a wire in a magnetic field when a current flows along the wire?

• What equation can we use to find the force on a moving charge?

The Deflection tube…a basic CRO

Thermionic emission

When energy is given to a wire it heats up but…..

…it can also give off electrons

This is the basis of the electron gun...

• Electrons ‘boil off’ here

They are accelerated here

There is a current here…. And a vacuum here

And a large accelerating +Voltage V here

Applying a magnetic field

circle if vperpendicularto B

spiral in adissipativemedium

helix if component ofv parallel to B

Fv

B

Researching deflecting electron beams20th Century Technology Exhibition

Nowadays most new televisions and computer monitors use LCD displays, but not so long ago they all used picture tubes. In fact,

picture tubes were the main use of electron beams.Vanita and Dave are planning a museum exhibition of technology from

the last century. They will provide a straight forward explanation to help people to understand how each exhibit worked. The electron

beams section of the exhibition has:

a television picture tubean oscilloscopean x-ray tube.

Your task is to write a straight forward, concise explanation of each section, and include pictures that will develop peoples understanding

of the uses of deflecting electron beams.

Hall Probes

• As electrons move through a piece of n-type semiconductor through which a magnetic field passes, then the electrons experience a force (Fleming's left hand rule) which moves them to one side of the semiconductor slab. An electric field builds up giving a force in the opposite direction. (and creating a measurable potential difference).

Electron

Electron+ + + + + +

B- field