CBSE Class 10 Physics Magnetic Effects of Electric Current Previous Year Questions

A freely suspended current-carrying solenoid cannot stay in any direction. It will always tend to align itself along the direction of the magnetic field it produces, due to the interaction of the solenoid’s magnetic field with the Earth’s magnetic field — just like a bar magnet aligns in the north-south direction.

Reversal of Current in the Solenoid:
When the direction of current in the solenoid is reversed, the polarity of the magnetic field it generates also reverses. This reversal causes the solenoid to experience a torque in the opposite direction, which tries to re-align it with the reversed field. As a result, the solenoid flips its orientation to minimise the torque and aligns itself in the new direction dictated by the reversed current.

Definition: A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. It creates a uniform magnetic field when an electric current passes through it.

Magnetic Field Lines Through and Around a Current-Carrying Solenoid:
The magnetic field inside the solenoid is uniform and parallel to its axis. The magnetic field lines outside form closed loops travelling from one end to the other. Inside, field lines are parallel and equally spaced, indicating a strong uniform field.


Inside the solenoid, field lines run parallel and uniformly along its length. Outside, they emerge from one end, curve around, and enter the other end — forming closed loops similar to a bar magnet.

Magnetic field lines are imaginary continuous closed curves used to represent the magnetic field in a region. They move from the north pole to the south pole outside the magnet, and from the south pole to the north pole inside the magnet.

(a) Two magnetic field lines never intersect each other because at the point of intersection, the magnetic field would have two directions simultaneously, which is physically impossible. The field at any point can have only one direction.

(b) Magnetic field lines are closed curves because they always form complete loops — the field inside the magnet travels from the south pole to the north pole, continuing the circular path that exists outside the magnet from north to south.

(a) Increase in current: The deflection of the compass needle increases.
Reason: The strength of the magnetic field is directly proportional to the magnitude of current passing through the conductor. A stronger current produces a stronger magnetic field, causing greater deflection of the needle.

(b) Compass needle displaced away: The deflection of the compass needle decreases.
Reason: The magnetic field strength is inversely proportional to the distance from the conductor. As the compass needle moves farther away, the magnetic field it experiences weakens, causing less deflection.

Yes, there will be an induced current in both cases. The key factor is the relative motion between the magnet and the coil — what matters is that there is a change in the number of magnetic field lines associated with the coil (change in magnetic flux). Whether the magnet moves towards the coil or the coil moves towards the magnet, the relative motion is the same.

The same magnitude of current will be induced, and the direction of flow of induced current will also be the same in both cases.

(i) The convergence or divergence of magnetic field lines near the ends of a current-carrying solenoid occurs because the solenoid behaves like a bar magnet, and its ends act like the poles of a magnet. Near the poles, field lines converge or diverge just as they do near the poles of a bar magnet.

(ii) When a current-carrying solenoid is suspended freely, it behaves like a magnet and aligns itself along the north-south direction due to the Earth’s magnetic field, in the same way that a freely suspended bar magnet comes to rest in the north-south direction.

The device used to draw magnetic field lines around a bar magnet is a compass needle.

Magnetic field lines are drawn from the north pole to the south pole outside the magnet, and from the south pole to the north pole inside the magnet, forming continuous closed loops.

The magnetic field is a physical quantity that possesses both direction and magnitude.

Direction: The direction of the magnetic field is taken to be the direction in which the north pole of a compass needle moves inside the magnetic field. By convention, magnetic field lines emerge from the north pole and merge at the south pole of a magnet. Inside the magnet, the direction of field lines is from the south pole to the north pole.

Magnitude: The magnitude of the magnetic field is represented by the density of the field lines. The stronger the magnetic field, the closer the field lines are to each other. Where field lines are crowded, the field strength is stronger; where they are spread out, the field is weaker.

(a) Magnitude of electric current in wire is increased:
Observation: The compass needle deflects more as the current increases.
Reason: A stronger electric current creates a stronger magnetic field around the wire, which causes an increased deflection of the compass needle. The magnetic field around the wire is directly proportional to the magnitude of the current flowing through it.

(b) The compass needle is displaced away from the wire:
Observation: The deflection of the compass needle decreases as it is moved farther from the wire.
Reason: The strength of the magnetic field is inversely proportional to the distance from the conductor. As the compass needle is displaced farther away, it experiences a weaker magnetic field, causing less deflection.

(a) Iron filings align themselves along the magnetic field lines produced by the bar magnet. The magnetic field exerts a force on the iron filings, causing them to orient themselves along the direction of the field. The pattern formed visually represents the shape and direction of the magnetic field.

(b) The pattern of magnetic field lines indicates the strength and direction of the magnetic field. The density of lines represents strength (closer lines indicate a stronger field), while the direction of the lines shows the direction of the field at different points.

(c) Two properties of magnetic field lines:
1. Closed loops: Magnetic field lines form closed loops and do not have any starting or ending points.
2. Non-intersecting: Magnetic field lines never intersect each other. If they did, it would imply that the magnetic field has more than one direction at a point, which is impossible.

(a) The rod is displaced towards the left. This is because a force is exerted on the current-carrying aluminium rod when placed in a magnetic field. According to Fleming’s Left-Hand Rule, the direction of force is perpendicular to both the magnetic field and the current. The rod experiences a force causing it to move in the direction determined by the rule.

(b) No displacement will be observed. This is because the angle between the magnetic field and the current in the rod is zero (they are parallel). When the current is aligned parallel to the magnetic field, the force on the conductor becomes zero, as the magnetic force requires a component of the current to be perpendicular to the field.

(i) Maximum: The force experienced by a current-carrying straight conductor placed in a uniform magnetic field is maximum when the conductor is perpendicular to the direction of the magnetic field. At 90°, the entire current contributes to the force.

(ii) Minimum: The force experienced by a current-carrying straight conductor is minimum (zero) when the conductor is parallel or anti-parallel to the direction of the magnetic field, since there is no component of current perpendicular to the field.

Figure ‘a’: The magnetic field lines are directed from P to Q, so:
 • P is the North pole
 • Q is the South pole

Figure ‘b’: The magnetic field lines are directed from R to S, so:
 • R is the North pole
 • S is the South pole

(b) Inference: In the given diagrams, magnetic field lines outside the magnet go from the North pole to the South pole. This indicates that magnetic field lines always emerge from the North pole and enter the South pole of a magnet. The field lines are closed loops, continuing inside the magnet from the South pole to the North pole.

A compass needle shows deflection when brought near a current-carrying conductor because the conductor produces a magnetic field around it when current flows through it. This magnetic field interacts with the magnetic needle of the compass, exerting a force on it and causing it to deflect from its original north-south alignment. The greater the current or the closer the needle, the larger the deflection.

Magnetic field lines are more crowded towards the poles of a magnet because the magnetic field is strongest near the poles. Due to the formation of closed magnetic loops, a greater number of magnetic field lines pass through the region near the poles, making them appear more crowded. The density of field lines at any point is a measure of the strength of the magnetic field — closer lines indicate a stronger field, and the field is strongest at the poles.

(a) Electromagnet: An electromagnet is a current-carrying solenoid. When soft iron is placed inside a solenoid carrying current, the soft iron behaves like a magnet as long as the electric current passes through it. The magnet formed is called an electromagnet.
Uses: In electric motors; in electric bells (or any other valid use).

(b) Labelled Diagram:


(c) Purpose of soft iron core: The soft iron core is used to increase the strength of the electromagnet. Soft iron is chosen because it becomes magnetized easily when current flows and loses its magnetism quickly when the current is switched off, making it ideal for temporary magnets.

(d) Two ways to increase electromagnet strength:
1. By increasing the current passing through the solenoid.
2. By increasing the number of turns in the coil of the solenoid.

(i) Magnetic Field Lines Due to a Current Carrying Circular Loop:
When current flows through a circular loop, it produces magnetic field lines around the wire. These field lines form concentric circles around the wire, which become larger as we move away from the wire. At the centre of the loop, these lines appear as straight lines. The magnetic field is strongest at the centre and weaker as you move away from it.



(ii) The magnetic field produced by a current-carrying wire at any given point depends directly on the current passing through it. For a circular coil with n turns, the current in each turn flows in the same direction, so the magnetic fields due to each turn add up together. Therefore, the total magnetic field strength increases proportionally with the number of turns — making it n times as large as the field produced by a single turn.

Right Hand Thumb Rule: If you hold the current-carrying conductor in your right hand with your thumb pointing in the direction of the current, the direction in which your fingers curl gives the direction of the magnetic field lines around the conductor.

Explanation for the Given Case:
In this case, the current flows vertically downwards. According to the Right Hand Thumb Rule, when you point your thumb downwards (in the direction of the current), your fingers curl in a clockwise direction around the conductor. This means the magnetic field lines will be clockwise around the conductor when viewed from above.

Diagram:

(a) The North poles of magnets A and B are facing each other.

(b) Magnetic field lines never intersect each other because the intersection of magnetic field lines would imply that there are two directions for the magnetic field at the same point, which is not physically possible. At any point in a magnetic field, there can be only one direction of the field.

(c) Dependence of magnetic field strength at the centre of a current-carrying circular coil:

(i) Radius of the coil: The magnetic field strength is inversely proportional to the radius of the coil. The larger the radius, the weaker the magnetic field at the centre.

(ii) Number of turns in the coil: The magnetic field strength is directly proportional to the number of turns. More turns lead to a stronger magnetic field at the centre.

(iii) Strength of the current flowing in the coil: The magnetic field strength is directly proportional to the current. More current results in a stronger magnetic field at the centre.

(a) Schematic Labelled Diagram of Domestic Electric Circuit:


(b)(i) Fuse in an electric circuit:
A fuse is necessary to prevent damage to appliances due to overloading or short-circuiting. It acts as a safety device by breaking the circuit if the current exceeds a safe limit, thus preventing further damage or the risk of fire.

(b)(ii) Earth wire to electric appliances with metallic body:
An earth wire is connected to the metallic body of an electric appliance and buried deep in the earth. It provides a low-resistance conducting path for current in case of leakage. If the appliance’s metallic body becomes live due to a fault, the earth wire directs the current safely to the ground, preventing electric shock to the user. This is why an earth wire is an essential safety measure.