Title CHAPTER 13 MAGNETIC EFFECTS OF ELECTRIC CURRENT.doc ✅

3 CHAPTER 2 CBSE X PHYSICS MAGNETIC EFFECTS OF CURRENT Ans. To avoid overloading, we should not connect too many appliances to a single socket. Q22. Which of the following correctly describes the magnetic field near a long straight wire? (a) The field consists of straight lines perpendicular to the wire. (b) The field consists of straight lines parallel to the wire. (c) The field consists of radial lines originating from the wire. (d) The field consists of concentric circles centred on the wire. Ans. The correct option is (d). Q23. The phenomena, of electromagnetic induction is (a) the process of charging a body, (b) the process of generating magnetic field due to a current passing through a coil, (c) producing induced current in a coil due to relative motion between a magnet and the coil, (d) the process of rotating a coil of an electric motor. Ans. The correct option is (c). Q22. The device used for producing electric current is called a (a) generator (b) galvanometer (c) ammeter (d) motor. Ans. The correct option is (a). Q25. The essential difference between an ac generator and a dc generator is that: (a) ac generator has an electromagnet while a dc generator has permanent magnet, (b) dc generator will generate a higher voltage, (c) ac generator will generate a higher voltage, (d) ac generator has slip rings while the dc generator has a commutator. Ans. The correct option is (d). Q26. At the time of short-circuit, the current in the circuit (a) reduces substantially (b) does not change (c) increases heavily (d) varies continuously. Ans. The correct option is (c). Q27. State whether the following statements are true or false. (Page 220) (a) An electric motor converts mechanical energy into electrical energy. (b) An electric generator works on the principle of electromagnetic induction. (c) The field at the centre of a long circular coil carrying current will be parallel straight lines. (d) A wire with a green insulation is usually the live wire. Ans. (a) False. An electric motor converts electric energy into mechanical energy. (b) True. (c) True. (d) False. A wire with a green insulation is usually the earth wire. Q28. List three sources of magnetic fields. Ans. (i) Natural and artificial magnets (ii) Electromagnets (iii) A conductor, a coil and a solenoid carrying current Q29. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current carrying solenoid with a help of bar magnet? Explain. Ans. A current carrying solenoid behaves like a bar magnet and the polarities of its ends depend upon the direction of current flowing through it. In order to determine the polarities of its ends, place it in a brass hook and suspend it with a long thread so that it moves freely. Bring North Pole of a bar magnet near one of its ends. In case the solenoid moves towards the bar magnet that end of the solenoid is a south pole and in case the solenoid moves away from the magnet, that end of the solenoid is its north pole. Similarly we can determine the polarity of the other end of the solenoid. Q30. When is the force experienced by a current- carrying conductor placed in a magnetic field is largest? Ans. The force experienced by a current-carrying conductor placed in a magnetic field is the largest when the direction of the current is at right angles to the direction of the magnetic field. Q31. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field? Ans. The direction of conventional current is opposite to the direction of electron beam. Therefore the current is towards the back wall. Since the beam is deflected to the right side, the force (F) acting on the beam is towards this side. Applying Fleming’s left rule, it is found that magnetic field (B) is acting vertically downwards (i.e., perpendicular to the plane of the paper and directed inwards). Q32. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split-ring in an electric motor? Ans. Refer to Art. 2.11, fig2.24. Split-ring in an electric motor takes the current from the battery and passes it on to the coil through the brushes after reversing its direction after every half revolution. The reversal of current in the coil reverses the direction of forces acting on the sides of the loop.