Electromagnetism · SHS2 Physics

Lesson notes

Learning Objectives

Indicator: 2.3.2.LI.2 - Explain the torque on rectangular current carrying coil in a magnetic field.

By the end of the lesson, learners can:

Define torque and state its SI unit (newton-metre, N m) as it applies to a rotating coil.
Use the left-hand rule to predict the direction of forces on each side of a rectangular coil carrying current in a magnetic field.
Explain why the torque on a rectangular coil depends on the current, the number of turns, the area of the coil, the magnetic flux density, and the angle between the coil plane and the magnetic field.
Derive or reproduce the torque expression τ = n B I A cos θ and use it to explain why torque is maximum when the coil plane is parallel to the field and zero when perpendicular.
Construct a simple model of a current-carrying coil in a magnetic field and demonstrate how the twisting effect (couple) produces rotation.

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Curriculum details

Strand: Electric Field, Magnetic Field and Electronics (Strand 3)
Sub-strand: Electromagnetism (3.2)
Content standard: 2.3.2.CS.2 - Demonstrate knowledge and understanding of the forces set up between parallel current-carrying conductors in a uniform magnetic field and applications. 2.3.2.LO.2 Demonstrate the repulsive and attractive forces between parallel current-carrying conductors in a magnetic field.
Indicator: 2.3.2.LI.2 - Explain the torque on rectangular current carrying coil in a magnetic field.
Suggested placement: Semester 2, Week 8 (Week 28 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: NaCCA curriculum document, p. 128

Exemplars (from the NaCCA curriculum)

Project-Based Learning: Learners in pairs construct a basic electric motor and discuss its operation.
Provide equitable access to resources and opportunities.
Assessment (2.3.2.AS.2). The document marks these depth-of-knowledge levels for this indicator: Level 4 Extended critical thinking and reasoning.
Teaching and Learning Resources:
- Audio visuals
- Internet
- Projectors
- YouTube
- Interactive virtual laboratory