Selina Textbook Solutions: Electromagnetism | Physics Class 10 ICSE PDF Download

 Page 1


Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
EXERCISE 10 (A) 
 
Question 1:  
Describe an experiment to demonstrate that there is a magnetic field around a current carrying 
conductor. 
Solution 1: 
Experiment: 
In Fig , AB is a wire lying in the north- south direction and connected to a battery through a 
rheostat and a tapping key. A compass needle is placed just below the wire. It is observed that 
(1)When the key is open i.e., no current passes through the wire, the needle shows no deflection 
and it points in the N-S direction (i.e. along the earth's magnetic field). In this position, the needle 
is parallel to the wire as shown in Fig. (a). 
 
(2) When the key is pressed, a current passes in the wire in the direction from A to B (i.e.  From 
south to north) and the north pole(N) of the needle deflects towards the west [Fig. (b)]. 
 
(3) When the direction of current in the wire is reversed by reversing the connections at the 
     terminals of the battery, North Pole (N) of the needle deflects towards the east [Fig. (c)]. 
 
Page 2


Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
EXERCISE 10 (A) 
 
Question 1:  
Describe an experiment to demonstrate that there is a magnetic field around a current carrying 
conductor. 
Solution 1: 
Experiment: 
In Fig , AB is a wire lying in the north- south direction and connected to a battery through a 
rheostat and a tapping key. A compass needle is placed just below the wire. It is observed that 
(1)When the key is open i.e., no current passes through the wire, the needle shows no deflection 
and it points in the N-S direction (i.e. along the earth's magnetic field). In this position, the needle 
is parallel to the wire as shown in Fig. (a). 
 
(2) When the key is pressed, a current passes in the wire in the direction from A to B (i.e.  From 
south to north) and the north pole(N) of the needle deflects towards the west [Fig. (b)]. 
 
(3) When the direction of current in the wire is reversed by reversing the connections at the 
     terminals of the battery, North Pole (N) of the needle deflects towards the east [Fig. (c)]. 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
 
(4) If the compass needle is placed just above the wire, the North Pole (N) deflects towards 
    east when the direction of current in wire is from A to B [Fig. (d)], but the needle deflects 
    towards west as in fig (e), if the direction of current in wire is from B to A. 
 
The above observations of the experiment suggest that a current carrying wire produces a 
magnetic field around it. 
 
 
Question 2:  
Draw a diagram showing the directions of three magnetic field lines due to a straight wire 
carrying current. Also show the direction of current in the wire. 
 
Page 3


Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
EXERCISE 10 (A) 
 
Question 1:  
Describe an experiment to demonstrate that there is a magnetic field around a current carrying 
conductor. 
Solution 1: 
Experiment: 
In Fig , AB is a wire lying in the north- south direction and connected to a battery through a 
rheostat and a tapping key. A compass needle is placed just below the wire. It is observed that 
(1)When the key is open i.e., no current passes through the wire, the needle shows no deflection 
and it points in the N-S direction (i.e. along the earth's magnetic field). In this position, the needle 
is parallel to the wire as shown in Fig. (a). 
 
(2) When the key is pressed, a current passes in the wire in the direction from A to B (i.e.  From 
south to north) and the north pole(N) of the needle deflects towards the west [Fig. (b)]. 
 
(3) When the direction of current in the wire is reversed by reversing the connections at the 
     terminals of the battery, North Pole (N) of the needle deflects towards the east [Fig. (c)]. 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
 
(4) If the compass needle is placed just above the wire, the North Pole (N) deflects towards 
    east when the direction of current in wire is from A to B [Fig. (d)], but the needle deflects 
    towards west as in fig (e), if the direction of current in wire is from B to A. 
 
The above observations of the experiment suggest that a current carrying wire produces a 
magnetic field around it. 
 
 
Question 2:  
Draw a diagram showing the directions of three magnetic field lines due to a straight wire 
carrying current. Also show the direction of current in the wire. 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
Solution 2: 
 
 
Question 3:  
How is the magnetic field due to a straight current carrying wire affected if current in wire is 
(a) decreased, (b) reversed? 
Solution 3: 
(a) On decreasing the current the magnetic field lines become rarer. 
(b) The direction of magnetic field lines will get reversed. 
 
 
Question 4:  
State a law, which determines the direction of magnetic field around a current carrying wire. 
Solution 4: 
Right hand thumb rule determines the direction of magnetic field around a current carrying wire. 
It states that if we hold the current carrying conductor in right hand such that the thumb points 
in the direction of flow of current, then the fingers encircle the wire in the direction of the 
magnetic fields lines. 
 
 
Question 5:  
A straight wire lying in a horizontal plane carries a current from north to south. (a) What will 
be the direction of magnetic field at a point just underneath it? (b) Name the law used to arrive 
at the answer in part (a). 
Solution 5: 
(a) The direction of magnetic field at a point just underneath is towards east. 
(b) Right hand thumb rule. 
 
 
 
 
Page 4


Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
EXERCISE 10 (A) 
 
Question 1:  
Describe an experiment to demonstrate that there is a magnetic field around a current carrying 
conductor. 
Solution 1: 
Experiment: 
In Fig , AB is a wire lying in the north- south direction and connected to a battery through a 
rheostat and a tapping key. A compass needle is placed just below the wire. It is observed that 
(1)When the key is open i.e., no current passes through the wire, the needle shows no deflection 
and it points in the N-S direction (i.e. along the earth's magnetic field). In this position, the needle 
is parallel to the wire as shown in Fig. (a). 
 
(2) When the key is pressed, a current passes in the wire in the direction from A to B (i.e.  From 
south to north) and the north pole(N) of the needle deflects towards the west [Fig. (b)]. 
 
(3) When the direction of current in the wire is reversed by reversing the connections at the 
     terminals of the battery, North Pole (N) of the needle deflects towards the east [Fig. (c)]. 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
 
(4) If the compass needle is placed just above the wire, the North Pole (N) deflects towards 
    east when the direction of current in wire is from A to B [Fig. (d)], but the needle deflects 
    towards west as in fig (e), if the direction of current in wire is from B to A. 
 
The above observations of the experiment suggest that a current carrying wire produces a 
magnetic field around it. 
 
 
Question 2:  
Draw a diagram showing the directions of three magnetic field lines due to a straight wire 
carrying current. Also show the direction of current in the wire. 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
Solution 2: 
 
 
Question 3:  
How is the magnetic field due to a straight current carrying wire affected if current in wire is 
(a) decreased, (b) reversed? 
Solution 3: 
(a) On decreasing the current the magnetic field lines become rarer. 
(b) The direction of magnetic field lines will get reversed. 
 
 
Question 4:  
State a law, which determines the direction of magnetic field around a current carrying wire. 
Solution 4: 
Right hand thumb rule determines the direction of magnetic field around a current carrying wire. 
It states that if we hold the current carrying conductor in right hand such that the thumb points 
in the direction of flow of current, then the fingers encircle the wire in the direction of the 
magnetic fields lines. 
 
 
Question 5:  
A straight wire lying in a horizontal plane carries a current from north to south. (a) What will 
be the direction of magnetic field at a point just underneath it? (b) Name the law used to arrive 
at the answer in part (a). 
Solution 5: 
(a) The direction of magnetic field at a point just underneath is towards east. 
(b) Right hand thumb rule. 
 
 
 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
Question 6:  
What will happen to a compass needle when the compass is placed below a wire and a current 
is made to flow through the wire? Give a reason to justify your answer. 
Solution 6: 
A current carrying conductor produces a magnetic field around it and the magnetic needle in this 
magnetic field experience a torque due to which it deflects to align itself in the direction of 
magnetic field. 
 
 
Question 7:  
Draw a labelled diagram showing the three magnetic field lines of a loop carrying current. 
Mark the direction of current and the direction of magnetic field by arrows in your diagram. 
Solution 7: 
 
 
Question 8:  
A wire, bent into a circle, carries current in an anticlockwise direction. What polarity does this 
face of the coil exhibit? 
Solution 8: 
Face of the coil exhibit North polarity. 
 
 
Question 9:  
What is the direction of magnetic field at the centre of a coil carrying current in (i) clockwise, 
(ii) anticlockwise direction? 
Solution 9: 
(i) Along the axis of coil inwards. 
(ii) Along the axis of coil outwards. 
 
 
 
Page 5


Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
EXERCISE 10 (A) 
 
Question 1:  
Describe an experiment to demonstrate that there is a magnetic field around a current carrying 
conductor. 
Solution 1: 
Experiment: 
In Fig , AB is a wire lying in the north- south direction and connected to a battery through a 
rheostat and a tapping key. A compass needle is placed just below the wire. It is observed that 
(1)When the key is open i.e., no current passes through the wire, the needle shows no deflection 
and it points in the N-S direction (i.e. along the earth's magnetic field). In this position, the needle 
is parallel to the wire as shown in Fig. (a). 
 
(2) When the key is pressed, a current passes in the wire in the direction from A to B (i.e.  From 
south to north) and the north pole(N) of the needle deflects towards the west [Fig. (b)]. 
 
(3) When the direction of current in the wire is reversed by reversing the connections at the 
     terminals of the battery, North Pole (N) of the needle deflects towards the east [Fig. (c)]. 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
 
(4) If the compass needle is placed just above the wire, the North Pole (N) deflects towards 
    east when the direction of current in wire is from A to B [Fig. (d)], but the needle deflects 
    towards west as in fig (e), if the direction of current in wire is from B to A. 
 
The above observations of the experiment suggest that a current carrying wire produces a 
magnetic field around it. 
 
 
Question 2:  
Draw a diagram showing the directions of three magnetic field lines due to a straight wire 
carrying current. Also show the direction of current in the wire. 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
Solution 2: 
 
 
Question 3:  
How is the magnetic field due to a straight current carrying wire affected if current in wire is 
(a) decreased, (b) reversed? 
Solution 3: 
(a) On decreasing the current the magnetic field lines become rarer. 
(b) The direction of magnetic field lines will get reversed. 
 
 
Question 4:  
State a law, which determines the direction of magnetic field around a current carrying wire. 
Solution 4: 
Right hand thumb rule determines the direction of magnetic field around a current carrying wire. 
It states that if we hold the current carrying conductor in right hand such that the thumb points 
in the direction of flow of current, then the fingers encircle the wire in the direction of the 
magnetic fields lines. 
 
 
Question 5:  
A straight wire lying in a horizontal plane carries a current from north to south. (a) What will 
be the direction of magnetic field at a point just underneath it? (b) Name the law used to arrive 
at the answer in part (a). 
Solution 5: 
(a) The direction of magnetic field at a point just underneath is towards east. 
(b) Right hand thumb rule. 
 
 
 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
Question 6:  
What will happen to a compass needle when the compass is placed below a wire and a current 
is made to flow through the wire? Give a reason to justify your answer. 
Solution 6: 
A current carrying conductor produces a magnetic field around it and the magnetic needle in this 
magnetic field experience a torque due to which it deflects to align itself in the direction of 
magnetic field. 
 
 
Question 7:  
Draw a labelled diagram showing the three magnetic field lines of a loop carrying current. 
Mark the direction of current and the direction of magnetic field by arrows in your diagram. 
Solution 7: 
 
 
Question 8:  
A wire, bent into a circle, carries current in an anticlockwise direction. What polarity does this 
face of the coil exhibit? 
Solution 8: 
Face of the coil exhibit North polarity. 
 
 
Question 9:  
What is the direction of magnetic field at the centre of a coil carrying current in (i) clockwise, 
(ii) anticlockwise direction? 
Solution 9: 
(i) Along the axis of coil inwards. 
(ii) Along the axis of coil outwards. 
 
 
 
Class X Chapter 10 – Electro Magnetism  Physics 
_____________________________________________________________________________ 
 
Question 10:  
Draw a diagram to represent the magnetic field lines along the axis of a current carrying 
solenoid mark arrows to show the direction of current in the solenoid and the direction of 
magnetic field lines. 
Solution 10: 
 
 
Question 11:  
Name and state the rule by which polarity at the ends of a current carrying solenoid is 
determined. 
Solution 11: 
Right hand thumb rule: If we hold the current carrying conductor in right hand such that the 
thumb points in the direction of flow of current, then the fingers encircle the wire in the direction 
of the magnetic fields lines. 
 
 
Question 12:  
The adjacent diagram shows a small magnet placed near a solenoid AB. Current is switched on 
in the solenoid by pressing the key K. (a) State the polarity at the ends A and B. (b) will the 
magnet be attracted or repelled? Give a reason for your answer. 
Solution 12: 
(a) A - North pole, B - South pole. 
(b) The magnet will be repelled because the end of the solenoid near the north pole of magnet 
becomes the north pole as current at this face is anticlockwise and the two like poles repel. 
 
 
Question 13:  
The following diagram shows a spiral coil wound on a hollow carboard tube AB. A magnetic 
compass is placed close to it. Current it switched on by closing the key. (a) What will be the 
polarity at the ends A and B? (b) How will the compass needle be affected? Give reason.