Magnetic effect of electric
current
1. A thick copper wire XY is connected to an electric circuit.
2.A small compass needle is placed underneath
3.Note the position of the needle.
4. Current is passed through the circuit by inserting the key in the plug
5. The needle is observed
6. 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.
3. 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 1
1 A sheet of white paper is fixed on a drawing board
2 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 field
1. 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 als
o.• 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 Question
A 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
West Answer:
Below : North – South
Above : 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.
Solenoid
o 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 conductor in a magnetic field
1. A aluminium rod AB is suspended between the pole pieces of a horse shoe magnet as shown.
3. A current is allowed to flow
through the conductor AB in the direction from B to A
4. The conductor id found to get deflected to the left as shown by the arrow
5. 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.
