MAGNETIC EFFECT OF ELECTRIC CURRENT

• The force of attraction or repulsion in and around a magnet is called magnetism.

• Magnetite or lodestone is an ore of iron – the magnet that is found in nature.

When a magnet is cutting into two parts

When a magnet is placed near a current carrying conductor

When there is no current flowing through the circuit, there is no deflection in the magnetic compass.

When current flows through the circuit, the magnetic compass deflects.

Defining a magnetic field

Region around a magnet where its force can be felt is known as the magnetic field.

Why does the iron fillings form pattern?

Due to the force exerted by the magnet, the iron filings arrange themselves in patterns as shown above.

How is a magnetic field represented ?

Magnetic field is represented by magnetic lines of forces (or) field lines.

What are magnetic field lines ?

It is the path taken by a unit North pole when placed in a magnetic field.

Magnetic field pattern due to a bar magnet

1. The field lines start from N-pole and enter into the S-pole.

2. No two lines will intersect with each other.

3. Inside the magnet the field lines move from S-N pole.

4. The magnetic lines of forces are crowded near the pole.

If you bring iron filings or iron nails close to a magnet, the filings or nails will get attracted to the magnetic poles. The centre of the magnet does not attract the filings or the nails. Why ?

Because the magnetic lines of forces are crowded near the poles.

A current carrying straight conductor produces a magnetic field – An activity

How will you find the direction of the magnetic field?

To determine the direction of the magnetic field produced in a conductor carrying

current Right Hand Thumb Rule

Right Hand Thumb Rule

When a current carrying conductor is held in the right hand,

so that the thumb is stretched along the direction of the current,

then the fingers wrapped around the conductor gives the direction of the magnetic field.

What happens when the direction of the current through the conductor is reversed?

5. What happens to the (i) number of magnetic field lines (ii) magnetic field strength When the current in the conductor increases?

Strength of the Magnetic Field

A stronger current will produce a stronger magnetic field around the wire as shown in Figure below.

Magnetic field pattern due to a circular loop carrying current

(i) Increases when the Current flowing through the coil increases.

(ii) Increases as the Number of turns of the coil increases.

(iii) decreases as the radius of the coil increases.

The magnetic field strength at the center of a circular coil carrying current

A Solenoid

An insulated copper wire wound in the form of a cylinder is called a solenoid.

A current carrying solenoid behaves as a bar magnet.

Factors affecting the magnetic field strength due to a current carrying solenoid

1. As the number of turns of the coil increases, the magnetic field strength also increases.

2. As the current flowing through the

solenoid increases , the magnetic

field strength also increases.

3. As a soft iron core is introduced in a

solenoid, the magnetic field

strength also increases.

Finding the polarity of the magnetic field produced by a current carrying solenoid

If the current flows in clockwise direction – S pole

If the current flows in anti-clockwise direction

– N Pole

• A current carrying conductor when placed in a magnetic field experiences a force and then moves.

State Fleming’s Left Hand rule .

• Stretch the thumb, the fore-finger and the centre finger of the left hand mutually perpendicular to each other,

• the forefinger in the direction of magnetic field,

• the centre finger in the direction of current , then the

• thumb will point in the direction of the force acting on the conductor.

An Electric Motor