Objective

Question-1. Who are you calling a magnet? How many types of magnets are there, and what are the uses of magnets?

Ans- Magnet → A substance that attracts pieces of iron, steel, cobalt, and nickel towards itself is called a magnet.

There are two types of magnets.

• natural magnet

• artificial magnet

Uses → Magnets are used in radios, refrigerators, computers, children's toys.

Question-2. What is a magnetic field called?

Ans- The area around a magnet in which the effect of the forces of attraction and repulsion can be felt is called magnetic field.

Question-3. Draw magnetic lines around a bar magnet.

Ans-

Question-4. List the properties of magnetic field lines.

Ans- Magnetic field lines have the following properties.

• Magnetic force lines are closed curves.

• Two magnetic field lines never intersect each other.

• Where the magnetic field lines are close to each other, the magnetic field is stronger.

Question-5. Why do two magnetic field lines not intersect each other?

Ans- If two magnetic field lines intersect at any one point, then two different directions will be obtained at that point, which is not possible. Therefore two magnetic field lines do not intersect each other.

Question-6. Why does the compass needle get deflected when brought near a magnet?

Ans- The needle of a compass is also a small magnet. When it is brought near a magnet, the compass needle gets deflected due to the force of attraction or repulsion.

Question-7. The magnetic field in a given region is uniform. Draw a diagram to represent it.

Ans-

Question-8. What is the magnetic effect of electric current called?

Ans- When an electric current flows through a conducting wire, a magnetic field is produced around it, so this effect is called the magnetic effect of the current. This fact was discovered by Oersted in 1820 AD.

Question-9. What is a solenoid called?

Ans- When a coil of a conducting wire is wrapped over a dielectric material, such an arrangement is called a solenoid. One end of the solenoid acts as the magnetic north pole and the other end as the magnetic south pole.

Question-10. What is an electromagnet called?

Ans- When a soft iron rod is placed inside the solenoid, the rod gets magnetized due to the current, such a rod is called core. Such a core of soft iron is called an electromagnet.

Question-11. What is the use of electromagnet?

Ans- Following are the uses of electromagnet-

• An electromagnet is used in cranes, which makes it easy to lift heavy pieces of iron.

• Electromagnets are used in electric bells, microphones, televisions, loudspeakers, etc.

Question-12. What is the difference between electromagnet (temporary magnet) and permanent magnet?

Ans- Electromagnet

• An electromagnet is a temporary magnet.

• The force of attraction of an electromagnet is strong.

• The strength of an electromagnet depends on the number of turns.

Permanent Magnet

• A bar magnet is a permanent magnet.

• The force of attraction of a permanent magnet is weak.

• The strength of a permanent magnet is fixed.

Question-13. What is Fleming's left-hand rule?

Ans- According to Fleming's left-hand rule – If the index, middle, and thumb of the left hand are stretched perpendicular to each other in such a way that if the forefinger shows the direction of the magnetic field and the middle finger shows the direction of the current, then the thumb will represent the direction of force acting on the current-carrying conductor.

Question-14. What is called the Lorenz force?

Ans- When a conductor is placed in a magnetic field, a force is exerted on the moving electrons, which is called the Lorenz force. These forces are perpendicular to the velocity of the electrons and the directions of the magnetic field.

Question-15. On what does the force acting on a current-carrying conductor in a magnetic field depend?

Ans- The force acting on a current carrying conductor in a magnetic field depends on the following factors.

• on the strength of the magnetic field

• on the strength of electric current

• on the length of the driver

Question-16. What is Magnetic Resonance Imagery (MRI)?

Ans- One such special technique, using which the magnetic field inside the body becomes the basis for obtaining the images of different parts of the body, is called magnetic resonance imaging.

Question-17. What is electric motor? what is it used for?

Ans- An electric motor is a device that converts electrical energy into mechanical energy. It is used in the manufacture of electric clothes, washing machines, refrigerators etc.

Question-18. What is electromagnetic induction called?

Ans- The phenomenon of producing current in a conductor due to a changing magnetic field (flux) is called electromagnetic induction. Electromagnetic induction was discovered by Faraday in 1831.

Question-19. What is magnetic flux called?

Ans- The product of the plane surface normal component of the magnetic field on a plane surface and the surface area is called magnetic flux. The SI unit of magnetic flux is waver.

Question-20. What is Fleming's right-hand rule?

Ans- According to Fleming's right-hand rule: - If the index finger of the right hand, the middle finger, and the thumb are spread perpendicular to each other in such a way that the same index finger represents the direction of the magnetic field, the thumb indicates the direction of motion of the conductor, then the middle finger will represent the direction of the induced current in the conductor.

Question-21. What is Faraday's law of electromagnetic induction and Lenz's law?

Ans- Faraday's Law of Electromagnetic Induction: According to Faraday's law of electromagnetic induction, the result of an induced emf 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.

Lenz's law:- Whenever a current is produced in a circuit by electromagnetic induction, its direction is such that it opposes the one from which it is generated. This is called Lenz's law.

Question-22. What is an electric generator? Describe its structure and mechanism?

Ans- Electric generator:- Electric generator (dynamo) is a device by which mechanical energy is converted into electrical energy. It works on the principle of electromagnetic induction.

Texture:- The electric generator (dynamo) has a powerful cord magnet. Which is called a field magnet. Between the poles of a field magnet, there is a coil called armature rotating on a horizontal axis. The armature consists of several turns of the coil, which are wrapped on soft iron strips. Let's call it the core of the armature. The ends of the armature wire are covered with brass rings and the carbon strips lightly touch with these rings. These leaves are called brushes. The circuit is attached to the screws in these brushes.

Methodology:- When the armature is rotated, the magnetic field (flux) inside the coil changes every moment. In this, the direction of current changes in each half cycle of rotation i.e. in one-half cycle the current reaches from zero to medium, and in the second time the current decreases from medium to zero. Thus in one rotation, the current in one direction attains zero to medium and medium to zero again zero to medium and medium to zero value in the opposite direction. Due to the variable value of current, this current is called alternating current, and this type of dynamo is called alternating current dynamo ie AC dynamo.

Question-23. What is the advantage of alternating current?

Ans- The following are the advantages of alternating current—

• Alternating current can be sent very far by increasing its electromotive force with the help of a transformer.

• Due to the high capacity of alternating current, it is used in large factories.

• A 6 volt light can also be lit by reducing the electromotive force of the alternating current.

• Alternating current can be controlled with minimal energy loss.

Question-24. What are the disadvantages of alternating current?

Ans- Alternating current has the following disadvantages.

• Electric coatings and batteries cannot be charged with alternating current.

• Alternating current cannot be dissipated in the conducting cell.

• Alternating current is very dangerous.

• Alternating current cannot be used in an electromagnet.

Question-25. What is the power distribution system called?

Ans- The arrangement of electricity supply from the power generation center to the homes of the consumers by the arrangement of special type of wires is called power distribution system.

Question-26. What are the live wire (hot wire) and neutral wire (cold wire) called?

Ans- Two wires are used to install electrical circuits in homes. One of them has potential 220 V and frequency 50 H2 and the other wire is in contact with earth. This 220 V wire is called the live wire and the wire in contact with the earth is called neutral.

Question-27. Describe the principle and working of electric motor. What is the significance of the dividing ring in an electric motor?

Ans-

Electric motor:- An electric motor is a device that converts electrical energy into mechanical energy. It is used in the manufacture of electric fans, washing machines, refrigerators, etc.

Texture:- The electric motor has a coil magnet called a field magnet, between the pole segments of the magnet, is a coil of copper wire wrapped on a core made of soft iron plates, whose number of turns is very high. It is called the armature of the motor and is connected to the broken brass rings by the armature. The carbon brushes keep touching these rings.

Methodology:- When an electric current is passed through the armature, the two arms of the armature which are perpendicular to the direction of the magnetic field experience a force according to Fleming's left-hand law. These forces are equal in value but opposite in direction, hence these forces - make a pair due to which the armature is rotated, after half the rotation, the positions of the rings are exchanged and the armature septum force couple keeps the armature continuously rotating in the same direction, hence it is also called DC motor.

Question-28. Describe and verify electromagnetic induction. That is, describe Faraday's experiment.

Ans-

Electromagnetic induction:- The important relationship between electricity and magnetism was discovered by Faraday in 1831 that he proved by his experiment that if a magnet (bar magnet) is brought near a closed coil or that magnet is moved away from that coil So in both the cases current flows in the coil, this current flows as long as the magnet remains in motion, thus the electromotive force and the current flow in the conductor as long as the magnet remains in motion, thus the electromotive force in the conductor And electric current is induced which is also called electromagnetic induction.

Verification:- To show this, we will first take a hollow cylinder and wrap a coil of wire with many turns over that cylinder. After this, we will connect a galvanometer to the wire. Now we take a bar magnet and bring it fast near the coil, we see that the needle of the galvanometer gets deflected in a particular direction (say to the right) again when we take it away from the coil of the bar magnet, then We see that the needle of the galvanometer gets deflected to the left, in this way the magnetic field due to the bar magnet increases when brought closer and decreases when taken away and when both the coil and the magnet are stabilized, the needle of the galvanometer There is no deflection of any kind.

Therefore, it is clear in this way that the induced electromotive force is generated by the motion of the magnet relative to the coil, due to which an electric current is generated in the circuit. This phenomenon of electric current induced by the electromotive force is called electromagnetic induction.