Intext Questions (within section 12.1)
Q1. Why does a compass needle get deflected when brought near a bar magnet?
Answer:
A compass needle is a small bar magnet. When brought near a bar magnet, the magnetic field of the bar magnet exerts a force on the compass needle, causing it to align with the field lines. The unlike poles attract, and like poles repel, leading to the deflection of the needle.
Intext Questions (within section 12.2)
Q1. Draw magnetic field lines around a bar magnet.
Answer:
Magnetic field lines emerge from the north pole of a bar magnet and merge at its south pole. Inside the magnet, the direction of field lines is from the south pole to the north pole, forming closed curves. The lines are crowded near the poles, indicating a stronger magnetic field.
Q2. List the properties of magnetic field lines.
Answer:
Properties of magnetic field lines are:
1. They emerge from the north pole and merge at the south pole (outside the magnet).
2. Inside the magnet, they go from the south pole to the north pole, forming closed curves.
3. The closeness of field lines indicates the strength of the magnetic field — crowded lines mean a stronger field.
4. No two field lines intersect each other.
Q3. Why don’t two magnetic field lines intersect each other?
Answer:
If two magnetic field lines intersected, at the point of intersection the compass needle would point in two different directions simultaneously, which is not possible. Therefore, magnetic field lines never intersect each other.
Intext Questions (within section 12.2)
Q1. 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.
Answer:
Using the right-hand thumb rule: if the current is clockwise in the loop lying on the table, curl the fingers of your right hand in the direction of the current (clockwise). Your thumb points downward. Therefore, the magnetic field inside the loop is directed into the table (downward). Outside the loop, the magnetic field lines emerge upward (out of the table) to form closed loops.
Q2. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer:
A uniform magnetic field is represented by parallel, equally spaced straight lines (arrows) pointing in the same direction. For example, inside a current-carrying solenoid, the field lines are parallel and equally spaced, indicating that the field strength and direction are the same at all points in that region.
Q3. 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.
Answer:
The correct option is (d) is the same at all points.
Explanation: Inside a long straight current-carrying solenoid, the magnetic field lines are parallel and equally spaced, which indicates a uniform magnetic field. Hence, the field strength is the same at all points inside the solenoid.
Example
QExample 12.1. A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?
Answer:
The current is in the east-west direction. Applying the right-hand thumb rule, we get that the magnetic field (at any point below or above the wire) turns clockwise in a plane perpendicular to the wire, when viewed from the east end, and anti-clockwise, when viewed from the west end.