Class 10 Science

Chapter 13 Magnetic Effect of Electric Current

The magnetic effect of electric current, also known as electromagnetism, is a fundamental physical phenomenon that describes the relationship between electric currents and magnetic fields. This phenomenon was first discovered and explained by scientists like Hans Christian Oersted.

Oersted’s Experiment: In 1820, Hans Christian Oersted observed that an electric current passing through a conductor (such as a wire) produces a magnetic field around it. He discovered this when he noticed that a compass needle placed near a current-carrying wire deflected from its usual north-south direction.

Oersted placed a wire carrying an electric current (usually from a battery) close to a magnetic compass. The compass needle initially pointed in a particular direction, aligned with the Earth’s magnetic field.

When the electric current was turned on, Oersted noticed that the compass needle deflected from its original orientation. The direction of the deflection depended on the direction of the current in the wire.

Oersted also found that if he reversed the direction of the current in the wire, the compass needle’s deflection reversed as well. This indicated that the relationship between electric currents and magnetic fields was bidirectional.

Magnetic field and field lines: A magnetic field is a region surrounding a magnet, in which the force of the magnet can be detected, is said to have a magnetic field.

Magnetic field lines are imaginary lines used to represent the direction and strength of a magnetic field. They are used to visualize the pattern of the magnetic field.

When the iron fillings are sprinkled, the iron fillings arrange themselves in a pattern. The lines along which the iron filings align themselves represent magnetic field lines.

Properties of Magnetic field Lines :

• Magnetic field is a quantity that has both direction and magnitude.
• Field lines form closed loops.
• The density of field lines near a magnet’s pole is greater, indicating a stronger magnetic field in that region.
• Field lines do not intersect. This means that two magnetic field lines cannot cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.
• Field lines tend to align themselves along the direction of the magnetic field.
• The closer the field lines are to each other, the stronger the magnetic field in that region.
• Field lines always point from the north pole to the south pole. The field lines emerge from north pole and merge at south pole. And inside the magnet, the direction of direction of field lines is from its south pole to north pole.

Magnetic field due to a Current-carrying conductor –

1. Magnetic field due to a current through a Straight Conductor –

Shape of conductor – In a straight line

Pattern of the magnetic field – The magnetic field will be in concentric circles indicating the field lines of the magnetic field around a straight conducting wire.

The direction of the magnetic field lines – It is on the basis of the Right-hand thumb rule. When the current is in upward direction, magnetic field lines will be in anti-clockwise direction. And when the current is in the downward direction, magnetic field lines will be in clockwise direction.

Some factors on which the magnetic field depends –

1. If the current increases, the strength of the magnetic field also increases. If the current decreases, the strength of the magnetic field also decreases. That means the magnetic field is directly proportional to the current.

B  ∝ I

Where B is magnetic field and I is the electric current.

• The strength of magnetic field depends on the distance from the magnet. If compass will be closer to the magnet then magnetic field will be stronger. So

B  ∝ 1/d

Right hand Thumb Rule –

The right-hand rule helps to find the direction of the magnetic field around a current-carrying wire.

If you hold a current-carrying wire in your right hand with your thumb pointing in the direction of the current, then the direction of your    curled fingers indicates the direction of the magnetic field lines.

Magnetic Field due to a current through a Circular Loop

Shape of conductor – In a Circular Loop

Pattern of the magnetic field – The magnetic field will be in concentric circles indicating the field lines of the magnetic field around the circular loop, it would become larger and larger as we move away from the wire. By the time we reach at the centre of the circular loop, field lines arc gets more big circles which appears as straight lines.

The direction of the magnetic field lines – By Right-hand thumb rule, every section of the wire contributes to the magnetic field lines in the same direction withing the loop.

Some factors on which the magnetic field depends –

1. The magnetic field produced by a current-carrying wire at a given point depends directly on the current passing through it.
2. If there is a circular coil having n turns, the field produced is n times as large as that produced by a single turn. This is because the current in each circular turn has the same direction, and the field due to each turn then just adds up.
• Magnetic field due to a current in a solenoid –

A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.

Shape of conductor – In a solenoid.

The pattern of the magnetic field is like a bar magnet. The solenoid’s one end behaves as a magnetic north pole while the other end behaves as the south pole. The field lines inside the solenoid are in the form of parallel straight lines. This means the magnetic field is the same at all points inside the solenoid. This field is uniform inside the solenoid.

Fig – Field lines in solenoid

Electromagnet – A strong magnet field produced inside a solenoid can be used to magnetize a piece of magnetic material, like soft iron, when placed inside the coil. The magnet so formed is an Electromagnet.

Force on a Current-Carrying conductor in a magnetic field –

The magnetic field produced by a current-carrying conductor exerts a force on a magnet placed in the vicinity of the conductor. The French Scientist Andre Marie Ampere suggested that the magnet must also exert an equal and opposite force on the current-carrying conductor.

In the figure, AB rod experiences a force perpendicular to its length, and the magnetic field. The displacement of the rod suggests that a force is exerted on the current-carrying conductor when it is placed in the magnetic field. It is also suggested that the direction of the force is reversed when the direction of the current through the conductor is reversed. The direction of the force also reversed when the direction of the magnetic field also reversed. i.e. The direction of the force on the conductor depends upon the direction of the current and direction of the magnetic field.

The displacement of the rod is the largest when the direction of the current is perpendicular to the direction of the magnetic field.

Rule to find the Direction of Force on the conductor –

Flemings’ left-hand Rule –

Fleming’s left-hand rule is a fundamental concept in electromagnetism that helps determine the direction of force experienced by a current-carrying conductor        placed in a magnetic field.

The rule states that if you extend your left hand and orient your thumb, index finger, and middle finger mutually perpendicular to each other:

• Point your index finger in the direction of the magnetic field (B).
• Point your middle finger in the direction of the current (I) flowing through the conductor.
• Your thumb will then point in the direction of the force (F) experienced by the conductor.

Fig – Flemings’ left hand rule

Domestic Electric Circuits –

In our homes we receive supply of electric power through a main supply mains either supported through overhead electric poles or by underground cables.

Live Wire – (Red Insulation) It is a positive conductor that helps to break the circuit when excess current flows through the circuit.

Negative Wire – (black Insulation) It is a negative conductor.

The potential difference between live and neutral wire is 220 volts.

Earth wire – Earth wire is green in colour. The earth wire is connected to metal plates placed in the earth near the house for safety purposes. It provides safety for all the appliances and devices connected at home which have a metallic body. This is done to prevent shock when leakage of charges happens in the metallic body. This is done to prevent shock when leakage of charges happens in the metallic body.

Electric Fuse – From the main supply, the current is passed through the circuit called a fuse. An electric fuse is used as a safety device that protects electric circuits and appliances due to fluctuation, short-circuiting or overloading of the electric circuits. Fuse offers high resistance to voltage and has a low melting point. The fuse helps in breaking the circuit when overload current, high voltage or fluctuating current passes through the circuit. When heated, it melts and breaks the connection with the circuit, helping in preventing burning of other components/circuits. Hence, fuse is an integral part of domestic wiring as a safety device.

Electric Meter – Fuse is connected to an electric meter, an electric meter is also known as an energy meter. The earth wire from the meter is connected to ground (earthend) near the house. This meter records the electricity consumed by the house in kilowatt hour (kwh). The wires from the electric meter pass to the distribution box and are distributed to various devices when connected to the switch.

Electric circuits used for household purposes are of two types: 15 Amperes current rating circuit and 5 Amperes current rating circuit.

5 Amperes current rating circuits are used for lower power consumption sources that have lower power ratings. It includes television, fans, lights like LED and bulbs.

15 Amperes current rating circuits are used for higher power consumption sources that have a high power rating. It includes an air conditioner, geysers and iron box.