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CIE iGCSE Co-ordinated Sciences-P4.5.1 Electromagnetic induction- Study Notes- New Syllabus

CIE iGCSE Co-ordinated Sciences-P4.5.1 Electromagnetic induction – Study Notes

CIE iGCSE Co-ordinated Sciences-P4.5.1 Electromagnetic induction – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.

Key Concepts:

Supplement

  • Know that a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an e.m.f. across the conductor
  • State the factors affecting the magnitude of an induced e.m.f.

CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics

Electromagnetic Induction

 An electromotive force (e.m.f.) is induced across a conductor when:

  • A conductor moves across a magnetic field, or
  • The magnetic field linking with a conductor changes (e.g., by moving a magnet or changing current in a nearby coil).

Explanation:

  • Electrons in a conductor experience a force when they move through a magnetic field.
  • This causes them to move, producing an induced potential difference (e.m.f.).
  • If the conductor is part of a closed circuit, this e.m.f. drives an induced current.

Conditions for Induction:

  • The conductor must cut magnetic field lines (motion relative to the field is required).
  • No e.m.f. is induced if the conductor moves parallel to the field lines.
  • The induced e.m.f. is larger if:
    • The magnetic field is stronger.
    • The conductor moves faster.
    • The length of conductor in the field is greater.

Everyday Applications:

  • Bicycle dynamo: Coil and magnet movement induces e.m.f. to light a lamp.
  • Electric generators: Rotating coils in magnetic fields produce electricity in power stations.
  • Microphones: Sound vibrations move a coil in a magnetic field, inducing a varying e.m.f. (sound signal).

Summary Statement:

A conductor moving across a magnetic field, or a changing magnetic field linking with a conductor, induces an e.m.f. across the conductor. If the circuit is closed, an induced current flows.

Example :

What happens if you move a straight wire downwards between the poles of a horizontal magnetic field?

▶️ Answer/Explanation

Step 1: The wire is cutting through magnetic field lines.

Step 2: An e.m.f. is induced across the ends of the wire.

Step 3: If the wire is connected in a circuit, a current will flow.

Final Answer: A downward motion across the field induces an e.m.f. across the wire; if in a circuit, an induced current flows.

Fleming’s Right-Hand Rule (Generator Rule)

 Fleming’s Right-Hand Rule is used to predict the direction of induced current when a conductor cuts through magnetic field lines.

The Rule:

  • Hold the right hand with the thumb, first finger, and second finger all at right angles to each other.
  • Thumb (Motion): Points in the direction of the conductor’s motion (relative to the field).
  • First Finger (Field): Points in the direction of the magnetic field (from North → South).
  • Second Finger (Current): Gives the direction of the induced current (conventional current, positive → negative).

Key Notes:

  • This rule applies to generators (induced current), not to motors (which use Fleming’s Left-Hand Rule).
  • The three directions (motion, field, current) are all mutually perpendicular.

Everyday Example:

  • In a bicycle dynamo, the coil or magnet moves, cutting magnetic field lines. Using Fleming’s Right-Hand Rule allows prediction of the direction of the induced current, which powers the lamp.

Quick Memory Aid:

“M” for Motion → Thumb, “F” for Field → First finger, “C” for Current → Second finger.

Example :

A straight wire is pushed downward between the poles of a horizontal magnetic field directed from left to right. Predict the direction of the induced current using Fleming’s Right-Hand Rule.

▶️ Answer/Explanation

Step 1: Thumb = motion (downwards).

Step 2: First finger = magnetic field (left to right).

Step 3: Second finger = current direction → into the page.

Final Answer: The induced current flows into the page.

Factors Affecting the Magnitude of an Induced e.m.f.

The size of the induced e.m.f. depends on how quickly magnetic field lines are cut or how fast the magnetic flux linking the conductor changes.

Main Factors:

  • Speed of Motion: Faster movement of the conductor or magnet → field lines cut more quickly → larger e.m.f.
  • Strength of Magnetic Field: A stronger field provides more flux lines to cut → larger e.m.f.
  • Length of Conductor in the Field: Longer wire/coil in the magnetic field → more electrons affected → larger e.m.f.
  • Number of Turns in the Coil: More turns in a coil → each turn has an induced e.m.f. → total induced e.m.f. increases.
  • Rate of Change of Magnetic Flux: The faster the magnetic flux linkage changes, the greater the induced e.m.f. (∝ rate of change).
FactorEffect on Induced e.m.f.
Speed of MotionFaster motion → larger e.m.f.
Magnetic Field StrengthStronger field → larger e.m.f.
Length of Conductor in FieldLonger conductor → larger e.m.f.
Number of Coil TurnsMore turns → induced e.m.f. adds up → larger total e.m.f.
Rate of Flux ChangeFaster flux change → greater e.m.f.

Example :

A magnet is pushed quickly into a coil, then slowly. In which case is the induced e.m.f. larger? Why?

▶️ Answer/Explanation

Step 1: The induced e.m.f. depends on the rate of change of magnetic flux through the coil.

Step 2: A fast push → flux changes more rapidly → larger e.m.f.

Step 3: A slow push → flux changes more slowly → smaller e.m.f.

Final Answer: The induced e.m.f. is larger when the magnet is pushed in quickly.

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