Magnetism and Matter

Assertion and Reason Questions Chapter-5 Magnetism and Matter

Assertion (A) and other labelled Reason (R). Select the correct answer to these questions from the options as given below.

A. Both A and R are true, and R is the correct explanation of A.

B. Both A and R are true, but R is not the correct explanation of A.

C. A is true, but R is false.

D. A is false, but R is true.

1. Assertion (A): The magnetic field inside a long solenoid is uniform.

Reason (R): The magnetic field lines are parallel and equidistant inside the solenoid.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The uniformity of the magnetic field inside a long solenoid is due to the parallel and equidistant nature of the field lines.

2. Assertion (A): A magnetic dipole moment is a vector quantity.

Reason (R): It has both magnitude and direction.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The magnetic dipole moment has a defined direction along the axis of the magnetic dipole, indicating its vector nature.

3. Assertion (A): The Earth’s magnetic field is approximately uniform over small regions.

Reason (R): The distance between the magnetic poles is large compared to the dimensions of small regions on Earth.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The uniformity of the Earth's magnetic field in small regions arises from the large distance between the magnetic poles.

4. Assertion (A): The magnetic field due to a straight current-carrying conductor is circular.

Reason (R): The field lines form concentric circles around the conductor.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The circular nature of the magnetic field lines around a straight conductor confirms that they are concentric circles.

5. Assertion (A): Magnetic field lines never intersect each other.

Reason (R): If they did intersect, it would indicate two different directions for the magnetic field at the same point.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The non-intersection of magnetic field lines ensures that there is only one direction of the magnetic field at any point in space.

6. Assertion (A): A magnetic field can exert a force on a stationary charged particle.

Reason (R): The magnetic force is independent of the velocity of the particle.

• (b) Both A and R are true, but R is not the correct explanation of A.
• Answer: (b)
  Explanation: A magnetic field cannot exert a force on a stationary charged particle; the force is dependent on the velocity of the charge.

7. Assertion (A): The direction of the magnetic field inside a solenoid is the same as the direction of the current.

Reason (R): The right-hand grip rule applies to current-carrying solenoids.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: According to the right-hand grip rule, the direction of the magnetic field inside a solenoid follows the direction of the current flow.

8. Assertion (A): The magnetic field strength inside a solenoid increases with the number of turns per unit length.

Reason (R): The magnetic field strength is directly proportional to the number of turns.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The magnetic field inside a solenoid is given by B= \(\ {μ_0}nI \) , where nnn is the number of turns per unit length.

9. Assertion (A): The magnetic field of the Earth can affect a compass needle.

Reason (R): The compass needle is a small bar magnet.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The interaction between the Earth's magnetic field and the magnetic field of the compass needle allows it to align with the Earth's field.

10. Assertion (A): The force on a charged particle moving in a magnetic field is maximum when it moves perpendicular to the field lines.

Reason (R): The magnetic force depends on the angle between the velocity and the magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The force is maximized at 90∘ due to the sin⁡(θ) term in the force equation F=qvBsin⁡(θ).

11. Assertion (A): A magnetic field can be produced by a stationary charge.

Reason (R): Magnetic fields are produced by moving charges.

• (b) Both A and R are true, but R is not the correct explanation of A.
• Answer: (b)
  Explanation: Only moving charges produce magnetic fields; stationary charges produce electric fields.

12. Assertion (A): The magnetic field lines inside a magnet are directed from north to south.

Reason (R): The convention for magnetic field lines is to originate from the north pole and terminate at the south pole.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Magnetic field lines indeed flow from the north pole to the south pole inside the magnet.

13. Assertion (A): The magnitude of the magnetic force on a charged particle depends on the charge of the particle.

Reason (R): The force is given by the equation F=qvBsin⁡(θ).

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The equation shows that the force is directly proportional to the charge of the particle.

14. Assertion (A): The Earth's magnetic field can be approximated as a dipole field.

Reason (R): The Earth has two magnetic poles similar to a bar magnet.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The dipole approximation is valid as the Earth behaves like a giant bar magnet with distinct magnetic poles.

15. Assertion (A): A current loop in a magnetic field experiences a torque.

Reason (R): Torque is the product of force and the distance from the pivot.

• (b) Both A and R are true, but R is not the correct explanation of A.
• Answer: (b)
  Explanation: Torque arises from the magnetic forces on the current loop, not simply the product of force and distance.

16. Assertion (A): The magnetic field produced by a solenoid can be used to magnetize materials.

Reason (R): The solenoid's magnetic field is strong and uniform.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The uniform and strong field inside a solenoid effectively magnetizes materials placed within it.

17. Assertion (A): The magnetic force on a charged particle is independent of its speed.

Reason (R): The magnetic force acts on the charge only, not its motion.

• (b) Both A and R are true, but R is not the correct explanation of A.
• Answer: (b)
  Explanation: The magnetic force depends on the speed of the charged particle; it increases with higher speed.

18. Assertion (A): The direction of the magnetic field due to a circular current loop can be determined using the right-hand grip rule.

Reason (R): The rule states that the fingers of the right hand follow the current direction.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The right-hand grip rule effectively indicates the direction of the magnetic field inside a circular current loop.

19. Assertion (A): A magnetic field can induce current in a closed loop.

Reason (R): This phenomenon is described by Faraday's law of electromagnetic induction.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Faraday's law explains how a changing magnetic field can induce emf and current in a closed loop.

20. Assertion (A): A current-carrying conductor experiences a force when placed in an external magnetic field.

Reason (R): The force arises due to the interaction between the magnetic field and the conductor's magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The interaction between the external magnetic field and the magnetic field produced by the current in the conductor leads to a force.

21. Assertion (A): The magnetic field lines can be visualized using iron filings.

Reason (R): Iron filings align along the magnetic field lines, showing the field's direction and strength.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Iron filings behave as small magnets and align with the magnetic field, providing a clear visualization of its pattern.

22. Assertion (A): The magnetic moment of a loop of wire increases with an increase in current.

Reason (R): The magnetic moment is directly proportional to the current flowing through the loop.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The magnetic moment mmm is given by m=nIA, where nnn is the number of turns, I is the current, and A is the area.

23. Assertion (A): The force between two parallel currents is attractive if the currents flow in the same direction.

Reason (R): Parallel currents create magnetic fields that attract each other.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The magnetic field produced by one current affects the other, leading to attraction when currents flow in the same direction.

24. Assertion (A): Magnetic field lines are closed loops.

Reason (R): There are no magnetic monopoles found in nature.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The absence of magnetic monopoles means that magnetic field lines must always form closed loops.

25. Assertion (A): The magnetic field of a bar magnet is strongest at its poles.

Reason (R): The field lines are closest together at the poles, indicating a strong field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The density of magnetic field lines correlates with field strength, making poles the strongest areas.

26. Assertion (A): Magnetic susceptibility is a measure of the degree of magnetization of a material in response to an applied magnetic field.

Reason (R): It is defined as the ratio of the intensity of magnetization to the intensity of the applied magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Magnetic susceptibility quantitatively describes how easily a material can be magnetized by an external field.

27. Assertion (A): A charged particle moving parallel to a magnetic field experiences a magnetic force.

Reason (R): The magnetic force acts on all moving charges.

• (b) Both A and R are true, but R is not the correct explanation of A.
• Answer: (b)
  Explanation: A charged particle moving parallel to a magnetic field experiences no force; the force is maximum when moving perpendicular.

28. Assertion (A): Magnetic fields can exist in a vacuum.

Reason (R): Magnetic fields do not require a medium to propagate.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Magnetic fields can exist in a vacuum, as they are produced by moving charges and do not depend on a medium.

29. Assertion (A): The force on a current-carrying conductor in a magnetic field can be increased by increasing the magnetic field strength.

Reason (R): The force is directly proportional to the magnetic field strength.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The magnetic force on a conductor is given by F=BILsin⁡(θ), indicating direct proportionality to the magnetic field strength.

30. Assertion (A): Magnetic lines of force diverge from the north pole of a magnet.

Reason (R): This indicates the direction of the magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Magnetic lines of force indicate the direction of the magnetic field, originating from the north pole.

31. Assertion (A): The magnetization of materials can be increased by increasing the applied magnetic field.

Reason (R): Magnetization is proportional to the external magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: Increasing the external magnetic field enhances the magnetization of the material.

32. Assertion (A): A current-carrying loop experiences a force in a magnetic field.

Reason (R): The loop generates its own magnetic field, which interacts with the external field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The interaction between the loop's magnetic field and the external field produces a net force on the loop.

33. Assertion (A): The Earth behaves like a giant bar magnet.

Reason (R): The magnetic field of the Earth resembles that of a dipole.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The Earth’s magnetic field can be approximated as a dipole field, supporting the analogy of a bar magnet.

34. Assertion (A): Electromagnets are used in various applications due to their controllable magnetic field.

Reason (R): The strength of an electromagnet can be varied by changing the current.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The ability to control the current allows for adjustable magnetic fields, making electromagnets versatile.

35. Assertion (A): The magnetic field is strongest at the center of a current-carrying circular loop.

Reason (R): The magnetic field lines converge at the center of the loop.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The convergence of field lines at the center of a circular loop results in a stronger magnetic field.

36. Assertion (A): A magnetic compass can be used to detect the direction of a magnetic field.

Reason (R): The compass needle aligns with the magnetic field lines.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The alignment of the compass needle with the magnetic field allows it to indicate the direction of the field.

37. Assertion (A): The magnetic field can do work on a charged particle.

Reason (R): The magnetic force is perpendicular to the velocity of the particle.

• (b) Both A and R are true, but R is not the correct explanation of A.
• Answer: (b)
  Explanation: The magnetic force does no work on a charged particle because it is always perpendicular to the direction of motion.

38. Assertion (A): The force on a charged particle in a magnetic field is given by the equation F=qvBsin⁡(θ).

Reason (R): The equation shows that the force depends on the angle between the velocity and the magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The equation indeed expresses the dependence of the force on the angle between the charge's velocity and the magnetic field.

39. Assertion (A): A current-carrying conductor experiences a torque when placed in a magnetic field.

Reason (R): Torque arises due to the interaction of the magnetic field with the current in the conductor.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The interaction between the magnetic field and the current produces a torque, which tends to align the conductor with the field.

40. Assertion (A): The energy density of a magnetic field is given by \(\frac{B^2} {2 u_0}\)​​.

Reason (R): This formula indicates how much energy is stored per unit volume in the magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The energy density formula quantifies the energy stored in the magnetic field, providing insights into its energy characteristics.

41. Assertion (A): Magnetic materials can be classified as diamagnetic, paramagnetic, or ferromagnetic.

Reason (R): The classification depends on the material's response to an applied magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The behavior of materials in response to magnetic fields categorizes them into the specified groups based on their magnetic properties.

42. Assertion (A): An object can be magnetized by rubbing it with a magnet.

Reason (R): Rubbing aligns the magnetic domains in the object.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The mechanical action of rubbing aligns the domains, resulting in the magnetization of the material.

43. Assertion (A): The magnetic field inside a long solenoid is uniform and strong.

Reason (R): The magnetic field strength inside a solenoid is determined by the current and the number of turns per unit length.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The magnetic field inside a solenoid is uniform and can be expressed as B=μ0nI, supporting the assertion.

44. Assertion (A): The direction of the magnetic field around a current-carrying conductor can be determined using the right-hand rule.

Reason (R): The right-hand rule provides a method to visualize the orientation of the magnetic field lines.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The right-hand rule illustrates the direction of the magnetic field around the conductor based on the current's direction.

45. Assertion (A): The Earth's magnetic field is subject to changes over time.

Reason (R): The movement of molten iron in the Earth's outer core affects the magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The dynamic behavior of the molten iron generates changes in the magnetic field, confirming the assertion.

46. Assertion (A): The magnetic field due to a loop of wire is similar to that of a bar magnet.

Reason (R): Both configurations produce a dipole magnetic field.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The magnetic field produced by a current loop resembles that of a bar magnet, supporting the analogy.

47. Assertion (A): The magnetic field inside a hollow solenoid is zero.

Reason (R): The field lines inside the hollow region of a solenoid do not close.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The absence of current in the hollow region leads to no magnetic field being present, making the assertion valid.

48. Assertion (A): A magnetic field can exert forces on other magnets.

Reason (R): The magnetic fields of the magnets interact with each other.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The interaction of the magnetic fields of two magnets results in attractive or repulsive forces between them.

49. Assertion (A): An electric current produces a magnetic field around it.

Reason (R): This phenomenon is the basis for the functioning of electric motors.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The production of a magnetic field by an electric current is fundamental to the operation of electric motors and generators.

50. Assertion (A): The strength of the magnetic field produced by a straight current-carrying conductor decreases with distance.

Reason (R): The magnetic field lines spread out as the distance from the conductor increases.

• (a) Both A and R are true, and R is the correct explanation of A.
• Answer: (a)
  Explanation: The inverse relationship between distance and magnetic field strength results from the spreading of field lines as one moves away from the source.