Objective

Question-2. What is the black ore of iron (Fe₃O₄) called?

Ans- magnetite

Question-3. Which attracts pieces of iron or other magnetic materials towards them. What is such a magnet-stone called?

Ans- natural magnet

Question-4. Which is the main magnet in an artificial magnet?

Ans- rod magnet

Question-5. In which direction does the magnet on the compass needle point?

Ans- north-south direction

Question-6. What is the point pointing north called?

Ans- North Pole

Question-7. What is the point pointing south called?

Ans- south pole

Question-8. What happens between similar poles of a magnet?

Ans- repulsion

Question-9. What happens between unequal poles of a magnet?

Ans- Attraction

Question-10. What are magnets used for?

Ans- In radios, tape, refrigerators, computers, children's toys, etc.

Question-11. The area around a magnet in which the effects of the forces of attraction and repulsion can be felt is called

Ans- Magnetic Field

Question-12. There are magnetic lines of force.

Ans- closed curve

Question-13. Where magnetic field lines are very close to each other, there is a magnetic field.

Ans- stronger

Question-14. Two magnetic field lines never intersect.

Ans- intersection

Question-15. When a current flows through a conducting wire, a magnetic field is also produced around it, what is this fact called?

Ans- magnetic effect of current

Question-16. Who discovered the magnetic effect of electric current?

Ans- Oersted (in 1820 AD)

Question-17. Oersted's experiment shows the relationship between—

Ans- the relation between electricity and magnetism

Question-18. What is the experiment that shows the effect of current on a magnet called?

Ans- Oersted's experiment

Question-19. Whose direction changes when the direction of the current changes?

Ans- of magnetic field

Question-20. If the current carrying wire is held in the fist of the right hand in such a way that the thumb will indicate the direction of the current, and the other fingers will indicate the direction of the lines of force of the magnetic field, it is known as

Ans- Maxwell's right hand rule

Question-21. What is another name for Maxwell's law?

Ans- corkscrew rule

Question-22. When a coil of a conducting wire is wrapped over a dielectric material, then such an arrangement is called?

Ans- solenoid

Question-23. When a soft iron rod is placed inside the solenoid, the rod gets magnetized due to the current, so what is such a rod called?

Ans- core

Question-24. What is a soft iron core called?

Ans- electromagnet

Question-25. There is an electromagnet.

Ans- floating magnet

Question-26. Rods are magnets.

Ans- permanent magnet

Question-27. The force of attraction of an electromagnet is.

Ans- strong (too much)

Question-28. A permanent magnet has a force of attraction.

Ans- Weak

Question-29. On what does the strength of an electromagnet depend?

Ans- on the number of furrows

Question-30. Permanent magnet has power.

Ans- Fixed

Question-31. Electromagnet is used.

Ans- In crane, Electric bell, Microphone, Television, Loud speaker

Question-32. What is used in place of soft iron to make permanent magnets?

Ans- steel rod

Question-33. If the forefinger, middle finger and thumb of the left hand are spread perpendicular to each other in such a way that the forefinger and middle finger will represent the direction of the magnetic field and the thumb will represent the direction of the force acting on the current carrying conductor, it is called which law?

Ans- Fleming's left hand rule

Question-34. What is the cause of electric current in a conductor?

Ans- free flow of electrons

Question-35. What is the force on a moving electron when a conductor is placed in a magnetic field?

Ans- Lorenz force

Question-36. The force (F) on the current carrying conductor is equal to the length (l) of the conductor.

Ans- directly proportional

Question-37. The force (F) on a current-carrying conductor is equal to the strength (i) of the current?

Ans- directly proportional

Question-38. When a current carrying conductor is placed parallel to the magnetic field, no experience is experienced.

Ans- of force

Question-39. The SI unit of magnetic field is

Ans- tesla

Question-40. An experiment that demonstrates the effect of a magnetic field on an electric current is called—

Ans- Faraday's experiment

Question-41. What is the action of electric motor based on?

Ans- on the magnetic effect of electric current

Question-42. A special technique by which magnetic fields within the body become the basis for obtaining images of different parts of the body, is this technique called?

Ans- Magnetic Resonance Imagery (MRI)

Question-43. What is the full form of MRI?

Ans- Magnetic Resonance Imaging

Question-44. What is a device that converts electrical energy into mechanical energy called?

Ans- electric motor

Question-45. Electric motor is used—

Ans- In electric fans, washing machines and refrigerators

Question-46. There is a cord magnet in an electric motor, what is it called?

Ans- field magnet

Question-47. What is the coil of copper wire wrapped on a core made of soft iron plates between the poles of a magnet called?

Ans- motor armature

Question-48. What are the ends of the armature connected to?

Ans- from broken rings of brass

Question-49. Who keeps touching the broken rings of brass?

Ans- carbon brushes

Question-50. If a blade is placed on the axis of the armature of an electric motor, what will become of an electric motor?

Ans- electric fan

Question-51. The phenomenon of generation of current in a conductor due to a changing magnetic field (flux) is called?

Ans- electromagnetic induction

Question-52. Who discovered electromagnetic induction?

Ans- Faraday (in 1831 AD)

Question-53. If the forefinger, middle finger and thumb of the right hand are stretched perpendicular to each other in such a way that the forefinger and thumb will represent the direction of the magnetic field and the thumb will represent the direction of motion of the conductor and the middle finger will represent the direction of the induced current in the conductor. What is this rule called?

Ans- Fleming's right-hand rule

Question-54. What is the product of the normal component of the magnetic field on a plane surface and the product of the surface area called?

Ans- magnetic flux

Question-55. What is the SI unit of magnetic flux?

Ans- Weber

Question-56. What is the magnetic flux denoted by?

Ans- Φ (fie)

Question-57. The magnitude of the induced electric carrying force in a circuit is proportional to the rate of change of the magnetic force lines passing through that circuit and the number of turns in the circuit.

Ans- law of electromagnetic induction

Question-58. When a current is produced in a circuit by an electromagnetic induction, its direction is such that it opposes the one from which it is produced. What is this rule called?

Ans- lange's law

Question-59. Which device converts mechanical energy into electrical energy?

Ans- Electric Generator (by Dynamo)

Question-60. On what principle does an electric generator (dynamo) work?

Ans- on the principle of electromagnetic induction

Question-62. What is a dynamo that receives alternating current called?

Ans- A.C. Dynamo

Question-63.Such an electric current whose magnitude is constant or variable but the direction of flow is same in the conductor is called.

Ans- Direct Current (D.C.)

Question-64. Such an electric current whose direction keeps changing in a particular time interval is called?

Ans- Alternating Current (A.C.)

Question-65. Direct current has a frequency.

Ans- Zero (0)

Question-66. What is the frequency of alternating current for domestic use in India?

Ans- 50 Hz

Question-67. Alternating current (A.C.) flows.

Ans- on the surface of the driver

Question-68. Direct current (D.C.) flows.

Ans- from inside the driver

Question-69. Alternating current cannot be stored.

Ans- in the accumulator cell

Question-70. Alternating current (A.C.) is not used to make what?

Ans- in electromagnet

Question-71.What is the insulating wire of red color, black color and green color called?

Ans-

Red Insulated Wire → Live or Positive Wire

Black Insulated Wire → Neutral or Negative Wire

Green Insulated Wire → Earthing Wire

Question-71. What are the lines of 15 A (ampere) and 5 A (ampere) called?

Ans-

15 A (Ampere) → Power Line

5 A (ampere) → domestic line

Question-72. Switches in domestic circuits are always connected with live wire.

Ans- in order

Question-73. Which are the devices which reverse the direction of flow of current in a circuit?

Ans- Direction converter

Question-74. By what can the voltage of alternating current be increased or decreased?

Ans- by transformer

Question-75. Which are the devices which produce direct current?

Ans- Alternating current generator

Question-76. How many types of dynamo are there?

Ans- Two (alternating current dynamo and direct current dynamo)

Question-77. What does an alternating current dynamo produce?

Ans- Alternating current

Question-78. What does a direct current dynamo produce?

Ans- Direct current

Question-79. What is used to make permanent magnets?

Ans- Hard steel and alloy

Question-80. What is used to make temporary magnets?

Ans- Soft iron

Question-81. The electricity supplied to our homes is-

Ans- Alternating current at 220 V

Question-82. The magnetic field inside an electric current-carrying straight long solenoid—

Ans- are equal at all points.

Question-83. In the direction of alternating current conductor-

Ans- are reversed periodically.

Question-84. Which material is used to make an electromagnet?

Ans- Soft iron

Question-85. What should be the minimum speed of wind in a wind power generator?

Ans- 15 km/h

Question-86. How is energy converted in a dynamo?

Ans- conversion of mechanical energy into electrical energy

Question-87. How many poles does a magnet have?

Ans- Two (North Pole and South Pole)

Question-88. After how many revolutions does the direction of the induced current in the coil change?

Ans- half

Question-89. What are the directions of the magnetic field lines inside a bar magnet?

Ans- North Pole to South Pole

Question-90. In which device does the dividing ring act as a change of direction?

Ans- Electric Generator (Dynamo)

Question-91. What energy do hydroelectric plants convert into electrical energy?

Ans- Potential energy

Question-92. In which state Narora Nuclear Power Plant is located?

Ans- In Uttar Pradesh

Question-93. Which of the following are helpful in determining the direction of the magnetic field produced by a current carrying wire?

Ans- Right hand thumb rule

Question-94. In Fleming's left hand rule, the index finger of the left hand indicates—

Ans- Magnetic field direction

Question-95. How many wires are in home wiring?

Ans- Three (live wire, neutral wire and ground wire)

Question-96. What is an electric fuse connected to in an electric circuit?

Ans- in live (hot) wire

Question-97. From which pole do magnetic field lines originate?

Ans- from the north pole

Question-98. Current is flowing in a circular coil. Where will the magnetic field intensity due to the coil be maximum?

Ans- at the center

Question-99. What is the unit of magnetic field intensity?

Ans- Newton/Ampere-meter

Question-100. What is the formula to find the resistance of a coil?

Ans- R = V/I

प्रश्न-101. When brought near the magnet, the compass becomes needle.

उत्तर- deflected