Lesson 09
Test
Assess understanding of magnetic fields and induction.
Objectives
Lesson outcomes
- Assess use of magnetic force equations and direction rules.
- Assess understanding of Hall probes, magnetic flux, and electromagnetic induction.
- Identify which B4 skills need correction or further practice.
Syllabus
CIE 9702 syllabus points
19 linked
- 20.1.1 understand that a magnetic field is an example of a field of force produced either by moving charges or by permanent magnets
- 20.1.2 represent a magnetic field by field lines
- 20.2.1 understand that a force might act on a current-carrying conductor placed in a magnetic field
- 20.2.2 recall and use the equation F = BIL sin θ, with directions as interpreted by Fleming’s left-hand rule
- 20.2.3 define magnetic flux density as the force acting per unit current per unit length on a wire placed at right‑angles to the magnetic field
- 20.3.1 determine the direction of the force on a charge moving in a magnetic field
- 20.3.2 recall and use F = BQv sin θ
- 20.3.3 understand the origin of the Hall voltage and derive and use the expression VH = BI / (ntq), where t = thickness
- 20.3.4 understand the use of a Hall probe to measure magnetic flux density
- 20.3.5 describe the motion of a charged particle moving in a uniform magnetic field perpendicular to the direction of motion of the particle
- 20.3.6 explain how electric and magnetic fields can be used in velocity selection
- 20.4.1 sketch magnetic field patterns due to the currents in a long straight wire, a flat circular coil and a long solenoid
- 20.4.2 understand that the magnetic field due to the current in a solenoid is increased by a ferrous core
- 20.4.3 explain the origin of the forces between current-carrying conductors and determine the direction of the forces
- 20.5.1 define magnetic flux as the product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density
- 20.5.2 recall and use Φ = BA
- 20.5.3 understand and use the concept of magnetic flux linkage
- 20.5.4 understand and explain experiments that demonstrate: • that a changing magnetic flux can induce an e.m.f. in a circuit • that the induced e.m.f. is in such a direction as to oppose the change producing it • the factors affecting the magnitude of the induced e.m.f.
- 20.5.5 recall and use Faraday’s and Lenz’s laws of electromagnetic induction
Definitions
Required definitions
Magnetic flux density
the force acting per unit current per unit length on a wire placed at right angles to the magnetic field.
Magnetic flux
magnetic flux density multiplied by the cross-sectional area perpendicular to the field.
Lesson Notes
Student guidance and lesson notes
Overview
This lesson assesses your understanding of B4 magnetic fields and induction. Expect a mix of definitions, diagrams, direction rules, calculations, practical reasoning, and written explanations.
What You Need to Know
- Magnetic force questions may involve a current-carrying conductor or a moving charge.
- Field-line diagrams and direction rules must be clear and unambiguous.
- Hall effect questions connect charge-carrier motion to a measurable Hall voltage.
- Induction questions require careful use of flux, flux linkage, Faraday’s law, and Lenz’s law.
- Written explanations should identify the change that causes the induced e.m.f.
How to Work Through It
- Check the formula sheet and note which equations still require careful interpretation.
- Complete the assessment independently under the agreed conditions.
- Show working clearly, including directions, units, and substitutions.
- After marking, record the specific B4 skill behind each error.
Check Your Understanding
- Did you choose the correct magnetic force equation?
- Did you state directions using a clear rule or diagram?
- Did you explain Lenz’s law in terms of opposing the change?
- Did your calculations use SI units and appropriate significant figures?
Common Mistakes
- Treating induction direction as a guess instead of a consequence of Lenz’s law.
- Missing angle factors in magnetic force calculations.
- Giving vague explanations of Hall voltage or magnetic flux linkage.
- Losing units when using small charges, currents, or areas.
Next Steps
- Bring marked work into the review lesson.
- Prepare corrections by grouping errors into calculation, diagram, and explanation skills.