Month: March 2014

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. 

4 Sources of Energy Used to Generate Electricity – Hydroelectric

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

  1. It is renewable energy.
  2. Building a dam does not pollute the environment.
  3. In a lot of countries, water can be easily obtained and is free.
  4. Building a hydroelectric plant does not involve very high technology as a nuclear power plant.

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

  1. Building a dam will cause a large area flooded with water, and hence seriously destroys the ecosystem nearby.
  2. The flooded area causes the loss of wildlife habitat and agriculture land.
  3. Dam failure happens will cause a disaster to the lower reaches area of the river.
  4. The cost to build a dam is very high.

4 Uses of Electromagnet – Circuit Breaker

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  1. The figure above shows the structure of a circuit breaker.
  2. A circuit breaker is an automatic switch that cut off current in a circuit when the current becomes too large.
  3. When the current in a circuit increases, the strength of the electromagnet will increase in accordance; this will pull the soft iron armature towards the electromagnet.
  4. As a result, the spring pulls apart the contact and disconnects the circuit immediately, and the current stop to flow.
  5. We can reconnect the circuit by using the reset button. The reset button can be pushed to bring the contact back to its original position to reconnect the circuit.

4 Law of Electromagnetic Induction

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There are 2 principal laws of electromagnetic induction:

  1. Faraday’s law
  2. Lenz’s law

Faraday’s Law

  1. The magnitude of the induced e.m.f is determined by Faraday’s Law.
  2. Faraday’s Law states that the magnitude of the induced e.m.f is directly proportional to the rate of change of magnetic flux through a coil or alternatively the rate of the magnetic flux being cut.
  3. Therefore, the induced emf can be increased by
    1. using a stronger magnet
    2. increase the speed of the relative motion
    3. increase the number of turns of the coil

Lenz’s Law

  1. When a magnet is moved into and out of a coil, the induced current that flows through the coil can be determined from Lenz’s Law.
  2. Lenz’s Law states that the induced current always flows in the direction that opposes the change in magnetic flux.
  3. Lenz’s Law obeys the principle of conservation of energy. Work is done to move the magnet against the repulsive force. This work done is converted to electric energy which manifests as an induced current.
  4. For a conductor in a closed circuit moving perpendicular to a magnetic field and hence cutting its magnetic flux, the direction of the induced current is determined from Fleming’s Right-Hand Rule.
  5. Fleming’s Right-Hand Rule is used to determine the direction of the induced current that flows from the wire when there is relative motion with respect to the magnetic field

Physics Animation
Applet
Lenz’s Law – Molecular Expression

Kinetic Energy

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Kinetic Energy
Kinetic energy is the energy of motion.

Equation of Kinetic Energy

Example
Determine the kinetic energy of a 2000-kg bus that is moving with a speed of 35.0 m/s.

Answer:

Kinetic Energy,

4.1 Force on a Current Carrying Conductor in a Magnetic Field

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  1. We have learned that when current flows in a conductor, a magnetic field will be generated.
  2. When the current-carrying conductor is placed in a magnetic field, the interaction between the two magnetic fields will produce a resultant field known as the catapult field as shown in the figure below.
  1. The catapult field is a non-uniform field where the field at one side is stronger than the other side.
  2. As a result, a force is produced to move the current-carrying conductor from the stronger field to the weaker field.
  3. The force produced by a catapult field is called the catapult force.
  4. The direction of the force can be determined by Fleming’s left-hand rule as shown in Figure below.
  1. The forefinger, middle finger and the thumb are perpendicular to each other. The forefinger points along the direction of the magnetic field, middle finger points in the current direction and the thumb points along the direction of the force.
  2. The strength of the force can be increased by:
    1. Increase the current
    2. Using a stronger magnet
    3. using a longer wire
    4. arranging the wire perpendicular to the direction of the magnetic field.

Recommended Videos

Force on a current-carrying conductor in a magnetic field – Physics

External Resources

Physics Animation

Lorentz Force

External Link

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4 Uses of Electromagnet – Telephone Earpiece

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  1. An electromagnet is used in the earpiece of a telephone. The figure shows the simple structure of a telephone earpiece.
  2. When you speak to a friend through the telephone, your sound will be converted into electric current by the mouthpiece of the telephone.
  3. The current produced is a varying current and the frequency of the current will be the same as the frequency of your sound.
  4. The current will be sent to the earpiece of the telephone from your friend.
  5. When the current passes through the solenoid, the iron core is magnetised. The strength of the magnetic field changes according to the varying current.
  6. When the current is high, the magnetic field will become stronger and when the current is low, the magnetic field becomes weaker.
  7. The soft-iron diaphragm is pulled by the electromagnet and vibrates at the frequency of the varying current. The air around the diaphragm is stretched and compressed and produces sound wave.
  8. The frequency of the sound produced in the telephone earpiece will be the same as your sound.

4 Uses of Electromagnet – Electromagnetic Relay

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  1. A relay is an electrical switch that opens and closes under the control of another electrical circuit.
  2. The switch is operated by an electromagnet to open or close one or many sets of contacts.
  3. A relay has at least two circuits. One circuit can be used to control another circuit. The 1st circuit (input circuit) supplies current to the electromagnet.
  4. When the switch is close, the electromagnet is magnetised and attracts one end of the iron armature.
  5. The armature then closes the contacts (2nd switch) and allows current flows in the second circuit.
  6. When the 1st switch is open again, the current to the electromagnet is cut, the electromagnet loses its magnetism and the 2nd switch is opened. Thus current stop to flow in the 2nd circuit.

4 Uses of Electromagnet – Electric Bell

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  1. When the switch is on, the circuit is completed and current flows.
  2. The electromagnet becomes magnetised and hence attracts the soft-iron armature and at the same time pull the hammer to strike the gong. This enables the hammer to strike the gong.
  3. As soon as the hammer moves towards the gong, the circuit is broken. The current stops flowing and the electromagnet loses its magnetism. This causes the spring to pull back the armature and reconnect the circuit again.
  4. When the circuit is connected, the electromagnet regains its magnetism and pull the armature and hence the hammer to strike the gong again.
  5. This cycle repeats and the bell rings continuously.

Physics Animation
Applet
Simple Buzzer

Youtube Video