, ichael Faraday, James Clerk Maxwell, Nikola Tesla, Hans Christian
M Oersted and Heinrich Lenz to mention but a few of scientists who have
since passed on and who have contributed to scientific developments that
continue to make our civilization better. These are the names of top
physicists and pioneers in the field of electromagnetism or
electrodynamics. Now, two centuries after their departure, the importance
of their discoveries is very clear and cannot be overemphasized. From the generation
of electrical power to the storage of information in a computer hard disk drive and from
the design and functioning of a loud speaker to the transmission of information over
TV and radio, their discoveries and applications thereof live on. This topic aims to
discuss the applications of the theories that underpin electromagnetism in electrical
machines such as generators and motors. It also goes a step further to discuss two
types of current i.e. direct current as well as alternating current. Lastly, this paper also
brings forth to the attention of the learner, the various types of exam-type questions
related to this topic in grade 12.
Chapter Outline
1. Electrical machines i.e. generators and motors.
2. Alternating current.
Chapter goals.
By the end of this chapter, you should be able to:
1. State the energy conversion that occurs in generators.
2. Use the principle of electromagnetic induction (Faraday’s law) to explain how a
generator works.
3. Explain the functions of the components of an AC and a DC generator using
words and pictures.
4. Use words and pictures to explain how a DC generator works and how it differs
from an AC generator.
5. Explain why a current-carrying conductor placed in a magnetic field will turn by
referring to the force exerted on moving charges by a magnetic field and the
torque on the coil.
1
© O.F. MAHLOMBE, 2015. Download notes from onedrive: http://1drv.ms/1gYCyQO
,6. Use words and pictures to explain the basic principle of an electric motor.
7. State the energy conversion that occurs in motors.
8. Use the motor effect to explain how a motor works.
9. Explain the functions of the components of a motor.
10. State examples of the use of motors and generators.
11. State the advantages of alternating current over direct current.
12. Sketch graphs of voltage versus time and current versus time for an AC circuit.
13. Define the term rms for an alternating voltage or an alternating current.
𝐼𝑚𝑎𝑥 𝑉𝑚𝑎𝑥
14. Solve problems using 𝐼𝑟𝑚𝑠 = and 𝑉𝑟𝑚𝑠 =
√2 √2
1
15. Solve problems using 𝑃𝑎𝑣𝑒 = 𝐼𝑟𝑚𝑠 𝑉𝑟𝑚𝑠 , 𝑃𝑎𝑣𝑒 = 𝐼𝑚𝑎𝑥 𝑉𝑚𝑎𝑥 (for a purely resistive
2
2
𝑉𝑟𝑚𝑠
circuit), 𝑃𝑎𝑣𝑒 = 𝐼𝑟𝑚𝑠 2 𝑅 and 𝑃𝑎𝑣𝑒 = 𝑅
2
© O.F. MAHLOMBE, 2015. Download notes from onedrive: http://1drv.ms/1gYCyQO
, 1. Electrical machines (Generators and motors)
In electrodynamics, a generator is a device that converts input mechanical energy from
an external source into electrical energy as output.
The following figure shows a picture of a generator.
Figure 1: A picture of a generator
Energy conversion in generators (EXAMINABLE)
A generator converts mechanical energy into electrical energy.
The mechanical energy can come from any mechanism that rotates the rotor or the
arm of the generator. When the turbine (attached to the rotor of the generator) turns
(a mechanical process), through principles such as what will be explained later, emf
(electrical energy) is induced in the terminals of the generator.
Coal-fired power stations
Figure 2: Picture that represents how electricity is generated at a coal-fired power plant.
(NOT FOR EXAM PURPOSES)
3
© O.F. MAHLOMBE, 2015. Download notes from onedrive: http://1drv.ms/1gYCyQO
M Oersted and Heinrich Lenz to mention but a few of scientists who have
since passed on and who have contributed to scientific developments that
continue to make our civilization better. These are the names of top
physicists and pioneers in the field of electromagnetism or
electrodynamics. Now, two centuries after their departure, the importance
of their discoveries is very clear and cannot be overemphasized. From the generation
of electrical power to the storage of information in a computer hard disk drive and from
the design and functioning of a loud speaker to the transmission of information over
TV and radio, their discoveries and applications thereof live on. This topic aims to
discuss the applications of the theories that underpin electromagnetism in electrical
machines such as generators and motors. It also goes a step further to discuss two
types of current i.e. direct current as well as alternating current. Lastly, this paper also
brings forth to the attention of the learner, the various types of exam-type questions
related to this topic in grade 12.
Chapter Outline
1. Electrical machines i.e. generators and motors.
2. Alternating current.
Chapter goals.
By the end of this chapter, you should be able to:
1. State the energy conversion that occurs in generators.
2. Use the principle of electromagnetic induction (Faraday’s law) to explain how a
generator works.
3. Explain the functions of the components of an AC and a DC generator using
words and pictures.
4. Use words and pictures to explain how a DC generator works and how it differs
from an AC generator.
5. Explain why a current-carrying conductor placed in a magnetic field will turn by
referring to the force exerted on moving charges by a magnetic field and the
torque on the coil.
1
© O.F. MAHLOMBE, 2015. Download notes from onedrive: http://1drv.ms/1gYCyQO
,6. Use words and pictures to explain the basic principle of an electric motor.
7. State the energy conversion that occurs in motors.
8. Use the motor effect to explain how a motor works.
9. Explain the functions of the components of a motor.
10. State examples of the use of motors and generators.
11. State the advantages of alternating current over direct current.
12. Sketch graphs of voltage versus time and current versus time for an AC circuit.
13. Define the term rms for an alternating voltage or an alternating current.
𝐼𝑚𝑎𝑥 𝑉𝑚𝑎𝑥
14. Solve problems using 𝐼𝑟𝑚𝑠 = and 𝑉𝑟𝑚𝑠 =
√2 √2
1
15. Solve problems using 𝑃𝑎𝑣𝑒 = 𝐼𝑟𝑚𝑠 𝑉𝑟𝑚𝑠 , 𝑃𝑎𝑣𝑒 = 𝐼𝑚𝑎𝑥 𝑉𝑚𝑎𝑥 (for a purely resistive
2
2
𝑉𝑟𝑚𝑠
circuit), 𝑃𝑎𝑣𝑒 = 𝐼𝑟𝑚𝑠 2 𝑅 and 𝑃𝑎𝑣𝑒 = 𝑅
2
© O.F. MAHLOMBE, 2015. Download notes from onedrive: http://1drv.ms/1gYCyQO
, 1. Electrical machines (Generators and motors)
In electrodynamics, a generator is a device that converts input mechanical energy from
an external source into electrical energy as output.
The following figure shows a picture of a generator.
Figure 1: A picture of a generator
Energy conversion in generators (EXAMINABLE)
A generator converts mechanical energy into electrical energy.
The mechanical energy can come from any mechanism that rotates the rotor or the
arm of the generator. When the turbine (attached to the rotor of the generator) turns
(a mechanical process), through principles such as what will be explained later, emf
(electrical energy) is induced in the terminals of the generator.
Coal-fired power stations
Figure 2: Picture that represents how electricity is generated at a coal-fired power plant.
(NOT FOR EXAM PURPOSES)
3
© O.F. MAHLOMBE, 2015. Download notes from onedrive: http://1drv.ms/1gYCyQO
