(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 = 90 o (sin θ = 1),
θ = 0 o (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
Researching deflecting electron beams 20th 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 tube
an 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.
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).