Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define magnetism and electromagnetism.
• Describe the properties of magnets and magnetic fields.
• Illustrate magnetic fields using field lines.
• Explain and calculate magnetic flux and flux density.
• Explain how an electric current produces a magnetic field.

Lesson summary

Magnetism and electromagnetism are fundamental concepts in electrical technology. They are the invisible forces that power many devices we use daily, from electric motors in appliances to the generators that supply electricity to our homes and industries. Understanding these concepts is crucial for any aspiring electrical technician or engineer. In South Africa, a reliable and skilled workforce in electrical technology is vital for maintaining and expanding our infrastructure, supporting industries, and improving the quality of life for all citizens.

Lesson notes

2.1 Magnetism: Magnetism is a force exerted by magnets when they attract or repel each other.

All magnets have two poles: a North pole and a South pole. Unlike poles attract each other (North attracts South), while like poles repel each other (North repels North, South repels South). 2.2 Magnetic Fields: A magnetic field is a region around a magnet where a magnetic force is exerted. We represent magnetic fields using magnetic field lines. These lines are imaginary lines that show the direction and strength of the magnetic field. Magnetic field lines always travel from the North pole to the South pole outside the magnet and from the South pole to the North pole inside the magnet, forming closed loops. The closer the magnetic field lines, the stronger the magnetic field. Magnetic field lines never cross each other. 2.3 Permanent Magnets vs.

Temporary Magnets: Permanent Magnets: These are materials that retain their magnetic properties for a long time (e.g., iron, nickel, cobalt, and certain alloys like alnico and ferrite).

Temporary Magnets: These materials become magnetized when placed in a strong magnetic field, but lose their magnetism when the field is removed (e.g., soft iron). 2.4 Electromagnetism: Electromagnetism is the interaction between electric currents and magnetic fields. A fundamental principle of electromagnetism is that a moving electric charge produces a magnetic field. This is the basis of electromagnets and many electrical devices. 2.5 Magnetic Field Around a Current-Carrying Conductor: When an electric current flows through a conductor (wire), it creates a magnetic field around the conductor. The shape and direction of the magnetic field depend on the shape and direction of the current.

For a straight conductor: The magnetic field lines form concentric circles around the conductor. The direction of the magnetic field can be determined using the right-hand rule: point your right thumb in the direction of the current, and your fingers will curl in the direction of the magnetic field. 2.6 Magnetic Flux (Φ): Magnetic flux is a measure of the total magnetic field that passes through a given area. It is represented by the symbol Φ (Greek letter Phi) and is measured in Weber (Wb). 2.7 Magnetic Flux Density (B): Magnetic flux density, also known as magnetic induction, is a measure of the strength of the magnetic field. It is defined as the magnetic flux per unit area. It is represented by the symbol B and is measured in Tesla (T). The relationship between magnetic flux density (B), magnetic flux (Φ), and area (A) is given by the formula: B = Φ / A Where: B is the magnetic flux density (in Tesla, T) Φ is the magnetic flux (in Weber, Wb) A is the area (in square meters, m²)