Electromagnetic forces and induction Notes

What Happens When An Electric Current Flows Through A Wire Placed In A Magnetic Field?

1. When an electric current flows through a wire placed in a magnetic field, the wire experiences a force.
2. This force causes the wire to move sideways rather than along the direction of the current.
3. The force acts without physical contact, showing that magnetic fields can cause effects at a distance.
4. This interaction between a current and a magnetic field is called the motor effect.
5. The motor effect explains how electrical energy can be converted into motion.

Why does the wire experience a force?

1. A current-carrying wire produces its own magnetic field around it.
2. When the wire is placed in an external magnetic field, the two magnetic fields interact.
3. On one side of the wire, the magnetic fields reinforce each other.
4. On the opposite side, the magnetic fields oppose each other.
5. This imbalance in magnetic field strength produces a sideways force on the wire.

Analogy:
The wire moves like a boat being pushed sideways by stronger water flow on one side than the other.

Direction of the Force

1. The force acts at right angles to:
   1. The direction of the current
   2. The direction of the magnetic field
2. This means the conductor does not move along the field lines or along the current direction.

Reversing the Force

1. If the direction of the current is reversed, the direction of the force also reverses.
2. If the direction of the magnetic field is reversed, the direction of the force also reverses.
3. Reversing both the current and the magnetic field results in the force acting in the same original direction.

What does Fleming’s Left-Hand Rule explain?

1. Fleming’s left-hand rule is used to predict the direction of the force on a current-carrying conductor.
2. It is a prediction tool, not an explanation of why the force exists.
3. The rule is commonly used in questions involving electric motors.

How does Fleming’s Left-Hand Rule work?

1. Hold the left hand with the thumb, first finger, and second finger at right angles.
2. The first finger represents the magnetic field direction (north to south).
3. The second finger represents the current direction (positive to negative).
4. The thumb shows the direction of the force or motion.

Forces on a Current-Carrying Coil

1. A coil consists of several straight sections of wire.
2. When current flows through the coil in a magnetic field:
   1. One side of the coil experiences a force upward.
   2. The opposite side experiences a force downward.
3. These forces act in opposite directions, producing a turning effect.

Why the Coil Rotates

1. The forces do not cancel out because they act at different positions.
2. This causes the coil to rotate rather than move in a straight line.
3. Rotation continues as long as:
   1. Current flows
   2. A magnetic field is present

Energy Changes

1. Electrical energy supplied to the coil is converted into kinetic energy of rotation.
2. Some energy is also transferred as thermal energy due to resistance in the wire.

Electromagnetic Induction Happens When Magnetic Fields Change

1. Electromagnetic induction occurs when an electric current is produced in a conductor due to motion in a magnetic field.
2. Unlike the motor effect, no external power supply is needed to create the current.
3. The current is generated only when there is relative motion between the conductor and the magnetic field.
4. This process explains how generators produce electrical energy.

"Cutting Field Lines" Is A Useful Model

1. One way to picture induction is to imagine a wire cutting through magnetic field lines.
2. The more field lines cut per second, the larger the induced voltage, and (in a closed circuit) the larger the induced current.
3. This can be increased by:
   1. moving the wire faster
   2. using a stronger magnetic field (field lines closer together)
   3. using more turns of wire in a coil, so more wire passes through the field
4. If a wire is held stationary in a steady (unchanging) magnetic field, there is no induced voltage because it does not cut through field lines.

Induced Current and Induced Voltage

1. When a conductor cuts through magnetic field lines, charges inside the conductor experience a force.
2. This force causes charges to move, producing an induced current.
3. If the circuit is open, an induced voltage is produced instead of a current.

Conditions Required for Induction

1. A magnetic field must be present.
2. There must be relative motion between the magnetic field and the conductor.
3. Alternatively, the magnetic field strength must change.

Why Does Movement Matter In Electromagnetic Induction?

1. An induced current occurs if:
   1. A magnet is moved into or out of a coil.
   2. A coil is moved near a magnet.
2. It does not matter which object moves; only the relative motion matters.

Direction of Motion and Induced Current

1. The direction of the induced current depends on:
   1. The direction of motion.
   2. The orientation of the magnetic field.
2. Reversing the motion reverses the direction of the induced current.