Saturday, March 28, 2009


  1. Doping is a process of adding a certain amount of specific impurities to semiconductors to increase their conductivity
  2. Two types of doping:
  • p-type semiconductors
  • n-type semiconductors
p-type semiconductors

1. Si (pure/ intrinsic semiconductor) have valency of 4
2. Al (impurity) have four e valens
3. When Al is added to Si, there will be one less e - p-type semiconductor is produced
4. No. of e > No. of holes

n-type semiconductors
1. Si (pure/ intrinsic semiconductor) have valency of 4
2. P (impurity) have three e valens
3. When P is added to Si, there will be one extra e - n-type semiconductor is produced
4. No. of holes > No. of e

Tuesday, March 24, 2009

Diode Semiconductor

9.2 Understanding Diode Semiconductor

Solids: Conductor VS Semiconductor VS Insulator
  1. Conductor: Have free electrons that can drift between their atoms
  2. Semiconductor: Have electrons and holes
  3. Insulator: Don't have free electron
Additional information: Energy bands for solids
The conductivity of semiconductors also can be increased by
  • rising the temperature
  • shining light on it
  • adding impurities to it (doping)


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Monday, March 23, 2009


Application of CRO
1. Display the wave forms of voltage
2. Measuring the potential difference (a.c & d.c)

3. Measure a short time of duration/ interval


The Cathode Ray Oscilloscope (CRO)

Three parts of the CRO:
1. Electron gun
  • Filament: Is heated when current flows through it. It is used to heat up the cathode.
  • Cathode: Heated cathode emits electrons through the process of thermionic emissions.
  • Control grid: Control the number of electrons in the electron beams.
    The more negative the grid, the fewer the electrons are emitted from the electron gun and the less the brightness of the bright spot on the screen.
  • Focusing anode: To focus the electrons into a beam and to attract electrons from the area of the control grid.
  • Accelerating anode: To accelerate the electron beam towards the screen.

2. Deflection system
  • The deflection system allows the electron beam to be deflected from its straight-line path when it leaves the electron gun.
  • Y-plates is to move the electron beam vertically up and down the screen when an input voltage is applied across it.
3. Fluorescent screen

Application of CRO
  1. Measuring potential difference
  2. Measuring short intervals
  3. Displaying wave forms

Friday, March 13, 2009


9.1 Understanding the uses of the Cathode Ray Oscilloscope
Properties of cathode rays

Friday, March 6, 2009


9.1 Understanding the uses of the Cathode Ray Oscilloscope
Thermionic emission
Factors affecting the rate of thermionic emission
  1. Surface area of metal - Directly proportional
  2. Temperature of metal - Directly proportional
  3. Types of metal - Depends of the metal type
  4. Nature of metal surface - Will increase the acceleration of the electrons
Cathode rays
  1. Thermionic emissions can be used to produce a continuous flow of electrons in a cathode ray tube.
  2. The beam of electrons moving from cathode to anode is called cathode ray.

Thursday, March 5, 2009


9.1 Understanding the uses of the Cathode Ray Oscilloscope
Thermionic emission
1. A metal surface has many free electrons
2. When it is heated to certain temperature, some of the electrons have gained enough kinetic energy to break free and escape to surroundings.
3. This effect is known as thermionic emission.

Tuesday, March 3, 2009

March Test 2009

Friday/ 6.50 - 8.20 a.m

Form 5: Paper 3 (4531/3)
Form 4:
  1. 4S/ P/ C - Ch. 1 - Ch. 2 (2.4)
  2. 4I - Paper 3 (4531/3/ Section A)
Be READY !!!