Magnetic effect of electric current

1. A thick copper wire XY is connected to an electric circuit.

2.A small compass needle is placed underneath3.Note the position of the needle.4. Current is passed through the circuit by inserting the key in the plug5. The needle is observed6. The compass needle gets deflected.7. WHY SHOULD IT GET DEFLECTED?

1. A mag. Needle gets deflected in presence of a magnet, due to the influence of mag. Field of bar magnet.

2. Therefore the deflection of mag. needle kept under the current carrying wire is due to the mag. field produced by the wire.

3. Thus electricity and magnetism are linked to each other.

A compass needle is a small bar Magnet. A freely pivoted magnetic needle always point

approximately towards north- south direction. (DIRECTIONAL PROPERTY)The end pointing towards north is called north

seeking or north pole.The end pointing towards south is called south

seeking or south pole.

Recapitulation - Magnetism

OTHER PROPERTIES

• Unlike poles Attract

• and like poles repel

• POLES EXIST IN PAIRS• (MONO POLES DOES NOT EXIST)

Activity 11 A sheet of white paper is fixed on a

drawing board2 A bar magnet is kept in the centre and

iron filings are uniformly sprinkled around the bar magnet

3 The board is tapped gently.4 The iron filings arrange themselves in a

pattern as shown.5 This represents the magnetic field

around the magnet.6 The iron filings arrange them selves due

to the force exerted by the bar magnet.7 The field can be plotted using a

compass needle also.

The region surrounding a magnet , in which the force of magnet can be detected is said to have a magnetic field.Magnetic field is a quantity that has both magnitude and direction.

The curved lines along which the iron filings align themselves or the path along which the freely pivoted magnetic needle moves is called the field lines or magnetic lines of force.

The direction of the field is taken to be the direction in which a north pole of the compass needle moves inside it.

Characteristics of magnetic field1. Strength of magnetic field is a quantity that can be expressed both in magnitude and direction.2. The relative strength of a magnetic field is shown by the degree of closeness of magnetic field lines; (i.e. greater the number of magnetic field lines in a unit space, more is the strength of magnetic field)3. The strength of magnetic field at a given point depends upon its distance of from the poles of a bar magnet. (i.e. more the distance, less is the strength of magnetic field.)

Characteristics of magnetic field line.

• 1. A magnetic field line can be defined as the path along which a free north pole will move in a magnetic field.

• 2. Magnetic field lines are closed curves.• 3. Magnetic field lines appear to start from N-pole and appear

to end at the south pole. (within the magnet , they run from S- pole to N- north pole) 4. Magnetic field lines repel each other. 5. No two magnetic lines cut each other. ( If they intersect , a

compass needle placed at the intersection has to point two different directions at the same time which is impossible.)

Magnetic field around a current carrying wire

Right-hand Thumb Rule• When you wrap

your right hand around the straight conductor such that the thumb points in the direction of the current, the fingers will wrap around the conductor in the direction of the field lines of the magnetic field..

Right Hand Thumb Rule

Magnetic field due to current through a straight conductor.

The current through a wire produces a magnetic field.

The shape of the magnetic field lines for a straight conductor is concentric circles.

These concentric circles become larger as we move away from the wire.

Magnetic field due to current in a straight long conductor

1. Take a thick copper wire and pass it through a horizontal card board as shown.

2. Pass a strong current through the wire.

3. Sprinkle iron filings on the cardboard around the wire.

4. Tap the cardboard gently. You would see a pattern as shown here.

5. You may plot the field lines with a compass needle also.

• 1. The magnetic field lines are in the form of concentric circles near the conductor

2.Away from the conductor the field lines tend to be elliptical due to the combined effect of earth magnet and mag. Field due to the conductor.

3.The direction of magnetic field lines reverses with the reversal of the direction of current in the conductor.

4.Increasing the strength of the current in the conductor results in increase in mag. Field lines .

that is intensity of magnetic field increases with the increase in strength of the current. (No of magnetic field lines around the conductor increases)5. The magnetic field at a point decreases with the increase in distance from the conductor.

Review QuestionA current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?

East

North south

WestAnswer:Below : North – SouthAbove : South to North

Magnetic field due to current in a circular loop

Properties of magnetic field lines 1. The magnetic field lines are near

circular at the points where the current enters or leaves the card board

2. Within the space enclosed by the coil, the field lines are in same direction.

3. Near the centre of the coil, the magnetic lines are almost parallel to each other. Thus mag. Field near the centre of the coil may be considered uniform.

4. At the centre of the coil the plane of magnetic field lines is at right angle to the plane of the coil.

5. If there is a circular coil having n turns, the field produced is n times as large as that produced by a single turn ,as the current in each turn has the same direction and the field due to each turn add up.

Solenoido A coil of many circular turns of

insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.

o A solenoid produces a magnetic field when electric current is passed through it.

o The pattern of the magnetic field lines around a current-carrying solenoid is similar to that of a bar magnet.

o One end of the solenoid is like a magnetic north pole while the other is like the south pole

MAGNETIC FIELD PRODUCED BY A SOLENOID

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

Force on current carrying conductorin a magnetic field

1. A aluminium rod AB is suspended between the pole pieces of a horse shoe magnet as shown.

2. A current is allowed to flow through the conductor AB in the direction from B to A

3. The conductor id found to get deflected to the left as shown by the arrow

4. When the poles of the magnet is interchanged and when the current is still from B to A, the force on the conductor is found to be on the right as shown.

5.If the current is from A to B( Direction is reversed) without reversing the pole pieces of the magnet. The deflection of the conductor(force) is to the left as shown.

6. If the current is from A to B( Direction is reversed) reversing the pole pieces of the magnet. The deflection of the conductor(force) is to the right as shown.

Force on a current-carrying conductor in a magnetic field

• An electric current flowing through a conductor produces a magnetic field. The field so produced exerts a force on a magnet placed in the vicinity of the conductor.

• The magnet also exerts an equal and opposite force on the conductor.

• The magnitude of this force is highest when the direction of current is at right angles to the direction of the magnetic field.

• To Sum up

• The direction of force is reversed when the direction of current through the conductor is reversed.

• The direction of force is also reversed by interchanging the two poles of the magnet.

Fleming’s left-hand rule• The directions of the current, force, and

magnetic field can be illustrated through a simple rule called Fleming’s left-hand rule, if the direction of current is at right angles to the direction of the magnetic field.

• According to this rule, stretch the thumb, forefinger, and middle finger of your left hand such that they are mutually perpendicular.

• The first finger points in the direction of the magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.