5.0 Electronic
5.1 Electron
Preparation before class (Pre-class task). (Watch the video and make some notes).
Summary of the topic.
5.1.1 Describe the thermionic emission and cathode ray.
Watch the video starting at minute 2:01.
Make some notes. Answer the quiz.
5.1.2 Describe the effect of cathode ray in the electric field and magnetic field.
- Cathode rays are negatively charged because they are produced by negative electrode (cathode).
- The rays will be deflected towards a positive plate in an electric field.
- Deflected by magnetic fields and electric fields.
- The direction of deflection can be determined based on the Fleming's left-hand rule.
5.1.3 Determine the speed of electron in the cathode ray tube.
There is energy conversion of electrons in cathode rays.
1) At the cathode; Electrical energy ➝ heat energy
2) At the electron gun; Electrical potential energy ➝ Kinetic energy
Hence, based on the principle of convervation of energy,
electrical potential energy = kinetic energy
eV = 1/2 mv^2
where
e = charge of electron = 1.6 X 10^19 C
V= potential difference
m= mass of an electron = 9.1 X 10^-31 kg
v= maximum velocity of electron
Thus, we can obtain the speed of electron using the formula. Rearrange the formula, and walla!