Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define electromagnetic induction and apply Faraday's Law.
• Explain the operation of generators and transformers.
• Solve problems involving power, voltage, and current.
• Calculate the efficiency of transformers.
• Describe factors affecting power loss in transmission lines.

Lesson summary

Electromagnetism is a fundamental force of nature that underpins many technologies we use daily. From the cellphones we use to communicate, to the appliances that make our lives easier, to the massive power grids that provide electricity to our homes and businesses, electromagnetism plays a crucial role. In the South African context, understanding electromagnetism is vital for addressing energy challenges, developing sustainable solutions, and participating in a technologically advanced economy. For example, many communities still lack reliable access to electricity.

Lesson notes

2.1 Electromagnetic Induction Electromagnetic induction is the process where a changing magnetic field induces an electromotive force (emf) – in other words, a voltage – in a conductor. This phenomenon is described by Faraday's Law of Electromagnetic Induction.

Faraday's Law: The induced emf in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit. Mathematically, Faraday's Law is expressed as: `ε = -N (ΔΦ / Δt)` Where: ε = induced emf (in volts, V) N = number of turns in the coil ΔΦ = change in magnetic flux (in webers, Wb) Δt = change in time (in seconds, s) Magnetic Flux (Φ): Magnetic flux is a measure of the amount of magnetic field lines passing through a given area.

It is given by: `Φ = BA cos θ` Where: B = magnetic field strength (in teslas, T) A = area of the loop (in square meters, m²) θ = angle between the magnetic field vector and the normal to the area The negative sign in Faraday's Law indicates the direction of the induced emf, as described by Lenz's Law.

Lenz's Law: The direction of the induced current is such that it opposes the change in magnetic flux that produced it. This essentially means that the induced current creates its own magnetic field that opposes the external magnetic field causing the induction.