Physics 10 Class Notes CHAPTER No 15

• Magnetic effect of steady current
• The direction of the magnetic field
• Fleming’s left-hand rule
• D.C motor
• ‘Electromagnetic induction
• Faraday’s law of electromagnetic induction
• Len’s law
• A.C Generator
• Mutual induction
• Transformer
• Relay circuit
• Solution of problems

‘Ans. Magnetism and Electromagnetism: 

“An object which attracts small pieces of iron and pointing towards north-south direction when freely suspended is known as a magnet”.

The end of a magnet pointing towards the north is called the North Pole while the end pointing towards the south is known is South pole. Properties of a Magnet:-

Following are the some important.

• A magnet attracts small pieces of iron.
• Like poles of two magnets repel while unlike poles of two magnets repel each other.
• A freely suspended magnet always points in the north-south direction.
• The magnetism of a magnet concentrated in its poles.
• The two poles of a magnet cannot be separated from each other. If a magnet is broken into two pieces, then two new magnets are obtained.
• There is a magnetic field around a magnet. A test magnet or a current-carrying conductor experiences force in a magnetic field. 

“The study of the properties associated with a magnet is called magnetism.”

Magnetism derives its name from magnesia (turkey), where it was found in the form of lumps of certain iron ore. These lumps have the property of attracting small pieces of iron. It was also known as a lodestone. 

Ans. Compass Needle: 

“A magnetized iron needle which is so pivoted that it can turn freely; in a horizontal plane is called a magnetic compass needle”. This needle comes to rest along the north-south direction.

• A compass needle is often used to investigate a magnetic field.
• It can also be used to detect current in a conductor.

“The space around a magnet in which its magnetic effect can be felt by another magnet is called the magnetic field”.

In general, any region in which magnetic effect is felt is a called magnetic field. The magnetic field is represented by the magnetic lines of force which can be traced by means of a small test magnet such as compass needle.

The intensity and direction of the magnetic field at any field point is determined by the force which the field exerts on a test magnet placed at that point.

The magnetic field of a bar magnet is represented by lines of force. The magnet field lines are directed from the North Pole to the South Pole. Electromagnetism: 

“A magnet formed due to flow of electric current in a conducting coil is called electromagnet”.

The study of the properties associated with an electromagnet is known as electromagnetism.

As we know that the electric and magnetic effects are produced by electric charge.

•  The static charge produces electrostatic effects.
•  While a moving charge that is current produces both electric and

magnetic effect (electric and magnetic fields are produced around it).

A magnetic field produced around a conductor due to flow of electric current in it is known as the magnetic field due to current.

In 182, it was Hans Oersted who first of all determined that a magnetic field is produced around a wire carrying current “I-. He also got

the following conclusion.

1. The magnetic field is strong near the conductor and becomes weaker and weaker as we move away from the conductor.
2. The magnetic field exists as long as the current is flowing through the conductor.
3. The magnetic lines of force are circular around the conductor. 

Magnetic Field of a straight current-carrying wire: 
“A magnetic field produced around a conductor due to flow of electric current in it is known as the magnetic field due to current”. 

The magnetic field due to current demonstrated by considering a straight conductor passed vertically through horizontal cardboard. The iron filings are sprinkled over the cardboard around the conducting wire.

When the switch is on and the current I allow to pass through the conductor, the iron filings arrange themselves in concentric circles around the wire in the direction of the magnetic field by taping the cad board gently. This shows that the magnetic field is produced around a current-carrying conductor. The magnetic field lines are circular around the current-carrying conductor as shown;