Physics Unit 9 study games — Magnetism.
This unit covers magnetic fields, electromagnets and electromagnetic induction — essential concepts for Physics. Use our interactive study games to test your understanding, or review questions in traditional format below.
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This unit covers magnetic fields, electromagnets and electromagnetic induction — essential concepts for Physics. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Magnetic Fields
A magnetic field is a region around a magnet or moving charge where magnetic forces act. Students must know field line conventions, how to determine field direction, and the relationship between field strength and distance. Exams test the ability to draw and interpret field diagrams and apply the right-hand rule.
Key Points
- Magnetic field lines exit the north pole and enter the south pole; they never cross
- Closer field lines indicate stronger field strength
- Like poles repel, opposite poles attract
- Earth's geographic north pole is actually a magnetic south pole (the compass north-seeking end is attracted to it)
A compass is placed 5 cm to the right of a bar magnet's north pole. Which direction does the compass needle point?
Field lines exit the north pole of the bar magnet and extend outward. The compass needle aligns with the local field direction, so the north-seeking end of the compass points away from the bar magnet's north pole — that is, to the right. The compass needle points away from the magnet.
2 Electromagnets
An electromagnet is created when electric current flows through a coil of wire (solenoid), producing a magnetic field. Students must know how to determine the field direction using the right-hand rule and what factors affect field strength. Exams often ask how changing current, turns, or core material changes the electromagnet.
Key Points
- Right-hand rule for a solenoid: curl fingers in the direction of current flow; thumb points to the north pole
- Field strength increases with more current, more turns of wire, and a ferromagnetic core (e.g., iron)
- Electromagnets can be turned on/off, unlike permanent magnets
- The north pole of the electromagnet is the end where field lines exit
A solenoid has 50 turns and carries 2 A of current. How can you double the magnetic field strength without changing the current?
Magnetic field strength in a solenoid is proportional to both current and the number of turns per unit length. Since current is fixed, doubling the number of turns from 50 to 100 (while keeping the same length) doubles the field strength. Alternatively, inserting an iron core would also significantly increase the field.
3 Electromagnetic Induction
Electromagnetic induction is the production of a voltage (EMF) in a conductor when the magnetic flux through it changes. Students must understand Faraday's Law — that induced EMF depends on the rate of change of flux — and Lenz's Law, which determines the direction of the induced current. These concepts underlie generators and transformers, which are common exam topics.
Key Points
- Faraday's Law: greater rate of change of magnetic flux → greater induced EMF
- Lenz's Law: induced current flows in a direction that opposes the change in flux that caused it
- Ways to increase induced EMF: move the magnet faster, use a stronger magnet, add more turns to the coil
- Generators convert mechanical energy to electrical energy using induction; transformers change voltage levels
A magnet is pushed north-pole-first into a coil of wire connected to a galvanometer. The galvanometer deflects right. What happens to the deflection when the magnet is pulled back out?
When the magnet enters, flux through the coil increases, inducing a current that opposes the increase (Lenz's Law) — this causes the rightward deflection. When the magnet is pulled out, the flux decreases, so the induced current reverses direction to oppose the decrease. The galvanometer now deflects to the left.
Questions, answered.
What is Magnetism?
Magnetism is Unit 9 of Physics, covering magnetic fields, electromagnets and electromagnetic induction.
How to study for Physics Unit 9?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 25+ review questions across 5 different game modes.