MAGNETIC EFFECTS OF ELECTRIC CURRENT
Very Short Answer Type Questions:
1. A strong bar magnet is placed vertically above a horizontal wooden board. The magnetic lines of
force will be:
(a) only in horizontal plane around the magnet
(b) only in vertical plane around the magnet
(c) in horizontal as well as in vertical planes around the magnet
(d) in all the planes around the magnet
Answer: (d) in all the planes around the magnet
2. Which of the following is not attracted by a magnet?
(a) steel
(b) cobalt
(c) brass
(d) nickel
Answer: (c) brass
3. A plotting compass is placed near the south pole of a bar magnet. The pointer of plotting
compass will:
(a) point away from the south pole (b) point parallel to the south pole
(c) point towards the south pole (d) point at right angles to the south pole
Answer: (c) point towards the south pole
4. Which of the following statements is incorrect regarding magnetic field lines?
(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a
magnetic compass needle points.
(b) Magnetic field lines are closed curves.
(c) If magnetic field lines are parallel and equidistant, they represent zero field strength.
(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines.
Answer: (c) If magnetic field lines are parallel and equidistant, they represent zero field strength.
5. Name the technique by which doctors can produce pictures showing insides of the human
body. What is the full form of MRI?
Answer: A technique called Magnetic Resonance Imaging (MRI) which is used to obtain images (or
pictures) of the internal parts of our body.
6. Assertion (A): As the speed of the coil in the motor increases, there is reduction in the current
flowing through it.
Reason (R): During rotation in electric motor, some induced current is produced.
(a) (A) is incorrect and (R) is correct.
(b) (A) is correct and (R) is incorrect.
(c) Both (A) and (R) are correct but (R) is not the correct explanation of (A).
(d) Both (A) and (R) are correct but (R) is the correct explanation of (A).
Answer: (d) Both (A) and (R) are correct but (R) is the correct explanation of (A).
Short Answer Type Questions:
, 7. When an electric current is passed through any wire, a magnetic field is produced around it.
Then why an electric iron connecting cable does not attract nearby iron objects when electric
current is switched on through it?
Answer: When an electric current is passed through a wire, it is true that a magnetic field is
produced around it. However, such magnetic fields are very weak.
The magnetic field produced by an electric iron connecting cable is very weak and is not enough to
attract nearby objects. Moreover, metallic wires of cables are shielded with a cover that prevents
magnetic field to show its effect outside the cable.
8. Fill in the following blanks with suitable words:
(a) The magnetic effect of a coil can be increased by increasing the number of..............,
increasing the ............., or inserting an..............core.
(b) If a coil is viewed from one end and the current flows in an anticlockwise direction, then this
end is a.........pole.
(c) If a coil is viewed from one end, and the current flows in a clockwise direction, then this end
is a .............pole.
(d) The two main organs of the human body where the magnetic field produced is quite
significant are the………. and the………….
Answer:
(a) Turns in the coil, current flow, soft iron.
(b) North (c) South
(d) Heart, brain
9. You are given the magnetic field pattern of a magnet. How will you find out from it where the
magnetic field is the strongest?
Answer: Magnetic field is the strongest at the place where the magnetic field lines are closest
together. 10. How is the strength of magnetic field near a straight current-conductor (i) related
to the strength of current in the conductor?
(ii) is affected by changing the direction of flow of current in the conductor?
Answer:
(i) The strength of magnetic field around a straight current conductor increases on
increasing the strength of current in the conductor or vice versa.
(ii)The direction of magnetic field around a straight current carrying conductor gets reversed
if the direction of current through that conductor is reversed.
Long Answer Type Question:
11. Define magnetic field lines. Describe an activity to draw a magnetic field line outside a bar
magnet from one pole to another pole.
Answer: The path traced by a north magnetic pole free to move under the influence of a magnetic
field is called a magnetic field line.
The bar magnet M whose magnetic field pattern is to be traced is placed on a sheet of paper and its
boundary is marked with a pencil (see Figure 7). A plotting compass is now brought near the N-pole
of the bar magnet (see position X in Figure 7). In this position, the N-pole of magnet repels the npole
of compass needle due to which the tip of the compass needle moves away from the N-pole of the
magnet. On the other hand, the N-pole of magnet attracts the s-pole of compass needle due to
Very Short Answer Type Questions:
1. A strong bar magnet is placed vertically above a horizontal wooden board. The magnetic lines of
force will be:
(a) only in horizontal plane around the magnet
(b) only in vertical plane around the magnet
(c) in horizontal as well as in vertical planes around the magnet
(d) in all the planes around the magnet
Answer: (d) in all the planes around the magnet
2. Which of the following is not attracted by a magnet?
(a) steel
(b) cobalt
(c) brass
(d) nickel
Answer: (c) brass
3. A plotting compass is placed near the south pole of a bar magnet. The pointer of plotting
compass will:
(a) point away from the south pole (b) point parallel to the south pole
(c) point towards the south pole (d) point at right angles to the south pole
Answer: (c) point towards the south pole
4. Which of the following statements is incorrect regarding magnetic field lines?
(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a
magnetic compass needle points.
(b) Magnetic field lines are closed curves.
(c) If magnetic field lines are parallel and equidistant, they represent zero field strength.
(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines.
Answer: (c) If magnetic field lines are parallel and equidistant, they represent zero field strength.
5. Name the technique by which doctors can produce pictures showing insides of the human
body. What is the full form of MRI?
Answer: A technique called Magnetic Resonance Imaging (MRI) which is used to obtain images (or
pictures) of the internal parts of our body.
6. Assertion (A): As the speed of the coil in the motor increases, there is reduction in the current
flowing through it.
Reason (R): During rotation in electric motor, some induced current is produced.
(a) (A) is incorrect and (R) is correct.
(b) (A) is correct and (R) is incorrect.
(c) Both (A) and (R) are correct but (R) is not the correct explanation of (A).
(d) Both (A) and (R) are correct but (R) is the correct explanation of (A).
Answer: (d) Both (A) and (R) are correct but (R) is the correct explanation of (A).
Short Answer Type Questions:
, 7. When an electric current is passed through any wire, a magnetic field is produced around it.
Then why an electric iron connecting cable does not attract nearby iron objects when electric
current is switched on through it?
Answer: When an electric current is passed through a wire, it is true that a magnetic field is
produced around it. However, such magnetic fields are very weak.
The magnetic field produced by an electric iron connecting cable is very weak and is not enough to
attract nearby objects. Moreover, metallic wires of cables are shielded with a cover that prevents
magnetic field to show its effect outside the cable.
8. Fill in the following blanks with suitable words:
(a) The magnetic effect of a coil can be increased by increasing the number of..............,
increasing the ............., or inserting an..............core.
(b) If a coil is viewed from one end and the current flows in an anticlockwise direction, then this
end is a.........pole.
(c) If a coil is viewed from one end, and the current flows in a clockwise direction, then this end
is a .............pole.
(d) The two main organs of the human body where the magnetic field produced is quite
significant are the………. and the………….
Answer:
(a) Turns in the coil, current flow, soft iron.
(b) North (c) South
(d) Heart, brain
9. You are given the magnetic field pattern of a magnet. How will you find out from it where the
magnetic field is the strongest?
Answer: Magnetic field is the strongest at the place where the magnetic field lines are closest
together. 10. How is the strength of magnetic field near a straight current-conductor (i) related
to the strength of current in the conductor?
(ii) is affected by changing the direction of flow of current in the conductor?
Answer:
(i) The strength of magnetic field around a straight current conductor increases on
increasing the strength of current in the conductor or vice versa.
(ii)The direction of magnetic field around a straight current carrying conductor gets reversed
if the direction of current through that conductor is reversed.
Long Answer Type Question:
11. Define magnetic field lines. Describe an activity to draw a magnetic field line outside a bar
magnet from one pole to another pole.
Answer: The path traced by a north magnetic pole free to move under the influence of a magnetic
field is called a magnetic field line.
The bar magnet M whose magnetic field pattern is to be traced is placed on a sheet of paper and its
boundary is marked with a pencil (see Figure 7). A plotting compass is now brought near the N-pole
of the bar magnet (see position X in Figure 7). In this position, the N-pole of magnet repels the npole
of compass needle due to which the tip of the compass needle moves away from the N-pole of the
magnet. On the other hand, the N-pole of magnet attracts the s-pole of compass needle due to
