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Give me some tips for this test related to electric fields and circuits

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Homework Statement



I'm currently doing Physics 12.

Its about electric fields, voltage, current, power, gravitation field and series, parallel and series-parallel circuits.

I've already taken the test once and got 48% because I didn't fully study the last section which involved series-parallel circuits.

Anyway its a total of 70 marks

34 marks Multiple choice (I got them all correct)
14 marks Series-parallel circuits calculations of voltage, current, resistance (I got none right)
22 marks about a cathode ray tube and deflection (I got none right)

So as you can see it seems like the last section of the course was the most important one.

The Attempt at a Solution



The multiple choice was completely understand and all correct. When I got to the series-parallel circuit questions I didn't know what to do because I didn't study that section yet and so lost 14 marks for nothing.

Next is the last part of the test worth 22 marks which I flunked completely and need your advice about:

A cathode ray tube with a voltage Va shoots itself in between two metal plates. The voltage between the plates is Vb. In front of the two metal plates is a screen. Its asking about deflection.

First there was a graph of Voltage versus deflection graph. Voltage on y-axis and deflection on x-axis

1.) Find the slope of the line. I didn't know where to start.
2.) What is the relationship between voltage and deflection?
3.) What is the deflection on the screen?

Those are the only questions I can remember but there is a lot more and I worded them to my memory.

Can anyone give any advice or references to a voltage versus deflection graph? It was Va and D.
 

Answers and Replies

  • #2
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Relationship between accelerating voltage and distance in cathode ray tube?

I really need help.

I'm going to re-take a test that involves questions about a Cathode Ray Tube that shoots electrons in between two deflecting plates that have a flourescent screen at the end of them.

First it shows me a diagram and then a graph of Va on the y-axis and D on the x-axis.

Va means the accelerating voltage at the cathode ray tube and D means distance. (I don't remember if D was distance or deflection)

In this graph they asked me to find the slope of the line.

Then to find the line equation y = mx+b

Then they asked the relationship between Va and d and then asked about several other things thtat I don't remember that were on the test.

How would I do any of this? Where could I start.

How do I find the slope and the line equation of such a graph?

This is Physics 12.
 
  • #3
berkeman
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I really need help.

I'm going to re-take a test that involves questions about a Cathode Ray Tube that shoots electrons in between two deflecting plates that have a flourescent screen at the end of them.

First it shows me a diagram and then a graph of Va on the y-axis and D on the x-axis.

Va means the accelerating voltage at the cathode ray tube and D means distance. (I don't remember if D was distance or deflection)

In this graph they asked me to find the slope of the line.

Then to find the line equation y = mx+b

Then they asked the relationship between Va and d and then asked about several other things thtat I don't remember that were on the test.

How would I do any of this? Where could I start.

How do I find the slope and the line equation of such a graph?

This is Physics 12.
Accelerating plates and deflection plates are two different things. The accelerating plates (in simple terms) are the cathode where the electrons are emitted, and the anode, which is the front plate of the CRT where the phosphur goes.

The deflection plates would be plates that are horizontal or vertical, just after the electron gun portion (where the cathode is). The electric field between the two horizontal deflection plates can be used to deflect the electron beam vertically, and the E-field between the two vertical deflection plates can be used to deflect the electron beam horizontally.

Based on the question asking for a graph of something versus the electric field somewhere, I'd guess they are asking for the deflection as a function of the deflection plate voltage, for some fixed acceleration plate voltage. Or the other way around maybe.

It would be best if you could find the exact wording of the question, or else work problems in your textbook that are similar.

CRTs can also use magnetic fields from horizontal and vertical deflection coils to steer the electron beam. You might also end up with some questions like that on future problem sets or exams.
 
  • #4
berkeman
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7,291
(Two threads with similar questions merged)
 

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