Magnetic effect of electric current

The term magnetic effect of electric current means that an electric current flowing in a wire produces a magnetic field around it. In other words, electric Current can produce magnetism.

Magnetic Effect of Current

The term Magnetic Effect of Electric current was coined by a Danish Physicist Hans Christian Oersted in 1820 who found that a current-carrying conductor deflects a compass needle due to the production of magnetic field lines around it.

Importance of Magnetic effect of current :-

The importance of magnetic effect of current lies in the fact that it gives rise to some mechanical forces called magnetic field lines due to which electric motor, telephone lines work.

Oersted Experiment to demonstrate the magnetic effect of Current:

Take a thin insulated copper wire such that position A of it is in the North direction. A Compass needle is also near the wire. The two ends of the wire are connected to a

battery through a key. When no Current is flowing in the wire A-B then the Compass needle remains parallel to the wire. AB and points in the Usual North-South direction.

Magnet: A magnet is any substance that attracts iron or iron-like substances.

Properties of Magnet

i) Every magnet has two poles i.e., North and South.

ii) Like poles repel each other.

(iii) Unlike poles attract each other.

(iv) A freely suspended bar magnet aligns itself in nearly north-south direction, with its Orth pole towards north direction.

Magnetic Field: The area around a magnetic in which its magnetic force can be experienced.

i) Its SI unit is Tesla (T).

ii) Magnetic field has both magnitude and direction.

iii) Magnetic field can be described with help of a magnetic compass.

iv)The needle of a magnetic compass is a freely suspended bar magnet.

Characteristics of Field Lines

i) Field lines arise from the North pole and end into the South pole of the magnet. The direction of field lines inside a magnet is from South to North.

ii) Field lines are closed curves.

iii) Field lines are closer in a stronger magnetic field.

iv)Field lines never intersect each other as for two lines to intersect, there must be two north directions at a point, which is not possible.

Right Hand Thumb Rule

Imagine you are holding a current carrying straight conductor in your right hand such that the thumb is pointing towards the direction of current. Then the fingers wrapped around the conductor give the direction of magnetic field.

Magnetic Field Lines Due To Current Carrying Conductor:

i) The magnetic field lines around a straight conductor carrying current are concentric circles whose centers lies on the wire.

ii) Direction can be given by right hand thumb rule.

iii) The magnitude of magnetic field produced by a straight current carrying wire at a point-

i) directly proportional to current passing in the wire.

ii) inversely proportional to the distance of that point from the wire.

MAGNETIC FIELD DUE TO A CURRENT THROUGH A CIRCULAR LOOP

i) The magnetic field lines are circular near the current carrying loop. As we move away, the concentric circles become bigger and bigger. At the centre, the lines are straight.

ii)At the centre, all the magnetic field lines are in the same direction due to which the strength of magnetic field increase.

iii)The magnetic of magnetic field produced by a current carrying circular loop at its centre is

i) directly proportional to the current passing

ii) inversely proportional to the radius of the circular loop

iv) The strength of magnetic field produced by a circular coil carrying current is directly proportional to both number of turns(n) and current(I) but inversely proportional to its radius(r).

his magnet can be easily understood with the help of the Clock Face Rule.

i) If the current is flowing in anti–clockwise direction, then the face of the loop shows north pole.

ii) On the other hand, if the current is flowing in clockwise direction, then the face of the loop shows south pole.

MAGNETIC FIELD DUE TO A CURRENT IN A SOLENOID

The insulated copper wire wound on a cylindrical tube such that its length is greater than its diameter is called a solenoid.

i) The magnetic field produced by a current-carrying solenoid is similar to the magnetic field produced by a bar magnet.

ii) One end of solenoid behaves as the north pole and another end behaves as the south pole.

iii) Direction of magnetic field: Outside the solenoid: North to South, inside the solenoid: South to North.

iv) Magnetic field is uniform inside the solenoid and represented by parallel field lines.

v) The current in each turn of a current carrying solenoid flows in the same direction due to which the magnetic field produced by each turn of the solenoid ads up, giving a strong magnetic field inside the solenoid .

The strength of the magnetic field at the centre of the loop(coil) depends on :

(i) The radius of the coil: The strength of the magnetic field is inversely proportional to the radius of the coil. If the radius increases, the magnetic strength at the centre decreases.

(ii) The number of turns in the coil : As the number of turns in the coil increase, the magnetic strength at the centre increases, because the current in each circular turn is having the same direction, thus, the field due to each turn adds up.

(iii) The strength of the current flowing in the coil: As the strength of the current increases, the strength of three magnetic fields also increases.

ELECTROMAGNETS AND PERMANENT MAGNETS

An electromagnet is a temporary strong magnet and is just a solenoid with its winding on a soft iron core.

A permanent magnet is made from steel. As steel has more retentivity than iron, it does not lose its magnetism easily.

Difference between Electromagnet and permanent magnet

Electromagnet

Permanent magnet

1. An electromagnet is a temporary magnet as it can readily be demagnetized by stopping the current through the solenoid.

2. Strength can be changed.

3. It produces very strong magnetic forces.

4. Polarity can be changed by changing the direction of the current.

1. A permanent magnet cannot be readily demagnetized.

2. Strength cannot be changed.

3. It produces weak forces of attraction.

4. Polarity is fixed and cannot be changed.

FORCE ON A CURRENT-CARRYING CONDUCTOR IN A

MAGNETIC FIELD

1) A current-carrying conductor exerts a force when a magnet is placed

in its vicinity. Similarly, a magnet also exerts equal and opposite force

on the current carrying conductor. This was suggested by Marie

Ampere, a French Physicist and considered as founder of science of

electromagnetism.

2) The direction of force over the conductor gets reversed with the

change in direction of flow of electric current.

3)It is observed that the magnitude of force is highest when the

direction of current is at right angles to the magnetic field.

Fleming’s Left Hand Rule

Stretch the thumb, fore finger and middle finger of your left hand
such that they are mutually perpendicular. If fore finger points in
the direction of magnetic field, middle finger in the direction of
current then thumb will point in the direction of motion or force.

Electro Magnetic Induction

When a conductor is placed in a changing magnetic field, some current

is induced in it. Such current is called induced current and the

phenomenon is called electromagnetic induction.

Direct Current: The unidirectional flow of an electric charge is

referred to as direct current. Current flows in one direction only.

Alternate Current (A.C ): Current in which direction is changed periodically is called alternate Current. The direction of current changes after every 1/100 second in India, i.e. the frequency of A.C in India is 50 Hz.

Alternating Current (AC)	Direct Current (DC)
The flow of electric current is constantly changing.	The electric current flows in one direction.
The voltage is not steady	Voltage is steady
It can be transferred over long distances	It cannot be transferred over long distances
Less loss of energy	more loss of energy
For India the frequency of AC is 50 Hz	The frequency of DC is zero
It can not be stored.	It can be stored.
Source of availability is AC generators	Source of availability is battery, electrochemical cells, or storage devices

Domestic Electric Circuits: In our houses, we receive AC
electric power of 220 V with a frequency of 50 Hz.
Either underground cables or overhead wires are used to supply
electricity to a home. Three distinct insulated wires make up the cable:
1) Live wire – Live wire is red in colour. It is a positive conductor that

helps to break the circuit when excess current flows through the circuit.

2)Neutral wire - Neutral wire is black in colour. It is a negative

conductor.

3)Earth wire - Earth wire is green in colour. 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.

Short Circuit: Short-circuit happens when the neutral wire comes in

contact with the live wire. It happens when wires of low resistance are

used or when the insulation of the wire is damaged and one wire gets in

contact with another.

Overloading of an Electric Circuit: If too many electrical appliances

are used simultaneously or too many electrical appliances are

connected to the same socket they draw extremely large current from

the circuit. Due to this, the wire may get overheated, and fire may start.

This is called overloading.

Electric Fuse: It is a protective device used for protecting the circuit from short-circuiting and overloading. It is a piece of thin wire of material having a low melting point and high resistance.

Fuse is always connected to live wire.
Fuse is always connected in series to the electric circuit.

Fuse is always connected to the beginning of an electric circuit.

Fuse works on the heating effect.

Science

Wednesday, October 18, 2023