Magnetic Effects of Electric Current — Class 10 Physics NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 10 Physics chapter "Magnetic Effects of Electric Current" — 10 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 10 Physics chapter "Magnetic Effects of Electric Current" — 10 important questions with detailed answers f…

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NCERT Solutions for Class 10 Physics — Magnetic Effects of Electric Current. Step-by-step answers to all 10 textbook questions from this chapter, written for CBSE board preparation and free to use.

Magnetic Effects of Electric Current — All 10 Questions Solved

Q1. Draw magnetic field lines around a bar magnet. List any three important properties of these magnetic field lines.

1. Drawing Magnetic Field Lines:
Imagine a bar magnet with a North (N) pole and a South (S) pole. The magnetic field lines emerge from the North pole and enter the South pole outside the magnet. Inside the magnet, they travel from the South pole to the North pole, forming continuous closed loops.

(Since I cannot draw, mentally visualize this: lines curving out from N, entering S, and continuing straight from S to N inside the magnet.)

2. Properties of Magnetic Field Lines:
a. Closed Loops: Magnetic field lines are continuous closed curves. They emerge from the North pole and merge into the South pole outside the magnet. Inside the magnet, they travel from the South pole to the North pole.
b. Do Not Intersect: No two magnetic field lines ever intersect each other. If they did, it would mean that at the point of intersection, the compass needle would point in two different directions, which is not possible.
c. Direction: The direction of the magnetic field at any point is given by the tangent to the field line at that point. A compass needle placed at that point would align itself along the tangent, with its North pole pointing in the direction of the field.
d. Strength of Field: The magnetic field is stronger where the field lines are crowded (closer to each other), such as near the poles. The field is weaker where the lines are farther apart.
e. Pole Origin/Termination: Field lines originate from the North pole and terminate at the South pole (outside the magnet).

Q2. A straight conductor carries current vertically upwards. What is the direction of the magnetic field at a point: (a) to the east of the conductor? (b) to the west of the conductor?

To determine the direction of the magnetic field around a straight current-carrying conductor, we use the Right-Hand Thumb Rule.

Steps using Right-Hand Thumb Rule:
1. Hold the conductor: Imagine holding the straight conductor in your right hand.
2. Point the thumb: Your thumb should point in the direction of the current. In this case, the current is flowing vertically upwards.
3. Curl the fingers: Your fingers will curl around the conductor in the direction of the magnetic field lines.

Applying to the given points:
Let's assume we are looking down from above, with North at the top, South at the bottom, East to the right, and West to the left.

* Current Direction: Vertically Upwards.

(a) At a point to the east of the conductor:
* With your thumb pointing upwards, your fingers will curl in an anti-clockwise direction when viewed from above.
* At a point to the east of the wire, your fingers would be pointing towards the North.
* Therefore, the direction of the magnetic field to the east of the conductor is North.

(b) At a point to the west of the conductor:
* Continuing the anti-clockwise curl, at a point to the west of the wire, your fingers would be pointing towards the South.
* Therefore, the direction of the magnetic field to the west of the conductor is South.

Q3. How does the magnetic field inside a current-carrying solenoid compare to that of a bar magnet? List two factors on which the strength of the magnetic field produced by a solenoid depends.

1. Comparison of Magnetic Field:
* A current-carrying solenoid produces a magnetic field similar to that of a bar magnet. Both have a North pole at one end and a South pole at the other.
* The magnetic field lines inside a solenoid are nearly parallel to the axis of the solenoid and are uniformly distributed. This indicates that the magnetic field is uniform and strong inside the solenoid, much like the magnetic field within a bar magnet (though we usually visualize the external field of a bar magnet).
* Outside the solenoid, the field lines resemble those of a bar magnet, emerging from one end and entering the other, forming closed loops.

2. Factors Affecting the Strength of Magnetic Field in a Solenoid:
The strength of the magnetic field produced by a current-carrying solenoid depends on the following factors:
a. Magnitude of Current: The magnetic field strength is directly proportional to the current flowing through the solenoid. More current means a stronger magnetic field.
b. Number of Turns per Unit Length: The magnetic field strength is directly proportional to the number of turns of the coil per unit length (N/L). A solenoid with more turns packed into the same length will produce a stronger field.
c. Nature of the Core Material: Inserting a soft iron core (or any ferromagnetic material) inside the solenoid significantly increases the strength of the magnetic field. This is because ferromagnetic materials can be easily magnetized and concentrate the magnetic field lines.

Q4. A straight conductor is placed perpendicular to a uniform magnetic field. When a current flows through the conductor, it experiences a force. If the direction of current is reversed, what happens to the direction of the force? State the rule used to determine the direction of force.

1. Effect of Reversing Current on Force Direction:
When the direction of the current flowing through the conductor is reversed, the direction of the force experienced by the conductor will also be reversed.

* Reasoning: The direction of the force on a current-carrying conductor in a magnetic field depends on both the direction of the current and the direction of the magnetic field. This relationship is described by Fleming's Left-Hand Rule. If one of these (current or field) is reversed while the other remains the same, the direction of the force will reverse.

2. Rule Used to Determine the Direction of Force:
The rule used to determine the direction of the force (or motion) experienced by a current-carrying conductor placed in a magnetic field is Fleming's Left-Hand Rule.

Explanation of Fleming's Left-Hand Rule:
* Stretch the thumb, forefinger, and middle finger of your left hand such that they are mutually perpendicular to each other.
* If the forefinger points in the direction of the magnetic field (from North to South).
* And the middle finger points in the direction of the current.
* Then the thumb will point in the direction of the force (or motion) experienced by the conductor.

Q5. State the principle of an electric motor. Explain the role of a split-ring commutator in a DC electric motor.

1. Principle of an Electric Motor:
An electric motor works on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a force. If the conductor is arranged in the form of a coil and placed between the poles of a magnet, the forces on the opposite sides of the coil act in opposite directions, causing the coil to rotate continuously.
In simpler terms: Electrical energy is converted into mechanical energy (rotational motion).

2. Role of a Split-Ring Commutator in a DC Electric Motor:
A split-ring commutator is a crucial component in a DC electric motor that ensures the continuous rotation of the motor coil in the same direction.

* Function: It is a device that reverses the direction of the current flowing through the coil after every half rotation (180 degrees).
* How it works: The commutator consists of two (or more) semicircular rings, insulated from each other, to which the ends of the coil are connected. These rings make contact with two stationary carbon brushes, which are connected to the external power supply.
* During rotation: As the coil rotates, the brushes lose contact with one segment of the commutator and make contact with the other segment after every half rotation. This switching of contacts effectively reverses the direction of current in the coil relative to the magnetic field.
* Importance: Without the commutator, the direction of the force on the coil sides would reverse after every half rotation, causing the coil to oscillate back and forth instead of rotating continuously in one direction. The commutator ensures that the torque (turning effect) on the coil always acts in the same direction, leading to continuous unidirectional rotation.

Q6. Describe an experiment to demonstrate electromagnetic induction. What factors affect the magnitude of the induced current?

1. Experiment to Demonstrate Electromagnetic Induction:
Aim: To demonstrate that a current can be induced in a coil by changing the magnetic field around it.

Materials: A coil of wire, a strong bar magnet, a sensitive galvanometer.

Procedure:
a. Connect the two ends of the coil of wire to a galvanometer. The galvanometer is used to detect the presence and direction of current.
b. First Observation: Take the bar magnet and rapidly move its North pole towards the coil. Observe the galvanometer. You will notice a momentary deflection in the galvanometer needle, indicating the production of an induced current in the coil.
c. Second Observation: Now, rapidly move the North pole of the magnet away from the coil. Observe the galvanometer again. You will see a momentary deflection in the opposite direction, indicating that the induced current's direction has reversed.
d. Third Observation: If you hold the magnet stationary inside the coil (or outside it), the galvanometer shows no deflection, meaning no current is induced.
e. Fourth Observation: Repeat steps (b) and (c) by using the South pole of the magnet. You will observe similar deflections, but in opposite directions compared to using the North pole for the same motion.

Conclusion: This experiment demonstrates that a change in the magnetic field lines linked with a coil induces an electric current in the coil. This phenomenon is called electromagnetic induction.

2. Factors Affecting the Magnitude of the Induced Current:
The magnitude of the induced current in a coil depends on the following factors:
a. Speed of Relative Motion: The faster the relative motion between the coil and the magnet (i.e., the faster the magnet is moved towards or away from the coil, or vice-versa), the greater the rate of change of magnetic flux, and thus the larger the induced current.
b. Strength of the Magnetic Field: A stronger magnet will produce a stronger magnetic field, leading to a larger induced current.
c. Number of Turns in the Coil: If the coil has more turns, the induced current will be larger, as each turn contributes to the induced electromotive force (EMF).
d. Area of the Coil: A larger cross-sectional area of the coil allows more magnetic field lines to pass through, contributing to a greater change in magnetic flux and thus a larger induced current.

Q7. A coil is rotated clockwise in a magnetic field. If the magnetic field lines are from North to South (left to right), and the coil's upward moving arm is on the left, what is the direction of the induced current in that arm? State the rule used.

To determine the direction of the induced current, we use Fleming's Right-Hand Rule.

Steps for applying Fleming's Right-Hand Rule:
1. Stretch fingers: Stretch the thumb, forefinger, and middle finger of your right hand so that they are mutually perpendicular to each other.
2. Point Forefinger (Field): The forefinger points in the direction of the magnetic field.
3. Point Thumb (Motion): The thumb points in the direction of the motion of the conductor.
4. Middle Finger (Current): The middle finger will then indicate the direction of the induced current.

Applying to the given situation:
* Direction of Magnetic Field (Forefinger): From North to South, which is given as left to right.
* Direction of Motion of the Arm (Thumb): The arm on the left is described as moving upwards.

Let's apply the rule:
1. Point your forefinger towards the right (direction of magnetic field).
2. Point your thumb upwards (direction of motion of the conductor).
3. Now, observe the direction in which your middle finger points. It will point inwards (into the page/plane of the coil).

Conclusion: The direction of the induced current in that arm of the coil is inwards (or perpendicular to the plane of the coil, away from the observer).

Rule used: Fleming's Right-Hand Rule is used to determine the direction of induced current when a conductor moves in a magnetic field.

Q8. Differentiate between Direct Current (DC) and Alternating Current (AC). Why is AC preferred over DC for long-distance transmission of electric power?

1. Differentiation between Direct Current (DC) and Alternating Current (AC):

2. Why AC is preferred over DC for long-distance transmission of electric power:
AC is overwhelmingly preferred over DC for long-distance transmission of electric power for the following key reasons:

a. Voltage Transformation: AC voltages can be easily stepped up (increased) or stepped down (decreased) using transformers. For long-distance transmission, AC is stepped up to very high voltages (e.g., 11 kV, 33 kV, 132 kV, 400 kV) and therefore very low currents.

b. Reduced Power Loss: Power loss during transmission through cables is given by the formula P_loss = I²R, where I is the current and R is the resistance of the transmission lines. By stepping up the voltage, the current (I) in the transmission lines is significantly reduced (since Power = V x I, for a given power, higher V means lower I). A lower current drastically reduces the I²R losses, making transmission much more efficient and economical.

c. Cost-Effectiveness: Due to reduced power losses, smaller diameter (and thus less expensive) cables can be used for transmission, further reducing costs.

DC current cannot be easily stepped up or down. While DC transmission is used in specific situations (like undersea cables or for very long distances point-to-point without intermediate taps), the advantages of AC for general grid distribution far outweigh DC.

Q9. Explain the function of a fuse in a domestic electric circuit. How does overloading occur, and what are its consequences?

1. Function of a Fuse in a Domestic Electric Circuit:
A fuse is a crucial safety device used in domestic electric circuits. Its primary function is to protect electrical appliances and the wiring from damage due to excessive current (overcurrent).

* Construction: A fuse contains a short piece of wire made of a material with a low melting point (e.g., an alloy of lead and tin) and high resistance. It is connected in series with the live wire of the circuit.
* Working: When the current in the circuit exceeds a safe limit (due to overloading or short-circuiting), the fuse wire heats up rapidly (due to the heating effect of current, H = I²Rt). Since it has a low melting point, it quickly melts and breaks the circuit. This instantly stops the flow of current to the appliances and wiring, preventing potential damage, electrical fires, and electric shocks.
* Safety: Once the fuse blows, it needs to be replaced with a new one of the appropriate rating after the fault is rectified.

2. How Overloading Occurs and its Consequences:
Overloading occurs when too many electrical appliances or devices, each drawing a certain amount of current, are connected to a single circuit or a single power socket simultaneously. The total current drawn by these appliances then exceeds the safe current carrying capacity of the household wiring.

Causes of Overloading:
* Connecting multiple high-power appliances (like heaters, air conditioners, geysers, refrigerators, washing machines) to the same circuit/socket.
* Using multi-plug adaptors to connect several devices to one outlet.

Consequences of Overloading:
a. Overheating of Wires: When current exceeds the safe limit, the wires in the circuit heat up excessively (I²R heating). This can melt the insulation around the wires.
b. Fire Hazard: Prolonged overheating of wires due to overloading can lead to an electrical fire, especially if flammable materials are nearby.
c. Damage to Appliances: High currents can damage the internal components of connected appliances.
d. Blowing Fuses/Tripping Circuit Breakers: Fortunately, in well-designed circuits, a fuse will melt or a Miniature Circuit Breaker (MCB) will trip, breaking the circuit and preventing further damage or hazards.

Q10. A student performing an experiment places a straight current-carrying wire horizontally, running from East to West, on a table. The current flows from West to East. A compass is placed directly below the wire. In which direction will the North pole of the compass needle deflect? Justify your answer.

To determine the direction of the magnetic field and hence the compass needle's deflection, we use the Right-Hand Thumb Rule.

Steps for application:
1. Identify Current Direction: The current flows from West to East. (Imagine a map: West on your left, East on your right).
2. Point Thumb: Place your right hand with your thumb pointing in the direction of the current, i.e., towards the East.
3. Curl Fingers: Curl your fingers around the imaginary wire. Your fingers represent the direction of the magnetic field lines.
4. Observe Below the Wire: We need to find the direction of the magnetic field at a point directly below the wire.
* With your thumb pointing East, if you visualize your fingers curling, above the wire they point North, and below the wire, they point South.

Conclusion:
* The magnetic field lines at the point directly below the wire will be directed towards the South.
* A compass needle's North pole always points in the direction of the magnetic field.

Therefore, the North pole of the compass needle placed directly below the wire will deflect towards the South direction.

Magnetic Effects of Electric Current — Practice MCQs with Answers

Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.

MCQ 1. The magnetic field lines produced around a straight current-carrying conductor are:

A. Straight lines parallel to the conductor
B. Straight lines perpendicular to the conductor
C. Concentric circles centered on the conductor
D. Helical lines

Answer: C. Concentric circles centered on the conductor — According to the Right-Hand Thumb Rule, the magnetic field lines around a straight current-carrying conductor are concentric circles whose center lies on the conductor.

MCQ 2. A compass needle is placed near a straight current-carrying conductor. If the current flows from south to north, what will be the direction of deflection of the north pole of the compass needle when placed directly above the conductor?

A. Towards East
B. Towards West
C. Towards North
D. Towards South

Answer: B. Towards West — Using the Right-Hand Thumb Rule, point the thumb in the direction of current (North). Curl your fingers. Above the wire, the magnetic field lines point towards the West. Therefore, the north pole of the compass needle will deflect towards the West.

MCQ 3. Which of the following factors does NOT affect the strength of an electromagnet?

A. Number of turns in the coil
B. Current flowing through the coil
C. Nature of the core material
D. Diameter of the coil wire

Answer: D. Diameter of the coil wire — The strength of an electromagnet depends on the number of turns in the coil, the current flowing through it, and the nature of the core material (e.g., soft iron increases strength). The diameter of the coil wire primarily affects its resistance, not directly the magnetic field strength for a given current.

MCQ 4. A current-carrying conductor is placed in a magnetic field. The force experienced by the conductor is maximum when the angle between the direction of current and the magnetic field is:

A. 0 degrees
B. 45 degrees
C. 90 degrees
D. 180 degrees

Answer: C. 90 degrees — The force experienced by a current-carrying conductor in a magnetic field is maximum when the conductor is placed perpendicular to the magnetic field (angle = 90 degrees). The force is given by F = BILsinθ, where F is maximum when sinθ = 1.

MCQ 5. An electric motor converts:

A. Electrical energy into mechanical energy
B. Mechanical energy into electrical energy
C. Chemical energy into electrical energy
D. Mechanical energy into sound energy

Answer: A. Electrical energy into mechanical energy — An electric motor is a device that converts electrical energy into mechanical energy, typically causing rotation.

MCQ 6. Inside a current-carrying solenoid, the magnetic field lines are:

A. Circular and concentric
B. Straight and parallel to the axis
C. Straight and perpendicular to the axis
D. Diverging from one end and converging at the other

Answer: B. Straight and parallel to the axis — Inside a current-carrying solenoid, the magnetic field is uniform and strong. The magnetic field lines are parallel to the axis of the solenoid, indicating a uniform field.

MCQ 7. A horizontal power line carries current from east to west. What is the direction of the magnetic field directly below the power line?

A. North to South
B. South to North
C. Vertically upwards
D. Vertically downwards

Answer: B. South to North — Using the Right-Hand Thumb Rule, point the thumb in the direction of current (West). Curl your fingers. Below the wire, the magnetic field lines point towards the North (from South to North relative to the wire's immediate surroundings).

MCQ 8. The phenomenon of electromagnetic induction is:

A. The process of charging a body
B. The process of generating magnetic field due to current
C. The process of producing induced current by changing magnetic field
D. The process of converting mechanical energy into chemical energy

Answer: C. The process of producing induced current by changing magnetic field — Electromagnetic induction is the phenomenon where an electric current (induced current) is produced in a conductor due to a change in the magnetic field linked with it.

MCQ 9. Which rule is used to find the direction of induced current in an electric generator?

A. Right-Hand Thumb Rule
B. Fleming's Left-Hand Rule
C. Fleming's Right-Hand Rule
D. Maxwell's Corkscrew Rule

Answer: C. Fleming's Right-Hand Rule — Fleming's Right-Hand Rule is used to determine the direction of the induced current in a conductor moving in a magnetic field, which is the principle behind an electric generator.

MCQ 10. A fuse wire is used in domestic circuits to:

A. Increase the current flow
B. Reduce the voltage
C. Protect appliances from high current
D. Convert AC to DC

Answer: C. Protect appliances from high current — A fuse wire has a low melting point and high resistance. It melts and breaks the circuit when the current exceeds a safe limit, thus protecting appliances from damage due to overloading or short-circuiting.

MCQ 11. A circular loop of wire carries current in a clockwise direction. The direction of the magnetic field lines passing through the plane of the loop is:

A. Parallel to the plane of the loop
B. Perpendicular to the plane of the loop, pointing outwards
C. Perpendicular to the plane of the loop, pointing inwards
D. Varies depending on position within the loop

Answer: C. Perpendicular to the plane of the loop, pointing inwards — Using the Right-Hand Thumb Rule (curling fingers in the direction of current), if the current in a circular loop is clockwise, the magnetic field lines passing through the plane of the loop are directed inwards, perpendicular to the plane.

MCQ 12. What is the main difference between an AC generator and a DC generator?

A. AC generator uses a stronger magnetic field.
B. DC generator has a commutator while AC generator uses slip rings.
C. AC generator produces higher voltage.
D. DC generator works on the principle of electromagnetic induction, while AC generator does not.

Answer: B. DC generator has a commutator while AC generator uses slip rings. — The main structural difference between an AC and DC generator lies in the type of rings used. An AC generator uses slip rings, while a DC generator uses a split-ring commutator to ensure unidirectional current in the external circuit.

MCQ 13. The function of the earth wire in domestic electrical circuits is to:

A. Provide a path for high current during normal operation.
B. Supply extra power to appliances.
C. Ensure that any leakage current flows to the ground, preventing electric shock.
D. Reduce the resistance of the circuit.

Answer: C. Ensure that any leakage current flows to the ground, preventing electric shock. — The earth wire provides a safety path for leakage current from the metallic body of an appliance to flow directly into the ground, thereby preventing a user from getting an electric shock in case of an insulation failure.

MCQ 14. Overloading in an electrical circuit occurs when:

A. The current drawn is less than the rated current.
B. The live and neutral wires come into direct contact.
C. Too many appliances are connected to a single socket.
D. The voltage supply is too low.

Answer: C. Too many appliances are connected to a single socket. — Overloading occurs when too many electrical appliances are connected to a single socket, causing a large current to be drawn from the circuit. This excessive current can overheat the wiring and cause a fire.

MCQ 15. A straight conductor carries current vertically upwards. When placed in a magnetic field directed from west to east, the conductor will experience a force:

A. Towards North
B. Towards South
C. Vertically downwards
D. Towards East

Answer: A. Towards North — Apply Fleming's Left-Hand Rule. Point the forefinger (magnetic field) from West to East. Point the middle finger (current) vertically upwards. The thumb (force) will point towards the North.

MCQ 16. Magnetic field lines:

A. Always intersect each other
B. Emerge from the South pole and merge into the North pole
C. Do not intersect each other
D. Are always straight lines

Answer: C. Do not intersect each other — Magnetic field lines never intersect each other because if they did, it would mean that at the point of intersection, the compass needle would point in two different directions, which is not possible.

MCQ 17. To increase the strength of the magnetic field produced by a solenoid, which of the following actions would be most effective?

A. Decreasing the current
B. Using a copper core
C. Increasing the number of turns per unit length
D. Decreasing the length of the solenoid while keeping turns constant

Answer: C. Increasing the number of turns per unit length — The magnetic field strength inside a solenoid is directly proportional to the current flowing through it and the number of turns per unit length. Increasing the number of turns per unit length significantly strengthens the field.

MCQ 18. A rectangular coil is rotated clockwise in a uniform magnetic field. At an instant when the side AB is moving upwards and side CD is moving downwards (assuming the coil is oriented vertically, and the field is horizontal from left to right), the direction of induced current in the coil will be:

A. From A to B and C to D
B. From B to A and D to C
C. From A to B and D to C
D. From B to A and C to D

Answer: B. From B to A and D to C — Apply Fleming's Right-Hand Rule. For side AB: motion is upwards, field is left to right. The induced current flows from B to A. For side CD: motion is downwards, field is left to right. The induced current flows from D to C. So the overall current direction in the loop is B to A and D to C.

MCQ 19. What happens during a short circuit?

A. The current in the circuit decreases significantly.
B. The resistance of the circuit increases significantly.
C. The live wire and the neutral wire come into direct contact.
D. The voltage across the circuit drops to zero.

Answer: C. The live wire and the neutral wire come into direct contact. — A short circuit occurs when the live wire and the neutral wire come into direct contact, bypassing the appliance. This causes the circuit resistance to drop drastically, leading to a very large current flow.

MCQ 20. The split rings in a DC motor act as a:

A. Commutator
B. Slip ring
C. Brush
D. Armature

Answer: A. Commutator — The split rings in a DC motor form a commutator, which reverses the direction of current flowing through the coil every half rotation, ensuring that the torque on the coil is always in the same direction, leading to continuous rotation.

How to Use These Solutions

Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.

Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.

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