Electromagnetism and Basic Electrical Components: A Comprehensive Guide

Posted on Aug 26, 2024 in Physics

Electromagnetism and Basic Electrical Components

Input Sensors and Transducers

Thermistor

A thermistor is a temperature-dependent resistor. As temperature increases, its resistance decreases.

Light Dependent Resistor (LDR)

An LDR’s resistance decreases as light intensity increases.

Electrical Components

Capacitor

Capacitors store small amounts of electric charge. A higher capacitance (measured in microfarads – μF) indicates a greater charge storage capacity. They are commonly used in time-delay circuits.

Relay

A relay is a switch operated by an electromagnet.

Electromagnetic Induction

Methods of Inducing EMF

An electromotive force (EMF) can be induced in several ways:

1. Moving a Wire Across a Magnetic Field: Passing a wire through a magnetic field induces a small EMF. If the wire is part of a complete circuit, this EMF generates a current flow, detectable with a galvanometer. The induced EMF is proportional to the rate at which the magnetic field lines are cut by the conductor.

Increasing Induced EMF:

• Move the wire faster.
• Use a stronger magnet.
• Increase the length of wire within the magnetic field (e.g., by looping the wire).

Reversing Current and EMF Direction:

• Move the wire in the opposite direction.
• Reverse the magnet’s orientation to change the field direction.

Fleming’s Right-Hand Rule determines the current direction.

2. Moving a Bar Magnet into a Coil: Pushing a bar magnet into a coil that’s part of a circuit induces a current flow.

Increasing Induced EMF and Current:

• Move the magnet faster.
• Use a stronger magnet.
• Increase the number of turns in the coil.

Reversing Induced EMF and Current:

• Pull the magnet away from the coil.
• Use the magnet’s South pole instead of the North pole.

No EMF: Holding the magnet stationary results in no EMF.

Lenz’s Law: An induced current always opposes the change that produced it. When a magnet approaches a coil, the adjacent poles of the coil and magnet become the same. When the magnet moves away, the poles become opposite (opposite poles attract).

Right-Hand Grip Rule: This rule determines the pole type (North or South) based on the induced current direction. Fingers point in the conventional current direction, and the thumb indicates the North Pole.

The Magnetic Effect of a Current

Magnetic Field Around a Wire and Solenoid

1. Increasing the current strengthens the magnetic field.
2. Increasing the number of turns in a coil strengthens the field.
3. Reversing the current direction reverses the magnetic field direction (Right-Hand Rule).

Applications of the magnetic effect of current include relays and circuit breakers.

DC Motor

Principles of Operation

A current-carrying coil within a magnetic field experiences a turning effect. A DC motor operates on direct current. The coil, made of insulated copper wire, rotates freely between the magnet’s poles. The commutator (split-ring) is attached to the coil and rotates with it. When the coil passes the vertical position, the commutator reverses the current direction, ensuring continuous rotation. Carbon brushes maintain the coil’s connection to the battery.

Maximizing Turning Effect

• Increase the current.
• Use a stronger magnet.
• Increase the number of coils (effectively increasing coil length).
• Increase the coil’s area (also increasing coil length).

Reversing Rotation

• Reverse the battery polarity.
• Reverse the magnet’s poles.

Formulas

Key Formulas in Physics and Electricity: