CBSE Notes Class 10 Science Chapter 12 - Magnetic Effects of Electric Current

The magnetic effect of current is a key principle in electromagnetism that explains how an electric current creates a magnetic field. First identified by Hans Christian Oersted in 1820, this phenomenon is crucial for grasping the connection between electricity and magnetism. When electric current passes through a conductor, it produces a surrounding magnetic field.

1.0Oersted’s Experiment

• They found that a compass needle is deflected when an electric current travels through a metallic wire placed nearby.
• Observations show that electricity and magnetism were related phenomena.
• It is established that there are two sources of magnetism namely, electric current and permanent magnet.

2.0Magnetic Field and Magnetic Field Lines

• Magnetic Field: The magnetic field is the area around a magnet where its influence affects other magnetic materials. It is measured in Teslas (T).
• Magnetic Field Lines: These lines extend from the north pole of a magnet, curve around, and return to the south pole  forming closed loops. They are densest near the poles and never intersect. The direction of the magnetic field at any point is indicated by the tangent to the field lines at that point.

3.0Magnetic Field around a Current Carrying Straight Conductor

When an electric current transfers through a straight conductor, it generates a magnetic field around it, which is invisible but can be detected with a magnetic compass. Increasing the current causes greater deflection of the compass needle. The magnetic field lines form concentric circles centered on the wire and lie in a plane perpendicular to its length. The field strength is stronger near the conductor and weakens with distance from it.

Right Hand Thumb Rule

The Right-Hand Thumb Rule identifies the direction of the magnetic field around a current-carrying conductor. To use it:

• Hold the wire with your right hand.
• Point your thumb in the direction of the current.
• Your curled fingers show the direction of the magnetic field lines, which form concentric circles around the wire.

4.0Magnetic Field Around a Circular Conductor with Electric Current

• The magnetic field formed by a current-carrying wire at a specific point is directly proportional to the amount of current flowing through it.
• If a circular coil has n  turns, the magnetic field it produces is n times greater than the field generated by a single turn

5.0Magnetic Field established by Current Flowing Through a Solenoid

A solenoid is a coil consisting of numerous circular loops of insulated copper wire wound closely in a cylindrical shape. One end acts as the magnetic north pole and the other as the south pole. Inside the solenoid, the magnetic field lines are parallel and straight, indicating a uniform magnetic field throughout its interior.

6.0Force on a Current Conveying Conductor in a Magnetic Field

•  A current conveying conductor placed in a magnetic field experiences a force that is right angled to both the direction of the current and the magnetic field.
• The direction of the force changes when the current direction in the conductor is reversed.

Fleming Left Hand Rule

It dictates the force direction on a current-carrying conductor in a magnetic field.

• Hold your left hand with the first finger, second finger, and thumb perpendicular to each other. 
• Align the first finger with the magnetic field direction, point the second finger in the current direction, and your thumb will show the direction of the force on the conductor.

7.0Domestic Electric Circuits

• Electric power to a house is supplied via overhead wires or underground cables with three insulated wire
• Live Wire (Brown or Red): Delivers current to the house.
• Neutral Wire (Light Blue or Black): Returns current and is at zero potential.
• Earth Wire (Green or Yellow): Grounds the system for safety.
• The voltage between the live and neutral wires is 220V. At the substation, the neutral and earth wires are connected to ensure they are at the same potential.
• Before entering the house, the supplier installs a fuse in the live wire, rated according to the house's load. The power then passes through an energy meter, which records usage in kilowatt-hours (kWh), with its earth wire grounded locally.
• The meter’s power lines connect to a distribution board that routes electricity through fuses to different parts of the house. Typically, one circuit has a higher current rating for heavy appliances like geysers and air coolers, while another has a lower rating for lights and fans.
• Appliances are connected in parallel across the live and neutral wires, each with its own switch. This ensures each appliance gets a consistent 220V and can operate independently.
• An electric fuse protects the circuit by breaking it if the current exceeds safe levels, melting due to Joule heating to prevent damage.
• Short Circuit-A short circuit occurs when electric current flows through an unintended low-resistance path, typically due to a direct connection between the live and neutral wires.
• Overloading-Overloading happens when too many appliances are connected to a single circuit or when appliances exceed the circuit's current capacity.