Question

The old TVs accelerate electrons towards the screen through potential differences of thousands of volts over just a few centimeters. Once the electrons are accelerated, they are somehow bent towards different parts of the screen to make up the picture. I once opened one of these TVs to investigate in detail. I found imprinted “5500V” on a part that looked like two capacitor plates, indicating that a potential difference of 5500V is maintained between these capacitor plates. Definitely do not open your TV while it is plugged in! I also measured that the distance that was used for the acceleration of the electrons was 1.5cm long. a) Draw a picture and explain how based on this information you think these old TVs work. This does not have to be correct, it should just make sense (-: Feel free to invent a new old TV. b) Draw a free body diagram of the electrons in the electric field of the TV. (Be sure to indicate in your picture which plate is positive and which is negative.) c) How fast are the electrons in your TV based on the given information and the known mass and charge of electrons? d) What would be the acceleration of the electrons? e) Given the results of b), would you expect a TV to work lying on its back so that it had to shoot the electrons straight upwards against the force of gravity? Once you figure out what the physics question is the answer will (I hope) become apparent. Make sure you show a) a free body diagram of the electrons in the TV stand in a normal living room, and b) a free body diagram where the TV lays on the back. f) If you learned some new physics about your TV adjust your picture that you drew to start thinking about TVs.

Answer 1

A), B)

The voltage between the two plates are controlled to make the picture.

C)

velocity of the electron =

D)

acceleration of the electrons =

E) yes it wll work. The velocity and acceleration is too big to be influenced by gravity. The plates are not parralel to the path, the negetive source is working as the electron source and the +ve plate is the acceleration, situated perpendicularly to the electron path.

______________________________

a),b)