Question 1

Question 1Write true or false for each statement:(a) A current carrying coil when suspended freely can rest in any direction.(b) A coil carrying current behaves like a magnet.(c) In an electromagnet, the core is made up of copper.(d) An electric bell uses an electromagnet.(e) An electromagnet with soft iron core is a temporary magnet.(f) We use cell as the source of electricity to run an electric immersion rod.(g) A torch bulb glows if the terminals of the bulb are connected to the terminals of a cell by the metallic wire.(h) Wool is a conductor of electricity.(i) Silver is an insulator of electricity.(j) Our body is a conductor of electricity.(k) For a circuit to be complete, every part of it must be made up of conductors.(l) All metals are conductors of electricity.(m) The switch should not be touched with wet hands.(n) A switch is an on-off device in an electric circuit.

Accepted Answer

(a) FalseCorrect Statement — A current carrying coil when suspended freely rest in north-south direction.(b) True(c) FalseCorrect Statement — In an electromagnet, the core is made up of soft iron.(d) True(e) True(f) FalseCorrect Statement — We do not use cell as the source of electricity to run an electric immersion rod.(g) True(h) FalseCorrect Statement — Wool is an insulator of electricity.(i) FalseCorrect Statement — Silver is a conductor of electricity.(j) True(k) True(l) True(m) True(n) True

Question 2

Question 3Match the following:Column AColumn B(a) Human body(i) electric bell(b) Silk thread(ii) current(c) Charge in motion(iii) conductor(d) Soft iron(iv) electromagnet(e) Electromagnet(v) insulator

Accepted Answer

Column AColumn B(a) Human body(iii) conductor(b) Silk thread(v) insulator(c) Charge in motion(ii) current(d) Soft iron(iv) electromagnet(e) Electromagnet(i) electric bell

Question 3

Question 4bElectromagnets are made up of:steelcopperbrasssoft iron

Accepted Answer

soft ironReason — Electromagnets are temporary magnets made up of soft iron because they can easily be magnetized on passing electric current and gets de-magnetized when flow of electric current is stopped.

Question 4

Question 4hWe should not touch the switch with wet hands, otherwise:electricity may pass through our bodyelectricity may not pass through the appliancecircuit may breakthe switch may get off

Accepted Answer

electricity may pass through our bodyReason — We should not touch the switch with wet hands as tap water conducts electricity. Electricity will pass through our body and we can get electric shock.

Question 5

Question 2How will you test whether a given rod is a magnet or not?

Accepted Answer

Suspend the given rod such that it swings freely and note the direction in which the rod rests. Repeat the process two to three times. If the rod rests in a particular direction pointing north and south in each case then the rod is a magnet. But if it rests in any random direction, then it is not a magnet.

Question 6

Question 4You are given two similar bars. One is a magnet and the other is of soft iron. How will you distinguish and identify them?

Accepted Answer

Let the two identical bars be bar A and bar B.Take the bar A and place it on a table.Take the bar B and touch it to one end of bar A, then at another end and then in middle. If the bar B sticks to the bar A at both the ends and also at the middle, then the bar A is made up of soft iron.Repeat the above process by placing the bar B on the table and touch the bar A on one end, then on another end and finally on middle of bar B. We will find that the bar A will be attracted towards both the ends of bar B, but not to the middle which shows that bar B is a magnet.

Question 7

Question 6Describe a simple experiment to illustrate that like poles of two magnets repel each other while unlike poles attract.

Accepted Answer

Take two bar magnets A and B.Suspend one magnet A with a silk thread from a support so that it is free to swing.The magnet A will come to rest in the north-south direction. The north pole of the magnet A is in north direction and its south pole is in the south direction.Now hold the other magnet B in your hand and bring its north pole near the north pole of the suspended magnet A without touching the magnet.We will observe that two poles repel each other.Now bring the south pole of the magnet B near the north pole of the suspended magnet A without touching it.We will observe that the two poles attract each other.The above experiment shows that like poles repel and unlike poles attract each other.

Question 8

Question 7"Poles exist in pairs". Comment on this statement.

Accepted Answer

If a bar magnet is broken at the middle in two parts, each part is found to be a magnet. Each part has the property to attract small iron pieces. Each part when suspended freely, rests in north-south direction. This shows that new poles are formed at each broken parts. If these parts are broken again and again, still each part will be a complete magnet with north and south poles. This shows that poles exists in pairs.

Question 9

Question 8What is a magnetic compass? State its use.

Accepted Answer

A magnetic compass is a small magnetic needle pivoted at the centre of a small brass box which has a glass top. It is used to locate directions at a place.

Question 10

Question 9Explain the meaning of the term magnetic field.

Accepted Answer

The space around a magnet in which the magnetic needle of the magnetic compass gets influenced is called its magnetic field.

Question 11

Question 10What is an electromagnet?

Accepted Answer

An electromagnet is a temporary magnet made by winding wire around a soft iron core and on passing electric current it creates a magnetic field around itself and behaves like a magnet.

Question 12

Question 12Draw a labelled diagram to make a soft iron bar as an electromagnet. Describe in steps the procedure.

Accepted Answer

Take a soft iron bar PQ and wind a thin insulated copper wire around the bar.Connect a cell or a battery and a key K in series between the ends of a coil as shown in the below figure.When key is closed current passes through the winding of the coil and the bar becomes a magnet.But when key is opened the current stops flowing in the coil and bar gets demagnetized.So, soft iron bar behaves as an electromagnet when current passes through the coil.

Question 13

Question 13You are given a U-shaped soft iron piece, insulated copper wire and a battery. Draw a circuit diagram to make a horse shoe electromagnet.

Accepted Answer

Circuit diagram to make a horse shoe electromagnet is given below:

Question 14

Question 14Name two factors on which the strength of magnetic field of an electromagnet depends.

Accepted Answer

The two factors on which the strength of magnetic field of an electromagnet depends are:Number of turns of the coil.Strength of current passing through the coil.

Question 15

Question 15State two ways by which the strength of magnetic field of an electromagnet can be increased.

Accepted Answer

The two ways by which the strength of magnetic field of an electromagnet can be increased are:By increasing the total number of turns of the coil.By increasing the strength of current passing through the coil.

Question 16

Question 16State two common uses of electromagnets.

Accepted Answer

The two common uses of electromagnets are:For loading furnaces with iron.It is used in electrical gadgets like electric bell, electric tram, microphone, loudspeaker, electric motor etc.

Question 17

Question 17Name a domestic device in which an electromagnet is used.

Accepted Answer

Electric bell

Question 18

Question 18Draw a neat and labelled diagram of an electric bell and describe its working.

Accepted Answer

Labelled diagram of the electric bell is shown below:Working of electric bell:When the switch (bell push) is pressed, current flows through the coil of electromagnet.The electromagnet gets magnetized and attracts the armature. As the armature moves the hammer attached to it moves and strikes the gong so the bell rings.During this process the contact between the metallic springy strip and adjusting screw breaks so the circuit becomes incomplete.The current stops flowing through the coil of electromagnet and it gets demagnetized.As the electromagnet gets demagnetized, the armature comes back to its original position due to spring action of the metallic springy strip and comes in contact with the adjusting screw.The circuit becomes complete, if the bell push is pressed again, current will flows through the coils of electromagnet and it gets magnetized.It attracts the armature and hammer attached with it strikes the gong again and the bell rings.This process of making and breaking the circuit continues and the bell rings as long as the bell push remains pressed.

Question 19

Question 19The incomplete diagram of an electric bell is given in figure below. Complete the diagram and label its different parts.

Accepted Answer

The complete and labelled diagram of the electric bell is shown below:

Question 20

Question 20What is declination? Draw a diagram to show the angle between the declination and true direction of geographic north.

Accepted Answer

Magnetic declination is the angle of the horizontal plane between the magnetic north and the geographic north (or true north).

Electricity and Magnetism

Objective Questions

Short/Long Answer Questions