Magnetic Effects of Electric Current - Detailed Notes

Chapter focuses on magnetic effects of electric current.
Previous chapter covered heating effects of electric current.
Explores the relationship between electricity and magnetism.
Discusses electromagnets and electromagnetic effects.
Activity 12.1 demonstrates that an electric current through a copper wire produces a magnetic effect, deflecting a nearby compass needle.
Hans Christian Oersted discovered in 1820 that electric current deflects a compass needle, linking electricity and magnetism.
Oersted's research led to technologies like radio, television, and fiber optics.
The unit of magnetic field strength is named 'oersted' in his honor.

A compass needle is a small bar magnet that aligns with Earth's magnetic field.
The north end of a compass needle points towards the north, and the south end points towards the south.
Like poles of magnets repel each other, while unlike poles attract.
Activity 12.2 demonstrates that iron filings arrange themselves in a pattern around a bar magnet due to the magnetic field.
The region surrounding a magnet where its force can be detected is called a magnetic field.
Magnetic field lines represent the magnetic field; iron filings align along these lines.
Activity 12.3 explains how to draw magnetic field lines using a compass needle.
Magnetic field lines emerge from the north pole and merge at the south pole.
Inside the magnet, the direction of field lines is from the south pole to the north pole, forming closed curves.
The strength of the magnetic field is indicated by the closeness of the field lines; closer lines mean a stronger field.
No two magnetic field lines intersect each other because a compass needle would point in two directions at the intersection, which is impossible.
Magnetic field is a quantity that has both direction and magnitude.

Activity 12.1 demonstrated that electric current through a metallic conductor produces a magnetic field.
Activity 12.4 investigates the magnetic field around a straight conductor carrying current.
The direction of the magnetic field is reversed when the direction of the current is reversed.
Activity 12.5 investigates the magnetic field produced by a current through a straight conductor.
The magnitude of the magnetic field increases as the current through the wire increases.
The magnetic field decreases as the distance from the conductor increases.
The magnetic field lines around a current-carrying straight wire are concentric circles.
The direction of the magnetic field lines can be found using a compass needle.

The right-hand thumb rule provides a convenient way to find the direction of the magnetic field around a current-carrying conductor.
If you hold a current-carrying straight conductor in your right hand with your thumb pointing in the direction of the current, then your fingers will wrap around the conductor in the direction of the magnetic field lines.
Example 12.1 illustrates how to apply the right-hand thumb rule to determine the direction of the magnetic field around a horizontal power line.
Maxwell’s corkscrew rule describes the direction of the magnetic field as the direction of rotation of a corkscrew being driven in the direction of the current.

The magnetic field produced by a current-carrying straight wire depends inversely on the distance from it.
At the center of a current-carrying circular loop, the arcs of the magnetic field lines appear as straight lines.
Every point on the wire carrying current contributes to the magnetic field lines in the same direction within the loop.
If there is a circular coil having $n$ turns, the field produced is $n$ times as large as that produced by a single turn because the current in each turn has the same direction.
Activity 12.6 demonstrates the magnetic field produced by a current-carrying circular coil.

A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder.
The pattern of the magnetic field lines around a current-carrying solenoid is similar to that of a bar magnet.
One end of the solenoid behaves as a magnetic north pole, while the other behaves as the south pole.
The magnetic field inside the solenoid is uniform, indicated by parallel straight lines.
A strong magnetic field inside a solenoid can be used to magnetize a piece of magnetic material, like soft iron, when placed inside the coil, forming an electromagnet.

Andre Marie Ampere suggested that a magnet must exert an equal and opposite force on a current-carrying conductor.
Activity 12.7 demonstrates the force due to a magnetic field acting on a current-carrying conductor.
The direction of the force is reversed when the direction of current or the direction of the magnetic field is reversed.
The force is the highest when the direction of current is at right angles to the direction of the magnetic field.
Fleming’s left-hand rule is used to find the direction of the force on the conductor.
Electric motors, electric generators, loudspeakers, microphones, and measuring instruments use current-carrying conductors and magnetic fields.
Example 12.2 illustrates how to apply Fleming’s left-hand rule to determine the direction of force on an electron entering a magnetic field.

Homes receive electric power through a main supply via overhead electric poles or underground cables.
The live wire (positive) usually has red insulation, and the neutral wire (negative) has black insulation.
In the country being discussed, the potential difference between the live and neutral wires is 220 V.
The wires pass into an electricity meter and then through a main fuse.
Two separate circuits are often used: one of 15 A for high-power appliances and one of 5 A for lights and fans.
The earth wire (green insulation) is connected to a metal plate deep in the earth and is used as a safety measure for appliances with metallic bodies.
The earth wire provides a low-resistance path, ensuring that any leakage of current keeps the appliance's potential at earth level, preventing electric shock.
Appliances are connected parallel to each other, ensuring each has an equal potential difference.
An electric fuse prevents damage due to overloading, which can occur when live and neutral wires come into direct contact (short-circuiting) or due to a fault in the appliance.
The fuse melts to break the circuit, preventing damage from high electric current.
Overloading can also occur due to a hike in supply voltage or connecting too many appliances to a single socket.

Electric currents, even weak ion currents in nerve cells, produce magnetic fields.
The heart and brain produce significant magnetic fields.
Magnetic fields inside the body are used to obtain images of different body parts using Magnetic Resonance Imaging (MRI), aiding in medical diagnosis.