# Samacheer Kalvi Class 8 Science Unit 7 Magnetism Solutions

## Samacheer Kalvi Class 8 Science Unit 7 Magnetism Solutions

Welcome to NCTB Solutions. Here with this post we are going to help 8th class students by providing Solutions for Samacheer Kalvi Class 8 Science Unit 7 Magnetism. Here students can easily find all the solved solution for Magnetism Exercise questions. Also here our Expert Science Teacher’s solved all the questions with easily understandable language with proper guidance so that all the students can understand easily. Here on this post students will get Unit 7 Magnetism exercise solutions. Here all the solutions are based on Tamil Nadu State Board latest syllabus.

#### Unit 7 Magnetism Exercise Questions Solutions :

(I) Choose the best answer

(1) A magnet attracts ____

(a) Wooden materials

(b) Any metal

(c) Copper

(d) Iron and steel

Correct Option → (d)

A magnet attracts Iron and steel.

(2) One of the following is an example for a permanent magnet

(a) Electromagnet

(b) Mu-metal

(c) Soft iron

(d) Neodymium

Correct Option → (d)

Neodymium is an example for a permanent magnet.

(3) The south pole of a bar magnet and the north pole of the a U shaped magnet will

(a) Attract each other

(b) Repel each other

(c) Neighter attract nor repel each other

(d) None of the above.

Correct Option → (a)

The south pole of a bar magnet and the north pole of the a U shaped magnet will Attract each other.

(4) The shape of the Earth’s magnetic field resembles that of an imaginary ___

(a) U-shaped magnet

(b) straight conductor carrying current

(c) solenoid coil

(d) bar magnet

Correct Option → (d)

The shape of the Earth’s magnetic field resembles that of an imaginary Bar magnet.

(5) MRI stands for ____

(a) Magnetic resonance imagine

(b) Magnetic ruunig image

(c) Magnetic radio imaging

(d) Magnetic radar imaging

Correct Option → (a)

MRI stands for Magnetic resonance imagine.

(6) A compass is used for ____

(a) Plotting magnetic lines

(b) Detection of magnetic field

(d) All of these

Correct Option → (d)

A compass is used for all of the above situations.

(II) Fill in the blanks

(1) The magnetic strength is ___ at the poles.

(2) A magnet has ___ magnetic poles.

(3) Magnets are used in ___ for generating electricity.

(4) ___ are used to lift heavy iron pieces.

(5) A freely suspended bar magnet is always pointing along the ___ north-south direction.

(1) → strongest

(2) → north-south

(3) → magnetic fields

(4) → Electromagnets

(5) → geographic

(1) Define magnetic field.

The space around the bar magnet where the arrangements of iron fillings exists represent the field of influence of the bar magnet is known as magnetic field. Or It is defined as the space around a magnet in which its magnetic effect or influence is observed is known as the magnetic field.

(2) What is artificial magnet? Give examples.

Artificial magnet : Magnets are made by people in the laboratory or factory are called artificial magnet or man made magnets. For e .g – the magnet made up of iron, nickel ,cobalt, etc. Neodymium and samarium known as artificial magnet.

(3) Distinguish between natural and artificial magnets?

Natural magnet :

• Magnets found in the nature are called natural magnet.
• This magnet are permanent magnet they do not lose their magnetic power.
• For e.g – lodestone, Columbine etc.

Artificial magnet :

• The magnets are made in the laboratory or factory are called artificial magnet.
• Artificial magnet can be made in different shapes like bar magnets, u shaped magnets, horse shape etc.
• For e.g – neodymium, magnets of iron, nickel , cobalt etc.

(4) Earth acts as a huge bar magnet. Why? Give reasons.

A freely suspended magnetic needle at a point on the earths comes to rest approximately along the geographical north-south direction it is shows that earth acts as a huge magnetic dipole with its magnetic poles located near its geographical poles, and therefore it acts like a huge bar magnet.

(5) How can you identify non-magnetic materials? Give an example of a non-magnetic material.

The materials which are attracted by magnets are called magnetic materials and the materials which are not attracted by magnets are called non- magnetic material. Examples of non–magnetic materials are rubber, leather materials, wood, plastic, etc.

(VI) Answer in detail

(1) List out the uses of magnets.

Following are the used of magnets :

• Magnets are used to generate electricity in dynamos.
• Magnets are used in electrical bells and electrical motors
• Magnets are also used in loudspeakers and microphones.
• They are also used as an extremely powerful electromagnet in fast moving Maglev train to remain floating above the tracks.
• In industries, magnetic conveyor belts are used to sort out magnetic substances from scraps mixed with non- magnetic substances.
• Magnets are used in computer in its storing devices such as hard disks.

(2) How will you convert a ‘nail’ into a temporary magnet?

Temporary magnets are produced with the help of an external magnetic field. They lose their magnetic property as soon as the external magnetic field is removed.

For example consider spread a steel pins on a wooden board and bring an iron nail near them, now make one magnetic poles of the bar magnet touch one end of the iron nail slide it along its length in one direction slowly till the outer end is reached. Do it 20 times the magnet moved in one direction only and now bring the iron nail near the steel pins. The steel pins stick to the iron nail because nail has become a temporary magnet this is the way to make convert a nail into a temporary magnet.

(3) Write a note on Earth’s magnetism.

Earth’s magnetism : Earth is known as huge magnetic dipole, the earth is located near the geographic north pole and the north pole of the earths magnet is located near the geographic south pole. The line joining these pole is called the magnetic axis. Similarly the geographic north pole at a point called the north geomagnetic pole or northern magnetic pole. The exact cause of the Earth’s magnetism is not known even today. However some important factors which may be the cause of the Earth’s magnetism are as follows –

• Masses of magnetic substances in the earth
• Radiation from the sun
• Action of the moon

The earth magnetic field is believed that the earth’s magnetic field is due to the molten charged metallic fluid inside the earth’s surface with a core of radius of about 3500 km compared to the earth’s radius of 6400 km.

(VII) Higher Order Thinking Questions.

(3) Thamizh Dharaga and Sangamithirai were playing with a bar magnet. They put the magnet down and it broke into four pieces. How many poles will be there?