1. Measurement of electron’s E/M.
We’re gonna present about the experiment of e/m.
e/m means the charge to mass ration of the electron.
나영일 , 김규태 , 곽진선 , 김승진 , 금종도 , 김민수

2. Table Purpose History Theory Apparatus Procedure Caution Control
Video Clip
Source
Here is the table of this presentation.
Measurement of electron’s E/M (2 Team)

3. Purpose To determine the charge to mass ratio of the electron.
The purpose of this experiment is to determine the charge to mass ratio of the electron.
Measurement of electron’s E/M (2 Team)

4. History Interactive animation J.J Thomson (1856~1940)
The history of this experiment started by the British physicist, Joseph John Thomson.
He researched the electric discharge of vaccum-tube and confirmed the particles of cathode ray.
Then he verified the existence of electron by determining e/m of the particles of cathode ray.
In 1897 J.J Thompson investigated the invisible cathode rays travelling through a glass bulb. He managed to change the direction of the rays using an electric field and concluded the rays had a negative electric charge. Charged particles are emitted by a hot filament at the rear of the evacuated tube and are accelerated by an applied potential difference V. There are deflecting plates which produce electric field at all points between them and coils of wire which generate magnetic field at right angle. The charges are affected by two forces-electrostatic force by the plate and magnetic force by the coil. If the electrostatic force and magnetic force acting on the charges are equal, the cathode rays reach without changing direction and appear the middle of the screen.
Interactive animation
Measurement of electron’s E/M (2 Team)

5. Theory(1) F = e v x B This is the theory of this experimentation.
The charge to mass ratio of an electron is measured using a set of Helmholtz coils and an electron beam tube.
When an electron (or any charged particle) moves through a magnetic field it experiences a force ("Lorentz force") given by
F = e u x B (1)
e = charge on an electron
v = velocity of the electron
B = magnetic flux density
Measurement of electron’s E/M (2 Team)

6. Theory(2) F=mv2/r F=evB mv2/r=evB
When a charge moves in the magnetic field with velocity v the charge get the magnetic force. The force is determined by the charge of the particle e its velocity v the strength of the magnetic field B. The magnetic force is given by F=evB Velocity and Magnetic field are perpendicular. The direction of the magnetic force and velocity is perpendicular. So the electrons makes an uniform circular motion. The centripetal force is given by F=mv2/r
Measurement of electron’s E/M (2 Team)

7. Theory(2-1) Circulating charge Motion of a charge
Measurement of electron’s E/M (2 Team)

8. Theory(3) mv2/2 = eV --- (3) mv2/r=evB e/m = 2V / (Br)2 ----- (4)
Charged particles are emitted by a hot filament and accelerated by potential difference V. and gain kinetic energy. So we can make equation
mv2/2 = eV
In this experiment the velocity of the electron is due to its being accelerated across a potential difference, V. The electron will then have kinetic energy
(3)
Solve Eq. (3) for u and substitute into Eq. (2) to obtain
e/m = 2V / (Br)2 (4)
Measurement of electron’s E/M (2 Team)

9. Apparatus(1) Helium filled tube Helmholtz coil
These are the apparatus we need for the experimentation.
We need helmholtz coils, e/m tube, power supply and cables.
This pictures shows helmholtz coils and e/m tube.
Measurement of electron’s E/M (2 Team)

10. Apparatus(2)
e/m tube
e/m tube is filled with helium at a pressure of 1/100mmHg, and contains electron gun and deflection plate.
Electron beams are visible because some of the electrons collide with helium atoms, which are excited and then radiate visible light.
Measurement of electron’s E/M (2 Team)

11. Apparatus(3) Helmholtz coils
Helmholtz coils are a pair of coils that are separated each other equal  to their radius of the coil. Each coils carries equal current in same direction.  It forms uniform magnetic field at the midpoint of coils. The magnitude of the magnetic field in the midpoint of coils is given by B=
Measurement of electron’s E/M (2 Team)

12. Apparatus(4) Power supplies & Multimeters
These are power supplies and multimeters to control the voltage and the current.
Measurement of electron’s E/M (2 Team)

13. Apparatus(5) The preparation is finished.
Measurement of electron’s E/M (2 Team)

14. Procedure(1) Here is the procedure of this experiment.
Turn the dials of the electric current and voltage to 0
Measurement of electron’s E/M (2 Team) 14

15. Procedure(2)
Connect the cables to the filament, Helmholtz coil and the electron accelerator(heater) from the power supply
Measurement of electron’s E/M (2 Team) 15

16. Procedure(3) Heat the filament of the tube about 2 to 3 minutes. 16
Measurement of electron’s E/M (2 Team) 16

17. Procedure(4) Switch on the heater voltage up to 150V slowly 17
Measurement of electron’s E/M (2 Team) 17

18. Procedure(5) Tune the current control dial to find I0(아이제로) 18
Measurement of electron’s E/M (2 Team) 18

19. Procedure(6)
Turn the current control dial to locate the electronic beam comes to scale 11 of the graduated straight line in e/m apparatus.
Then measure the electric current and find the radius of the electronic beam.
Measurement of electron’s E/M (2 Team) 19

20. Procedure(7)
With same method make the end of electron beam goes to 10,9,8,7, and measure the electric current I’ and the radius of electron beam.
Measurement of electron’s E/M (2 Team) 20

21. Caution
Before the experimentation, heat up the filament adequately. (about 2 to 3 minutes)
Confirm the electric current and the voltage are both to be set at 0 before the work.
Increase the voltage slowly during the experimentation.
Make sure that the electric current should not be over 1.5A.
The radius of the action should be measured accurately, when you measure the locus of the electron beam.
Before the experiment, you should notice this article.
Measurement of electron’s E/M (2 Team)

22. After the Exp.
1. Decrease the Heater voltage to 0V and turn off the power.
2. Decrease the voltage of the filament and Turn off power.
3. Turn off the Helmholtz coils.
Decrease the Heater voltage to 0V and turn off the power.
2. Decrease the voltage of the filament and Turn off power.
3. Turn off the Helmholtz coils.
Measurement of electron’s E/M (2 Team)

23. Video clip This video file shows how to experiment.
Measurement of electron’s E/M (2 Team)

24. Source http://newton.hanyang.ac.kr/ http://higheredbcs.wiley.com/
These are the sources of this presentation.
Please ask to us anytime about this experiment.
Thank you for listening the presentation.
Measurement of electron’s E/M (2 Team)