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## Class Ten Science NCERT Solutions Chapter 13

#### Chapter 13: Magnetic Effects of Electric Current

Q.1. Why does a compass needle get deflected when brought near a bar magnet?

Ans. A compass needle is a small bar magnet. When it is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle shows a deflection when brought near the bar magnet.

Q.2. Draw magnetic field lines around a bar magnet.

Ans. Magnetic field lines of a bar magnet emerge from the north pole and terminate at the south pole. Inside the magnet, the field lines emerge from the south pole and terminate at the north pole, as shown in the given figure.

Q.3. List the properties of magnetic lines of force.

Ans. The properties of magnetic lines of force are as follows :

(a) Magnetic field lines emerge from the north pole.

(b) They merge at the south pole.

(c) The direction of field lines inside the magnet is from the south pole to the north pole.

(d) Magnetic lines do not intersect with each other.

Q.4. Why don’t two magnetic lines of force intersect each other?

Ans. If two field lines of a magnet intersect, then at the point of intersection, the compass needle would point in two different directions. This is not possible. Hence, two field lines do not intersect each other.

Q.5. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

Ans. Inside the loop → Pierce into the table

Outside the loop → Appear to emerge out from the table

For the clockwise direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop.

Q.6. The magnetic field in a given region is uniform. Draw a diagram to represent it. Ans. A uniform magnetic field means a number of field lines are the same in the given area, or the field lines are parallel and equispaced to each other. The diagram is given below, where the direction of the field is from the west in the east.

Q.7. Choose the correct option.

The magnetic field inside a long straight solenoid-carrying current

(a) is zero

(b) decreases as we move towards its end

(c) increases as we move towards its end

(d) is the same at all points

Ans. (d) The magnetic field inside a long, straight, current-earning solenoid is uniform. It is the same at all points inside the solenoid.

Q. 8. Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)

(a) mass

(b) speed

(c) velocity

(d) momentum

Ans. (c) and (d)

When a proton enters in a region of the magnetic field, it experiences a magnetic force. As a result of the force, the path of the proton becomes circular. Hence, its velocity and momentum change.

Q.9. In the figure, how do you think the displacement of rod AB will be affected if (i) current in rod AB is increased: (ii) a stronger horse-shoe magnet is used: and (iii) length of the rod AB is increased?

Ans. A current-carrying conductor placed in a magnetic field experiences a force. The magnitude of force increases with the amount of current, strength of the magnetic field, and the length of the conductor. Hence, the magnetic force exerted on rod AB and its deflection will increase if

(i) current in rod AB is increased

(ii) a stronger horse-shoe magnet is used

(iii) length of rod AB is increased

Q.10. A positively-charged particle (alpha-particle) projected towards the west is deflected towards the north by a magnetic field. The direction of the magnetic field is

(a) towards south

(b) towards east

(c) downward

(d) upward Ans. (d) The direction of the magnetic field can be determined by Fleming’s left-hand rule. According to this rule, if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of the magnetic field. Since the direction of a positively charged alpha particle is towards the west, the direction of the current will be the same i.e., towards the west. Again, the direction of the magnetic force is towards the north. Hence, according to Fleming’s left-hand rule, the direction of the magnetic field will be upwards.