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# Electric Current and Charge watch

1. 4). The electron beam in a TV tube travels 0.25m from the gun to the screen. The beam current is 4.0 mA. For Electrons travelling at 3.0 x 107 ms-1 (0.1 of the speed of light), calculate the number of electrons in a beam at any instant. The charge on one electron is 1.6 x 10-19 C.

I tried working out the time for the electrons to reach the screen using speed = distance/time. Then converting the current to Amps and then using Charge = Current x Time. Then dividing that charge by the charge on one electron which should hopefully give me the number of electrons in the beam, but it didn't =\ . What am I doing wrong?
2. 4). The electron beam in a TV tube travels 0.25m from the gun to the screen. The beam current is 4.0 mA. For Electrons travelling at 3.0 x 107 ms-1 (0.1 of the speed of light), calculate the number of electrons in a beam at any instant. The charge on one electron is 1.6 x 10-19 C.

I tried working out the time for the electrons to reach the screen using speed = distance/time. Then converting the current to Amps and then using Charge = Current x Time. Then dividing that charge by the charge on one electron which should hopefully give me the number of electrons in the beam, but it didn't =\ . What am I doing wrong?
Hey, looking at your working briefly (sorry gtg in a sec) I think it has to do with the fact that you've worked out how many electrons pass a given point in the time it takes for them to go from gun to screen, not how many there are in the beam. Think perhaps flux density or current density need to be considered. If I get any bright ideas i'll be back!
3. Maybe the Q=Ne formula comes into it?
4. Q=It See if you can work it out from there...
5. (Original post by ViralRiver)
4). The electron beam in a TV tube travels 0.25m from the gun to the screen. The beam current is 4.0 mA. For Electrons travelling at 3.0 x 107 ms-1 (0.1 of the speed of light), calculate the number of electrons in a beam at any instant. The charge on one electron is 1.6 x 10-19 C.

I tried working out the time for the electrons to reach the screen using speed = distance/time. Then converting the current to Amps and then using Charge = Current x Time. Then dividing that charge by the charge on one electron which should hopefully give me the number of electrons in the beam, but it didn't =\ . What am I doing wrong?

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