Cathode ray tubes in old television sets worked by accelerating electrons and then deflecting them with magnetic fields onto a p
hosphor screen. The magnetic fields were created by coils of wire on either side of the tube carrying large currents. In one such TV set, the phosphor screen is 51.2 cm wide, and is 11.1 cm away from the center of the magnetic deflection coils (that is, the center of the region of magnetic field). The electron beam is first accelerated through a 22,000 V potential difference before it enters the magnetic field region, which is 1.00 cm wide. The field is approximately uniform and perpendicular to the velocity of the electrons. If the field were turned off, the electrons would hit the center of the screen. What magnitude of magnetic field (in mT) is needed to deflect the electrons so that they hit the far edge of the screen
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Hey JayDilla, I get 1/3. Here's how:
Kinetic energy due to linear motion is:
where
giving
The rotational part requires the moment of inertia of a solid cylinder
Then the rotational kinetic energy is
Adding the two types of energy and factoring out common terms gives
Here the "1" in the parenthesis is due to linear motion and the "1/2" is due to the rotational part. Since this gives a total of 3/2 altogether, and the rotational part is due to a third of this (1/2), I say it's 1/3.
Kinetic energy due to linear motion is:
where
giving
The rotational part requires the moment of inertia of a solid cylinder
Then the rotational kinetic energy is
Adding the two types of energy and factoring out common terms gives
Here the "1" in the parenthesis is due to linear motion and the "1/2" is due to the rotational part. Since this gives a total of 3/2 altogether, and the rotational part is due to a third of this (1/2), I say it's 1/3.