# Viva Questions:

## e/m (charge to mass) ratio of the electron is determined using the cathode ray tube in this experiment

1Q. What Is Cathode Ray Tube (CRT)?

2Q. What is electron gun in CRT?

3Q. Why do we use filament in CRT?

4Q. How electrons emit from the cathode?

5Q. How do you accelerate electrons in CRT?

6Q. What is the role of cathode and anode in CRT in reference to the emission of electrons?

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## Questions related to the Deflecting Section of CRT

7Q. How deflecting plates affect the path of electron beams?

8Q. Does electron beam deflects by the electrodes only?

9Q. What is the formula for force on a charged particle in the presence of the electric field?

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10Q. What is the formula for force on charged particles in the presence of the Magnetic field?

11Q. In the presence of a uniform magnetic field when the electron beam enters into the field perpendicularly, what type of path electron beam will follow?

12Q. How centripetal force contribute in the question 11?

13Q. How to determine one the radius r in the centripetal force formula, what is a concept?

14Q.Does forward or reverse biasing can affect the path of the electron beam?

## The screen of Cathode Ray Tube

15Q. What type of material produces the light on the screen of CRT when electrons strike?

16Q. Does magnetic coil is already built in Cathode Ray Tube?

or

Does magnetic field source is inbuilt in CRT to produce the magnetic field or we use it from externally?

17Q. Suppose you deflected the electron beam on screen by some distance, can you bring at original position by the external electric or magnetic field at the original position?

18Q. In reference to 17 th question which field is more suitable to handle this problem, electric or magnetic and why?

19Q.  What is the standard value of charge to mass ratio of the electron in JJ Thomson method?

20Q. What formula you have used to determine the charge to mass ratio of the electron and what is the origin of it?

## Magnetic Field Determination

21Q. Are you using Helmholtz’s Coils or permanent bar magnets in this experiment to balance the electric force on the electron?

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22Q. If you are using Helmholtz’s Coils how you will determine the magnetic field, what is the formula used for it?

23Q. If you are using a bar magnet then how?

24Q. Does earth’s magnetic field depend on the latitude and altitude?

25Q. How do you will calculate the earth’s magnetic field at your place?

26Q. Does the magnetic compass in the mobile phone can tell the approximate value of the earth’s magnetic field?

27Q. What are the unit and approximate value of the earth’s magnetic field?

These are some basic viva questions, which one should know to determine the value of charge to mass ratio of the electron in J J Thomson’s experiment. If you don’t have the answer to any question you can ask for help to me. Also, if you have information related to these questions it means you know almost everything about the experiment.