1. Part 2 By:- Nivesh krishna Class X-D

2. Electric current flowing a conductor produces a magnetic field. The field so produced exerts a force on magnet placed in the vicinity of the conductor Marie Ampere suggested that the magnet must also exert an equal and opposite force on the current carrying conductor. 3. The direction of the force is also reverse when the direction of the current through the conductor is reversed. The video suggest that the direction of the force on the conductor depends upon the direction of current and the direction of magnetic field. When the direction of the current is perpendicular to the magnetic field we can use a simple rule to find out the direction of the force acting on the conductor. The simple rule is FLEMINGs LEFT HAND RULE 4. An electric motor is a rotating device that converts electrical energy to mechanical energy. Principle of electric motor 5. A device that reverses the direction of the flow of current through a circuit is called a commutator. Electric motors Is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, etc. 6. o Now let us imagine a situation in which a conductor is moving o inside a magnetic field or a magnetic field is changing around a fixed conductor. What will happen? o This was first studied by English physicist Michael Faraday. In 1831, Faraday made an important breakthrough by discovering how a moving magnet can be used to generate electric currents. 7. A galvanometer is an instrument that can detect the presence of a current in a circuit. The pointer remains at zero (the Centre of the scale) for zero current flowing through it. It can deflect either to the left or to the right of the zero mark depending on the direction of current. we conclude that a potential difference is induced in the coil-2 whenever the electric current through the coil1 is changing (starting or stopping). Coil-1 is called the primary coil and coil-2 is called the secondary coil. As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it. This process, by which a changing magnetic field in a conductor induces a current in another conductor, Is called electromagnetic induction. 8. The induced current is found to be the highest when the direction of motion of the coil is at right angles to the magnetic field. In this situation, we can use a Simple rule to know the direction of the induced current. Stretch the thumb, forefinger and middle finger of right hand so that they are perpendicular to each other, as shown in the figure. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of conductor, then the middle finger will show the direction of induced current. This simple rule is called Flemings right-hand rule. 9. Based on the phenomenon of electromagnetic induction, the experiments studied above generate induced current, which is usually very small. This principle is also employed to produce large currents for use in homes and industry. In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity. 10. If there are larger numbers of turns in the coil, the current generated in each turn adds up to give a large current through the coil. The directions of the induced currents in both the arms change, giving rise to the net induced current in the direction CBA. The current in the external circuit now flows from B1 every half rotation the polarity of the current in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current (abbreviated as AC). This device is called an AC generator. 11. To get a direct current (DC, which does not change its direction with time), a split-ring type commutator must be used. With this arrangement, one brush is at all times in contact with the arm moving up in the field, while the other is in contact with the arm moving down. Thus a unidirectional current is produced. The generator is thus called a DC generator. 12. The difference between the direct and alternating currents is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically. Most power stations constructed these days produce AC. In India, the AC changes direction after every 1/100 second, that is, the frequency of AC is 50 Hz. An important advantage of AC over DC is that electric power can be transmitted over long distances without much loss of energy. 13. In our homes, we receive supply of electric power through a main supply (also called mains), either supported through overhead electric poles or by underground cables. One of the wires in this supply, usually with red insulation cover, is called live wire (or positive). Another wire, with black insulation, is called neutral wire (or negative). In our country, the potential difference between the two is 220 V. At the meter-board in the house, these wires pass into an electricity meter through a main fuse. Through the main switch they are connected to the line wires in the house. These wires supply electricity to separate circuits within the house. Often, two separate circuits are used, one of 15 A current rating for appliances with higher power ratings such as geysers, air coolers, etc. 14. The other circuit is of 5 A current rating for bulbs, fans, etc. The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house. This is used as a safety measure, especially for those appliances that have a metallic body, for example, electric press, toaster, table fan, refrigerator, etc. 15. The above figure gives a schematic diagram of one of the common domestic circuits. In each separate circuit, different appliances can be connected across the live and neutral wires. Each appliance has a separate switch to ON/OFF the flow of current through it. In order that each appliance has equal potential difference, they are connected parallel to each other. 16. 1. In a plane perpendicular to magnetic meridian the dip needle will: (a) be horizontal (b) be vertical (c) dip at angle equal to the angle of dip at the place (d) point in any direction 2. Two long straight wires are set parallel to each other. Each carries a current I in the same direction and the separation between them is 2. The intensity of the magnetic field at midway between the wires is: (a) zero (b) o r (c) o I/ r (d) 2 o I / r 3. To estimate magnetic flux density B at the centre of a long solenoid the following measurements are carried out: P. The volume of the solenoid. Q. The diameter of each turn of the solenoid. R. the number of turns per unit length of the solenoid. S. The current through the solenoid B is dependent on: (a) Only R (b) R and S (c) Q, R and S (d) Q and S Answer Keys: 1. (b) 2. (a) 3. (b) 17. 4. Consider the statements: A. Moving charges do not produce any electric filed. B. Stationary charges do not produce any magnetic field. Of the two statement. (a) A is false (b) B is false (c) Both are false (d) both are true 5. A beta-particle of mass m and an a particle of mass M are injected perpendicularly in a uniform magnetic field B. Both particles are found to move on circular paths of the same radius. The ratio of the kinetic energy of the -particle to that of the -particle is : (a) 4 (M/m)3 (b) (m/M)3/4 (c) 4 M/m (d) m/4m 6. Consider the statements concerning the Magnetic field B at the centre of a circular coil due to a current I flowing in the coil. X. B is independent of r Y. B is proportional to he circumference an inversely proportional to r: Of the two statements. (a) both are false (b) x is false (c) Y is false (d) both are true Answer Keys: 4. (a) 5. (d) 6. (a) 18. 7. A uniform circular wire of resistance R and of radius r has two points P and Q on its, circumference. Path PQ=r/2 P and Q connected to a distant ideal battery of emf V volts through straight wires of negligible resistance pointing towards the centre of the circle. The magnitude of magnetic field at the centre of the circular wire is : (a) zero (b) 2oV/3Rr (c) 2oV/Rr (d) 2V/Rr 8. A neutrino an electron and a neutron move along a uniform magnetic field. The correct inference is: (a) only the path of the electron will be affected (b) only the paths of the neutrino and the neutron will be affected (c) the speed of electron will change [] (d) the paths of none of the particles will be affected 9. A particle of charge q moving with a velocity v perpendicular to a uniform magnetic field B in a circular path of radius r has a momentum. (a) qvB (b) qBr (c) qBr2 (d) q2Br 10. A straight conductor in the plane of the paper and carrying a current in the Y- direction is subjected to a uniform magnetic field in the + x-direction. The wire tends to move: (a) toward x direction (b) toward + x direction (c) into the paper away from the reader (d) out of the paper towards the reader Answer Keys: 7. (a) 8. (d) 9. (b) 10. (d) 19. Thank You By:- Nivesh Krishna Class X-D