📘 Welcome
Hi User, you have selected Read Mode.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
This is Time Free Mode for your convenience to understand every question as per your Ease and Time.
Here You get Answer and Details button. After mastering this mode, you can go for a test with Test Mode on the main page designed especially with Exam Features.
Q1. Devices that use current-carrying conductors and magnetic fields include:
Electric motors use current-carrying conductors placed in magnetic fields. The interaction between the current and the magnetic field produces a force that causes the motor to rotate. Heaters use the heating effect of current, solar cells convert light to electricity, and thermometers measure temperature.
Q2. The direction of rotation of the motor coil is determined using:
Fleming’s left-hand rule is used to determine the direction of force (and hence the direction of rotation) on a current-carrying conductor in a magnetic field. This rule is fundamental to understanding how electric motors work.
Q3. In Fleming’s left-hand rule, the middle finger represents the direction of:
In Fleming’s left-hand rule, the middle finger represents the direction of current. The forefinger represents the magnetic field, and the thumb represents the force or motion. The three fingers are held mutually perpendicular.
Q4. The forces acting on the two arms of the coil cause it to:
The forces acting on the two arms of the coil in a motor are in opposite directions, creating a couple (torque). This torque causes the coil to rotate. This is the basic principle of an electric motor.
Q5. When the magnetic field direction is reversed, the force on the rod:
When the magnetic field direction is reversed, the force on the rod also reverses. This is because the force depends on the direction of both the current and the magnetic field (F = BIL sin θ). Reversing either one reverses the force.
Q6. The combined study of electricity, magnetism, and motion forms the basis of:
The combined study of electricity, magnetism, and motion forms the basis of electromagnetic devices like motors, generators, and transformers. This is the foundation of electromagnetism.
Q7. The direction of force on the rod reverses when the direction of:
The direction of force on the rod reverses when the direction of current is reversed. This is because the force is given by F = BIL sin θ, and reversing I reverses the direction of the force.
Q8. Electromagnetic induction was discovered by:
Electromagnetic induction (the production of electric current by a changing magnetic field) was discovered by Michael Faraday in 1831. This discovery is the principle behind electric generators and transformers.
Q9. Electric generators work on the principle of:
Electric generators work on the principle of electromagnetic induction. When a coil rotates in a magnetic field, the magnetic flux through the coil changes, inducing an electric current. This converts mechanical energy into electrical energy.
Q10. In Fleming’s left-hand rule, current direction is taken as:
In Fleming’s left-hand rule, current direction is taken as the conventional current direction, which is opposite to the motion of electrons. Electrons flow from negative to positive, but conventional current flows from positive to negative.
Q11. The force acting on the electron in Example 4.2 is directed:
Q12. MRI is used for:
MRI (Magnetic Resonance Imaging) is used for medical diagnosis. It uses strong magnetic fields and radio waves to produce detailed images of the inside of the body, especially soft tissues like the brain and muscles.
Q13. The direction of induced current depends on the:
The direction of induced current depends on the direction of motion of the magnet (whether it is moving towards or away from the coil). This is given by Lenz’s law—the induced current opposes the change in magnetic flux.
Q14. In an electric motor, the coil is placed between:
In an electric motor, the coil is placed between two magnetic poles (north and south). The magnetic field from these poles interacts with the current in the coil to produce a force that rotates the coil.
Q15. An electric motor converts:
An electric motor converts electrical energy into mechanical energy. The current-carrying coil experiences a force in a magnetic field, causing it to rotate. This rotation can be used to do mechanical work.
Q16. The displacement of the aluminium rod shows that a force is exerted on a:
The displacement of the aluminium rod shows that a force is exerted on a current-carrying conductor placed in a magnetic field. This is the magnetic effect of electric current.
Q17. The force on a moving charge in a magnetic field is always:
The force on a moving charge in a magnetic field is always perpendicular to both the velocity of the charge and the magnetic field. This is given by F = qvB sin θ. The force is maximum when θ = 90°.
Q18. Using a soft iron core in a motor helps to:
Using a soft iron core in a motor helps to increase the magnetic field strength (and hence the power) of the motor. Soft iron becomes strongly magnetized in the presence of a magnetic field, intensifying the field.
Q19. The force on the conductor is maximum when current is at _____ to the magnetic field.
The force on the conductor is maximum when the current is at right angles (90°) to the magnetic field. The force is given by F = BIL sin θ, and sin 90° = 1, giving the maximum force.
Q20. The magnetic field produced inside the human body is mainly significant in the:
The magnetic fields produced inside the human body are mainly significant in the heart and brain. The heart produces magnetic fields due to electrical activity, which is measured by an ECG. The brain also produces weak magnetic fields measured by MEG (Magnetoencephalography).
Q21. The split ring in an electric motor acts as a:
The split ring (commutator) in an electric motor reverses the direction of current in the coil every half rotation. This ensures that the torque on the coil remains in the same direction, allowing continuous rotation.
Q22. MRI stands for:
MRI stands for Magnetic Resonance Imaging. It is a medical imaging technique that uses strong magnetic fields and radio waves to generate detailed images of organs and tissues inside the body.
Q23. The three fingers in Fleming’s left-hand rule are kept:
The three fingers in Fleming’s left-hand rule (thumb, forefinger, and middle finger) are kept mutually perpendicular (at right angles to each other). This helps determine the direction of force, magnetic field, and current.
Q24. The function of a commutator is to:
The function of a commutator (split ring) in a motor is to reverse the direction of current in the coil every half rotation. This ensures the coil continues to rotate in the same direction.
Q25. In the motor coil, current in arms AB and CD flows in:
In a motor coil, current in arms AB and CD flows in opposite directions because the current enters one arm and leaves through the other. This produces forces in opposite directions on the two arms, creating a couple that rotates the coil.
Q26. A moving magnet near a coil produces:
A moving magnet near a coil produces an electric current in the coil. This is electromagnetic induction—the changing magnetic field induces a current in the coil.
Q27. The direction of force on a current-carrying conductor depends on the direction of:
The direction of force on a current-carrying conductor depends on the direction of both the current and the magnetic field. The force is given by the cross product F = I(L × B), so reversing either reverses the force.
Q28. Weak electric currents in nerves produce:
Weak electric currents in nerves produce magnetic fields. These are very weak but can be detected using sensitive instruments like SQUIDs (Superconducting Quantum Interference Devices). This is the basis of techniques like MEG.
Q29. Electromagnetic induction occurs when there is a change in:
Electromagnetic induction occurs when there is a change in the magnetic field passing through a coil. The changing magnetic flux induces an electric current in the coil. The faster the change, the greater the induced current.
Q30. Continuous rotation of the motor coil is achieved due to repeated:
Continuous rotation of the motor coil is achieved due to repeated reversal of current in the coil. This is done by the commutator, which reverses the current every half rotation, ensuring the torque always acts in the same direction.
Q31. Fleming’s left-hand rule is used to find the direction of:
Fleming’s left-hand rule is used to find the direction of force or motion on a current-carrying conductor in a magnetic field. The thumb gives the direction of force, the forefinger gives the field direction, and the middle finger gives the current direction.
Q32. When the magnet stops moving, the galvanometer deflection becomes:
When the magnet stops moving, the galvanometer deflection becomes zero because there is no change in magnetic flux. Electromagnetic induction requires a changing magnetic field—if there is no change, there is no induced current.
Q33. Induced current exists only when there is:
Induced current exists only when there is continuous motion or change in the magnetic field. This is why electromagnetic induction requires a changing magnetic flux. When the motion stops, the current stops.
Q34. The magnetic fields produced by nerve currents are about _____ of Earth’s magnetic field.
The magnetic fields produced by nerve currents are about one-billionth of Earth’s magnetic field. This is why they are very difficult to detect and require extremely sensitive instruments.
Q35. In Fleming’s left-hand rule, the thumb represents the direction of:
In Fleming’s left-hand rule, the thumb represents the direction of motion or force on the conductor. The forefinger represents the magnetic field, and the middle finger represents the current.
Q36. The phenomenon of producing current by moving a magnet is called:
The phenomenon of producing electric current by moving a magnet near a coil is called electromagnetic induction. It was discovered by Michael Faraday and is the principle behind electric generators.
Q37. In Example 4.2, an electron enters a magnetic field at:
In Example 4.2, an electron enters a magnetic field at right angles (90°). This is the condition for maximum force on a moving charge in a magnetic field.
Q38. Which of the following appliances uses an electric motor?
An electric fan uses an electric motor to convert electrical energy into mechanical energy, which rotates the fan blades. Heaters use the heating effect, bulbs produce light, and fuses are safety devices.
Q39. The rectangular coil in an electric motor is made of:
The rectangular coil in an electric motor is made of insulated copper wire. Copper is a good conductor, and the insulation prevents short circuits between the turns of the coil.
Q40. In Fleming’s left-hand rule, the forefinger represents the direction of:
In Fleming’s left-hand rule, the forefinger represents the direction of the magnetic field. The middle finger represents current, and the thumb represents the force.
Q41. The electric motor works on the principle of:
The electric motor works on the principle of force on a current-carrying conductor placed in a magnetic field. The force causes the coil to rotate, converting electrical energy into mechanical energy.
Q42. Which of the following is NOT mentioned as a device using magnetic effects of current?
A barometer is used to measure atmospheric pressure and does not use magnetic effects of current. Microphones, loudspeakers, and refrigerators (which use motors) use magnetic effects of current.
Q43. Galvanometer is used to detect:
A galvanometer is used to detect and measure small electric currents. It works on the principle of the magnetic effect of current—a current-carrying coil experiences a force in a magnetic field, causing it to deflect.
Q44. The soft iron core with the coil wound on it is called:
The soft iron core with the coil wound on it is called the armature. It is the rotating part of an electric motor or generator. The armature rotates in the magnetic field, producing or using electromagnetic effects.
Q45. When the magnet is withdrawn, the current induced in the coil flows in:
When the magnet is withdrawn from the coil, the current induced flows in the opposite direction compared to when the magnet is moved towards the coil. This is due to Lenz’s law, which states that the induced current opposes the change causing it.
Q46. What happens to the magnetic field strength inside a current-carrying solenoid if the number of turns per unit length is increased?
The magnetic field strength inside a solenoid is directly proportional to the number of turns per unit length (B ∝ n). So, increasing the number of turns per unit length increases the magnetic field strength.
Q47. Which property of a charged particle can change in a magnetic field?
In a magnetic field, the direction of velocity of a charged particle can change, but its speed remains constant. The magnetic field exerts a force perpendicular to the velocity, changing the direction of motion. Charge and mass are invariant properties.
Q48. When the magnet moves towards the coil, the galvanometer shows:
When the magnet moves towards the coil, the galvanometer shows a momentary deflection. This is because the induced current exists only while the magnetic flux is changing. Once the magnet stops moving, the deflection returns to zero.
Q49. Brushes in an electric motor are used to:
Brushes in an electric motor are used to supply current to the rotating coil. They press against the commutator and allow current to flow from the external circuit to the coil, even as the coil rotates.
Q50. Commercial motors use electromagnets instead of:
Commercial motors use electromagnets instead of permanent magnets because electromagnets can produce much stronger magnetic fields. They are also more flexible—the field strength can be varied by changing the current in the electromagnet. This allows for better control of the motor’s performance.