Electromagnetism and Electromagnetic Induction

Electromagnetism and Electromagnetic Induction

Electromagnetism

• Hans Oersted's Discovery: The principle of electromagnetism was first established by Hans Oersted, who demonstrated that an electric current causes a compass needle to deflect.
  • Key Insight: When electric current flows through a wire, it creates a magnetic field stronger than the Earth's magnetic field.

Direction of Magnetic Flux

• Right-Hand Rule: The direction of the magnetic field around a current-carrying wire can be determined using the right-hand rule.
  • Thumb Direction: Points along the current direction.
  • Fingertips Direction: Indicate the direction of the magnetic field lines.
• Current Flow: Electric current is regarded as positive flow while electrons move in the opposite direction.
• Looped Wire: Looping the wire enhances the magnetic field as the flux lines become concentrated.
• Solenoid Configuration: Coiling the wire into a solenoid further strengthens the magnetic field. Adding an iron core refines and concentrates the electromagnetic field , resulting in an electromagnet.

Direction of Magnetic Field

• Magnetic Field Direction: In a solenoid, the thumb of the right hand indicates the direction of the magnetic field as it exits the north pole, while the fingers show the current's direction.
• Magnetic Flux Lines: These curves demonstrate that the field exists in its entirety and diminishes with distance from the magnet, explaining the short-range effect of magnets.

Electromagnetic Induction

• Michael Faraday's Discovery: Faraday found that moving a conductor through a magnetic field generates a current within that conductor. This principle is known as electromagnetic induction.
  • Example: Moving a bar magnet into a coil of wire induces current, while moving it back and forth generates alternating current.

Number of Coils in the Conductor

• Impact on Voltage: Increasing the number of wire coils in a moving magnetic field boosts the induced voltage.
  • Example: Doubling the number of coils from two to four doubles the voltage.

Angle of Conductor

• Angle Relevance: The angle at which the wire moves in relation to the magnetic field affects the induced voltage.
  • Perpendicular Motion: Produces maximum voltage because it intersects more magnetic field lines than at an oblique angle.

Magnetic Field in a Conductor

• AC Characteristics: An alternating current (AC) creates a fluctuating magnetic field that expands and collapses as the direction of the current alternates.
  • Polarity Changes: The north and south poles switch with the alternating current, affecting the magnetic field properties.

Mutual Induction

• Induced Currents: If a second coil is placed near the coil producing a magnetic field, an alternating current will be induced in the second coil due to mutual induction.
  • Primary vs. Secondary Coil: The first coil that generates the magnetic field is the primary coil, and the second coil where current is induced is the secondary coil.

Lenz’s Law

• Induced Current Direction: Lenz's Law states that the direction of the induced current opposes the change causing it.
• Cutting Flux Lines: As the primary magnetic field expands, the induced current flows oppositely to oppose the change.

Self Induction

• AC Self-Induction: In alternating current, the primary and secondary currents fluctuate, creating a consistent secondary current that opposes the primary current. This is utilized in devices like autotransformers in x-ray circuits.

Review Questions

• Electromagnetism's Founder: Oersted.
• Induction Type: Mutual induction occurs when one coil induces a current in another.
• Self-Induction: Occurs within the same coil when the magnetic field fluctuates.
• Right-Hand Rule Application: Used to find the direction of magnetic flux.
• Voltage and Coil Movement: Doubling the speed increases induced voltage.
• Coils and Voltage Relationship: More coils lead to greater voltage induced.
• Right-Hand Rule with Coils: Thumb indicates the direction of the magnetic field if fingers show current direction.