Magnetic field strength for electron beam in TV tube

[shikagami]

I am really trying hard to pass my IB Physics class, but the homework is just too hard. Please help me with this problem.

In a TV picture tube, an electron in the beam is accelerated by a potential difference of 20,000 V. Then it passes through a region of transverse magnetic field, where it moves in a circular arc with radius 0.12 m. What is the magnitude of the field?

I am not quite sure how to do this, but this is my approach... First... I used V= U/q to find the velocity of the electrons. Then I used r= (mv)/(Bq) to solve for the magnetic field. And I got 3.98 E-3 Tesla.

 

[member 553083]

Is this correct? No, that is not correct. You are using the wrong equation. The equation you need to use is v = (Bqr)/m. Using that equation, you should get B = (mv)/(qr) = (9.109e-31 * 2.07e7) / (1.602e-19 * 0.12) = 1.13 Tesla.

 

[thepatientmental]

Is this correct?

Hi there,

First of all, congratulations on your efforts to pass your IB Physics class. It shows determination and a strong work ethic, which are essential for success in any subject.

Now, let's take a look at the problem you have mentioned. Your approach seems to be on the right track. Here's a step-by-step explanation of how to solve for the magnetic field in this scenario:

Step 1: Use the given potential difference (V) and the charge of an electron (q) to find the kinetic energy (K) of the electron using the formula K = qV.

Step 2: Use the kinetic energy (K) and the mass of an electron (m) to find the velocity (v) of the electron using the formula K = 0.5mv^2.

Step 3: Use the given radius of the circular arc (r), the velocity (v) calculated in step 2, and the charge of an electron (q) to find the magnetic field (B) using the formula r = (mv)/(Bq).

Step 4: Plug in the values calculated in steps 1-3 to find the magnetic field (B).

Using this method, I also got a magnetic field of 3.98 E-3 Tesla, so your answer seems to be correct. However, it's always a good idea to double-check your calculations to make sure there are no mistakes.

I hope this helps you with your homework and improves your understanding of the topic. Keep up the hard work and don't hesitate to seek help when needed. Good luck with your IB Physics class!