# Does a TV need to be protected from the Earth's magnetic field?

1. Jun 5, 2009

### alycel3

You've just learned about the earth's magnetic field and how a compass works and
you are relaxing in front of the TV. Tired of your show, you think about how the picture tube works in relation to what you have learned. In a typical color picture tube for a TV, the electrons are boiled off of a cathode at the back of the tube and are accelerated through about 20,000 volts towards the picture tube screen. On the screen is a grid of color dots'' about 1/100 inch apart. When the electrons hit them, the dots scintillate their appropriate colors producing the color picture. Without taking apart the set, you determine whether the manufacturer needed to shield the color picture tube from the earth's magnetic field?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 5, 2009

### xepma

Yea, I think that mostly the older tv's have this 'problem', and in that case the tv is adjusted to compensate for the effect.

Try putting your tv upside down. In that case the orientation of the magnetic field is the wrong way, so the picture comes out wrong.

3. Jun 5, 2009

### Dick

I think the point might be to calculate the deflection of the beam due to the Earth's magnetic field and see if it's as large as 1/100 inch rather than proposing a physical experiment. Just a guess.

4. Jun 6, 2009

### xepma

No, this is more fun ;)

5. Jun 7, 2009

### Naty1

Look up the strength and direction of the earth's magnetic field at the altitude of your choice...see if it deflects an electron over a distance of a foot or two enough to make a difference in it's trajectory.....F = qv x B, etc...