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5.1 Thermionic Emission

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Thermionic Emission

  1. Thermionic emission is a process of emission of charged particles (known as thermion) from the surface of heated metal.
  2. The charge particles normally are electrons.
  3. The rate of emission (number of electrons emitted in 1 second) is affected by 4 factors, namely
    1. the temperature of the heated metal,
      When the temperature of the metal increase, the emission rate of electrons will increase.
    2. the surface area of the heated metal,
      When the surface area of the metal increase, the emission rate of electrons will increase.
    3. the types of metal
      The rates of thermionic emission are different with regard to different types of metals.
    4. the coated material on the surface of the metal.
      If the surface is coated by a layer of barium oxide or strontium oxide, the rate of emission will become higher.

Thermionic Diode

  1. Thermionic emission is applied in a thermionic diode.
  2. A diode is an electrical component that only allowed current flows in one direction.
  3. The figure below shows the illustration of a thermionic diode.
  4. Electrons can only be released from the tungsten filament (when it is hot) and move toward the anode which is connected to the positive terminal.
  5. Electrons are not allowed to move in the opposite direction because no electrons will be released from the anode.
  6. As such, the electrons can only move from left to right but not the other way round.

5 Cathode Ray Oscilloscope

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Cathode Ray Oscilloscope

(Cathode Ray Tube Television)
  1. Cathode-ray tubes have become part of everyday life.
  2. They can be found in the screens of television sets and computer monitors.
  3. In the Physics laboratory, we use the cathode-ray tube in the oscilloscope to study waveforms.
  4. In SPM, you need to know
    1. How cathode ray is produced (Thermionic emission and electron gun)
    2. The characteristics of cathode ray (Study by using the Maltese Cross Tube and Deflection Tube).
    3. the structure of a Cathode Ray Oscilloscope
    4. how to operate a Cathode Ray Oscilloscope
    5. the uses of a Cathode Ray Oscilloscope
(Cathode Ray Oscilloscope)

5 SPM Form 5 Physics Chapter 4 – Electronic

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  1. Cathode Ray Oscilloscope
    1. Thermionic Emission
    2. Cathode Ray
    3. Structure of Cathode Ray Oscilloscope
    4. Using Cathode Ray Oscilloscope
    5. Uses of Cathode Ray Oscilloscope
      1. Measuring Potential Difference
      2. Measuring Short Time Interval
      3. Displaying Wave Forms
  2. Semiconductor
    1. Holes and Free Electrons
    2. Flows of Free Electrons and Holes
    3. Doping a semiconductor
    4. N-Type Semiconductor
    5. P-Type Semiconductor
    6. Summary
  3. Semiconductor Diodes
    1. Forward Bias and Reverse Bias
    2. Diodes as Rectifiers
    3. Full Wave Rectification
    4. Capacitor Smoothing
  4. Transistors
    1. Connection of Transistors
    2. Current in Transistor
    3. Uses of Transistor
      1. Current Amplifier
      2. Automatic Switch
  5. Logic Gates
    1. Symbol, Boolean Algebra and Truth Table
    2. Combination of Logic Gate
    3. NAND gate as the universal gate

    Objective Questions

    1. Thermionic Emission and Cathode Ray (5 Questions)
    2. Cathode Ray Oscilloscope (5 Questions)
    3. Semiconductor (5 Questions)
    4. Semiconductor Diode (6 Questions)
    5. Transistors (7 Questions)
    6. Logic Gates (5 Questions)

4 SPM Form 5 Physics Mind Map Formulae List – Chapter 3

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Click on the image to enlarge.

The image above shows the formulae that students need to know in Malaysia SPM Physics syllabus in Mind Map form. You may click on the image to enlarge it for a better view. You may also download and print it out for further reference.

Electromagnetism if the third chapter in SPM Form 5 Physics. Not many calculation in this chapter. Most of the calculation questions are related to transformer. Questions related to the root mean square voltage and current rarely come out in exam.

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4 Transmission of Electricity

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Q: Why the voltage is stepped up before transmitting electricity over a long distance?

A: Stepping up the voltage can reduce the current in the cable. This reduces the power loss in the cable during transmission.

[This image is shared by its author Aatu Liimatta in Wikipedia Image. This file is licensed under the Creative Commons Attribution ShareAlike 2.5 License.]

Problems Involving Electricity Transmission.

  1. Power Loss During Transmission.
  2. The high voltage transmission cable is very dangerous.
  3. The cost of the cables is high.
  4. Charge leakage may happen between cables and earth.
  5. Pylons may be struck by lightning.
  6. Pylons and cables may be struck by light aircraft.

     

    4 Sources of Energy Used to Generate Electricity – Wind Energy

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    Wind Power[This image is shared by Wagner Christian. This file is licensed under the Creative Commons Attribution ShareAlike 2.5 License. ]

    Advantages

    The advantages of using wind as a source of energy to generate electricity are.

    1. It is renewable energy.
    2. It does not pollute the environment.
    3. It is suitable for the mountain area because the wind speed in the mountain area is relatively high.

    Disadvantages

    The disadvantages of using wind as a source of energy are.

    1. A large area is needed to build the windmills.
    2. The windmills will produce a high level of noise.
    3. The power generated is inconsistent due to the inconsistent of the wind speed and wind direction.

    4 Sources of Energy Used to Generate Electricity – Biomass

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    1. Biomass is biological material derived from living organisms such as wood and animal waste.
    2. As a renewable energy source, biomass can either be used directly via combustion to produce heat or indirectly after converting it to various forms of biofuel.
    3. Heat energy produced from the burning of biomass can be used to generate electricity.

    Advantages

    1. It is renewable energy.
    2. Using biomass to generate electricity can reduce the disposal of organic waste.
    3. Liquid biofuels will not pollute the air because they are lead-free and sulphur-free.

    Disadvantages

    1. Large storage space is required to store the biomass.
    2. Land utilization can be considerable. Can lead to deforestation.
    3. The overall process can be expensive

    4 Sources of Energy Used to Generate Electricity – Nuclear Power

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    Nuclear Power

    Advantages

    The advantages of using nuclear energy as a source of energy to generate electricity are.

    1. The nuclear fuel such as uranium and plutonium has high energy capacity. A small amount of uranium can produce a huge amount of energy.
    2. Nuclear energy does not pollute the air.

    Disadvantages

    The disadvantages of using nuclear energy as a source of energy are.

    1. Hazardous radioactive waste is produced during a nuclear reaction.
    2. The radioactive waste will cause pollution in a very large area if leakage happens in the nuclear power plan.
    3. The cost to maintain a nuclear plant is very high.
    4. Building a nuclear plant involving very high technology. Only a few countries own such technology. 

    4 Sources of Energy Used to Generate Electricity – Solar Energy

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    Solar power

    Advantages

    The advantages of using solar energy as a source of energy to generate electricity are.

    1. It is renewable energy.
    2. Sunlight is free and can be obtained easily.
    3. It does not pollute the air.

    Disadvantages

    The disadvantages of using solar energy as a source of energy are.

    1. A large area is needed to install the solar plate.
    2. The amount of sunlight at the non-tropical area depends on the season.
    3. The energy collected need to be stored in a cell so that it can be used at the time sunlight is not present.
    4. Its capacity is limited by the capacity of the cell. Normally a cell has relatively low capacity.

    4 Sources of Energy Used to Generate Electricity – Fossil Fuel

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    Fossil Fuel.

    Advantages

    The advantages of using fossil fuel such as petroleum, natural gas and coal as a source of energy to generate electricity are.

    1. It is relatively easy to be collected as they are present in large amount in one place.
    2. It contains high energy capacity.

    Disadvantages

    The disadvantages of using fossil fuel as a source of energy are.

    1. It releases a lot of carbon dioxide when it is burned. A large amount of carbon dioxide present in the atmosphere will cause an increase in the temperature of the atmosphere, known as global warming. Global warming is the most serious environmental problem that we are facing now.
    2. Fossil fuels are non-renewable energy.
    3. Pollute the air. Burning of fossil fuel will release particles and some hazardous gases such as sulphur dioxide and nitrogen dioxide which will pollute the air.