An electron is accelerated from rest by a potential...

An electron is accelerated from rest by a potential difference of 450 V. It then enters a uniform magnetic field of magnitude 280 mT with its velocity perpendicular to the field. Calculate the speed of the electron. Calculate the radius of its path in the magnetic field.

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Transcript

00:01 All right, so a couple steps to this one.

00:02 We have an electron accelerated over a voltage, and then it enters a magnetic field.

00:08 We want to get the speed of the electron just before it enters that magnetic field.

00:13 And then we want to know the radius at which it rotates, because if its speed is perpendicular to the magnetic field, it's going to turn in a circular motion.

00:23 So we're going to need a few things.

00:24 We need the mass of the electron.

00:26 That's 9 .11 times 10 to the minus 31 kilograms.

00:31 Okay.

00:32 We're going to need the charge of the electron at some point two.

00:35 That's 1 .6 times 10 to the minus 19 couloms.

00:40 And we'll use the equation, so we'll show them up as we use them.

00:44 So we're told that it's accelerated across 450 volts.

00:48 Volt is the same as joules per coulomb.

00:50 So 450 volts times the charge of an electron, 1 .6 times 10 of the minus 19 couloms.

00:57 That's going to give us our kinetic energy.

00:59 And of course, kinetic energy is one half mv squared.