IB MYP 4-5 Physics- Electromagnetic induction - Study Notes - New Syllabus
IB MYP 4-5 Physics-Electromagnetic induction – Study Notes
Key Concepts
- Electromagnetic induction
Electromagnetic Induction
Electromagnetic Induction
Electromagnetic induction is the process of generating an electromotive force (emf) or current in a conductor when it is placed in a changing magnetic field.
- Discovered by Michael Faraday in 1831.
- No battery is required → the induced current is produced by motion or changing magnetism.
Faraday’s Law of Induction
An emf is induced in a conductor when the magnetic flux</strong through it changes.
- The induced emf is proportional to the rate of change of magnetic flux</strong.
\(\text{emf} \propto \dfrac{d\Phi_B}{dt}\)
- \(\Phi_B\) = magnetic flux = \(B \times A \times \cos\theta\)
- \(B\) = magnetic field strength
- \(A\) = area of coil
- \(\theta\) = angle between field and coil
Lenz’s Law
The direction of the induced current is such that it opposes the change in magnetic flux</strong that caused it.
- This is an example of the law of conservation of energy.
Factors Affecting Induced emf
- Strength of magnetic field (\(B\)) – stronger field → larger emf.
- Speed of motion (faster change → larger emf).
- Number of turns in coil (more turns → greater emf).
- Angle of coil relative to field.
Applications of Electromagnetic Induction
- Electric generators – convert mechanical energy → electrical energy.
- Transformers – change voltage in AC circuits.
- Induction cookers – heat pans using induced currents.
- Credit card readers – detect magnetic strips by induction.
Example:
A bar magnet is pushed into a coil. A galvanometer connected to the coil shows a deflection. What happens when the magnet is pulled out?
▶️ Answer/Explanation
Step 1: When magnet moves → magnetic flux in coil changes → emf induced.
Step 2: Galvanometer shows current (direction depends on direction of flux change).
Step 3: Pushing magnet in → current in one direction; pulling out → current in opposite direction.
Final Answer: Current reverses when magnet is pulled out of the coil.
Example:
A rectangular coil is rotated in a magnetic field. Explain how this produces electricity.
▶️ Answer/Explanation
Step 1: Rotation changes angle \(\theta\) between coil and field → magnetic flux changes.
Step 2: Changing flux induces emf in coil (Faraday’s law).
Step 3: Direction of current alternates every half turn (Lenz’s law).
Final Answer: Continuous rotation produces alternating current (AC), which is the principle of a generator.
Example:
A metal ring is placed above a solenoid carrying an increasing current. The ring is observed to jump upwards. Explain why.
▶️ Answer/Explanation
Step 1: Increasing current in solenoid → increasing magnetic flux through the ring.
Step 2: Induced current in ring produces its own magnetic field (Lenz’s law).
Step 3: Induced field opposes the increase → ring experiences repulsive force.
Final Answer: The ring jumps upward due to opposing induced current resisting the flux change.