Electromagnetic Induction | AP Physics C Electricity and Magnetism - Grade 9 PDF Download

Induced EMF

• An electromotive force (EMF) is produced in a conductor when there is relative motion between the conductor and a magnetic field.
• EMF can also be induced if the conductor remains stationary but is exposed to a changing magnetic field.
• When an electrical conductor moves within a fixed magnetic field, such as a wire cutting through magnetic field lines, it generates an EMF.

• Process of Inducing an EMF

  • As a magnet moves through a conductor (e.g., a coil), the magnetic field lines intersect with the turns of the conductor, inducing an EMF.
  • When the magnetic field changes, an EMF is generated in the coil due to the cutting of field lines.

• A sensitive voltmeter is a crucial tool for measuring induced EMF
• When a conductor forms a complete circuit, it induces a current detectable by an ammeter

Lenz's Law

• The Principle of Lenz's Law: Lenz's Law is a fundamental concept in electromagnetism that describes the direction of an induced electromotive force (emf) in a circuit. It states that the induced emf always opposes the change in magnetic flux that produces it.
• Opposing Changes: This means that when there is a change in magnetic flux through a circuit, an induced current will flow in such a way as to create a magnetic field that opposes the change in flux.
• Application in Practice: For instance, if a magnet is pushed into a coil of wire, the induced current will create a magnetic field that opposes the motion of the magnet. This action is in accordance with Lenz's Law.
• Generator Effect: When a magnet is moved towards a coil, the changing magnetic field induces a current in the coil. This induced current generates a magnetic field that resists the motion of the magnet, as described by Lenz's Law.

Demonstrating Lenz's Law

• When a magnet is pushed into a coil, a potential difference is induced in the coil due to the generator effect.
• Potential Difference: The induced potential difference always acts in a way that opposes the change causing it.
• Opposition: The coil exerts a force to resist the magnet being pushed into it.
• Pole Formation: The end of the coil nearest to the magnet becomes a north pole, resulting in repulsion of the magnet's north pole.

• If a magnet is pulled away from the coil, the end of the coil nearest to the magnet will become a south pole.
• South Pole Formation: The induced potential difference in the coil opposes the change and causes the end of the coil to act as a south pole, attracting the north pole of the magnet.
• Explanation:
  • When a coil is moved near a magnet, a potential difference is induced in the coil.
  • This induced potential difference always acts against the change that caused it.
  • The coil exerts a force to resist the motion of the magnet away from the coil.
  • As a result, the end of the coil closest to the magnet becomes a south pole.
  • This south pole end of the coil will attract the north pole of the magnet.

Right-Hand Dynamo Rule

• When a wire moves through a magnetic field, the Right-Hand Dynamo Rule helps determine the direction of the induced EMF.

Steps to Use the Rule:

• First Finger = Field:
• Begin by pointing the first finger (on the right hand) in the direction of the field.
• Thumb = Motion:
• Next, point the thumb in the direction that the wire is moving.

The Right-Hand Dynamo Rule simplifies the process of determining the direction of induced EMF when a wire moves through a magnetic field.