Grade 10 electricity Electrical Machines – Electro-Magnetism Notes

1. Explain the principle of electro‑magnetism in electrical technology.
2. Draw magnetic field pattern of a current‑carrying conductor.
3. Construct electromagnetic devices for a given application.
4. Test the functionality of electromagnetic devices in electrical appliances for optimal efficiency.
5. Appreciate the importance of electromagnetism in electrical devices.
6. Identify principles, magnetic field patterns, device construction, device testing and applications as categories of electro‑magnetism.

1. Principle of electro‑magnetism (simple)

When electric current flows, it produces a magnetic field around the conductor. This is the principle of electro‑magnetism. The strength and shape of the magnetic field depend on:

• Amount of current (more current → stronger field)
• Number of turns of wire (coil/solenoid → stronger, concentrated field)
• Presence of a magnetic core (iron core concentrates and strengthens the field)

Everyday examples in Kenya: the starter motor and alternator in a matatu, loudspeakers in a radio, electric bells in a school, and the transformer on a power pole.

2. Magnetic field patterns — simple drawings (use these in your notebook)

3. Simple electromagnetic devices — how to build (class practical)

A) Simple electromagnet (safe classroom model)

Materials: a large iron nail, insulated copper wire (enamelled, 26–20 AWG), 2 × AA batteries (or 1 × 9V with care), tape, small paperclips.

Steps:

1. Strip ends of the wire (expose copper) and wrap the wire tightly around the nail in many turns (20–50 turns). Leave 10–15 cm free at each end.
2. Connect the ends to the battery terminals (use tape), forming a closed circuit. The coil becomes magnetised — test by picking up paperclips.
3. To switch on/off, break the circuit (use a simple switch or remove one battery connection).

Safety: Do not leave connected for long — wire may heat. Use low voltage (AA batteries) for classroom work.

B) Simple relay / buzzer idea (demonstration)

Use a coil, an iron core and a spring‑loaded contact to show how current can move a contact and switch another circuit. Materials and teacher guidance required for safe build.

C) Real applications to try (guided group projects)

• Electric bell model (coil + hammer + contact)
• Small DC motor demonstration (remove magnet and show coil rotation)
• Simple loudspeaker demo: coil on paper, magnet under it, apply audio frequency signal (teacher demonstration).

4. Testing and ensuring optimal efficiency

What to test on an electromagnet or coil:

1. Continuity/resistance: Use a multimeter to check the coil is continuous (low resistance). An open circuit = broken wire.
2. Current draw: Measure current when connected. Excessive current → overheating and wasted energy.
3. Functional test: Attach target object (paperclips) and observe hold force. Compare when using different numbers of turns or cores.
4. Heat check: Run for a short time and feel coil temperature (careful!). Hot coils mean inefficiency/overload.
5. Insulation check: Ensure wire enamel or tape is intact; shorted turns reduce field and cause heating.

Improving efficiency: increase turns, use thicker wire for heavy currents, use soft iron core, minimize shorted turns, provide cooling where needed.

5. Importance & applications (why learners should care)

• Electromagnetism is the basis of electric motors and generators — used in transport (vehicles), industry and household appliances.
• Relays and contactors that control high current circuits use electromagnets (important in power distribution and machines).
• Transformers (part of national grid) use magnetism to change voltages for safe distribution—seen on power poles in Kenya.
• Loudspeakers, microphones, and mobile device components depend on electromagnetic principles.

6. Classroom & suggested learning experiences (practical, group and assessment ideas)

1. Demonstration: Teacher shows a straight wire with current and uses compass to show circular field; learners draw pattern.
2. Practical group task: Build a small electromagnet and test how many paperclips it lifts. Change number of turns and record results in a table.
3. Drawing exercise: Students draw magnetic fields for straight conductor and solenoid, label directions using right‑hand rule.
4. Project: In groups design and build a working bell or relay model using safe low voltage supplies. Present working principle.
5. Field visit / local link: Visit a local power substation, transformer site or motor repair shop (with permission) to see electromagnetism in action.
6. Assessment: Short written quiz on SLOs, practical checklist during construction, group presentation and peer assessment.

Materials locally available in Kenya: iron nails, copper wire from scrap cables, old batteries, small switches, paperclips, cheap multimeter (for school labs) and scrap magnets.

7. Quick troubleshooting checklist (when a device fails)

• No magnetism: check battery/voltage, open circuit in coil, broken wire, poor connections.
• Weak magnetism: few turns, low current, wrong core material (use soft iron), insulation shorting turns.
• Overheating: too much current for wire size or shorted turns. Reduce voltage, increase wire thickness, add cooling breaks.

8. Short glossary (useful terms)

Current

Flow of electric charge (measured in amperes, A).

Magnetic field

Region around a magnet or current where magnetic forces act (drawn as field lines).

Solenoid

Coil of wire producing a magnetic field when current flows.

Electromagnet

A magnet produced by current in a coil, often with an iron core to strengthen the field.

Right‑hand rule

Rule to find direction of magnetic field: thumb = current, curled fingers = field direction.

9. Assessment ideas aligned to SLOs

• Written: Explain principle and draw field patterns (SLO a, b).
• Practical: Build and demonstrate an electromagnet that lifts N paperclips (SLO c, d).
• Oral or poster: Describe applications and classify concepts into the categories listed in SLO f (SLO e, f).