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1. Its the very last part of a question stumping me...

"The region of uniform magnetic field is created by the electric current in an arrangement of coils. Suggest how the end of the electron beam is swept up and down the TV screen." 2824 Jan 2007

Im not too sure what this question is asking - any help here will be greatly appreciated.

I dont understand what the markscheme means either;

"Change in direction of magnetic field changes direction of electron beam.
Change in magnitude of current in coil to move the electron beam across"...
2. A moving electron will experience a force in a magnetic field. This force produces a deflection. The magnitude and direction of the force (and hence deflection) depend on the strength and direction of the B field via left hand rule. (It also depends on the speed of the elections but that's usually constant in these questions.)

Varying the current in the coil will change the magnitude of the magnetic field and reversing the current will reverse the field.

That should at least help to explain the markscheme.
3. (Original post by MrToodles4)
Its the very last part of a question stumping me...

"The region of uniform magnetic field is created by the electric current in an arrangement of coils. Suggest how the end of the electron beam is swept up and down the TV screen." 2824 Jan 2007

Im not too sure what this question is asking - any help here will be greatly appreciated.

I dont understand what the markscheme means either;

"Change in direction of magnetic field changes direction of electron beam.
Change in magnitude of current in coil to move the electron beam across"...
The electron beam of a T.V. (old redundant technology Cathode Ray Tube) is focused as a spot onto the phosphorescent coating of the T.V. screen. When the beam strikes, it causes photons to be emitted from that spot.

In order to produce an image, the spot must be scanned across the screen left to right starting at the top of the screen in one corner and progressing downwards in successive lines, rather like the way lines of text are typed and written on a VDU; first from left to right and then the next line left to right etc. until the screen is full of text.

The TV picture is produced in the same way.

The position of the spot is controlled by field coils placed orthogonally to each other (X and Y direction) which deflect the beam as it passes through the magnetic fields generated by the coils.

The magnitude of the current through the coils determines the strength of the filed and hence degree of displacement of the beam from a straight line. i.e. the electrons within the beam are deflected as they progress through each coils magnetic field. (deflection is proportional to the magnitude of the current in each field coil).

The direction of current (polarity) through each coil determines the which way the beam is deflected - left or right or up and down from the reference central position (when no magnetic field is present).

In this way the beam can be scanned across the screen to cover the full surface area of the screen.

The workings of a TV (as described above) used to be covered in the scottish standard grade physics, albeit without the field stuff. I'm not sure if it's still the case but there are still lots of good materials online eg here http://www.kelsohighschool.org.uk/si...unications.pdf - scroll down to p8 for the television bit.

(Note Standard grade is GCSE equivalent, not A-level)

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