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Why does a compass needle get deflected when brought near a bar magnet?
A compass needle is a small bar magnet. When it is brought closer to a bar magnet, its magnetic field lines interact with the bar magnet. Therefore, a compass needle shows a deflection when brought near the bar magnet.
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Which of the following property of a proton can change while it moves freely in a magnetic field? (a) mass (b) speed (c) velocity (d) momentum
(c) and (d) When a proton enters a magnetic field area, it experiences a magnetic force. As a result of the force, the path of the proton becomes circular. Therefore, its velocity and momentum change.
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Explain different ways to induce a current in a coil.
The different ways to induce a current in a coil are as follows: (a) An electric current is induced in the coil, if a coil is moved rapidly between the two poles of a horse-shoe magnet. (b) And if a magnet is moved relative to a coil,
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Choose the correct option. A rectangular coil of copper wire is rotated in a magnetic field. The direction of the induced current changes once in each (a) two revolutions (b) one revolution (c) half revolution (d) one-fourth revolution
(c) When a rectangular coil of copper is rotated in a magnetic field, the direction of the induced current in the coil changes once in each half revolution
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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
(d) The magnetic field lines, produced around a straight current-carrying conductor, are concentric circles. Their centres lie on the wire.
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The device used for producing electric current is called a (a) generator (b) galvanometer (c) ammeter (d) motor
(a) An electric current is produced by an electric generator. It converts mechanical energy into electricity.
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How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
A solenoid is a long coil of insulated copper wire circular loops. When a current flows through it, magnetic field lines are produced around the solenoid. The magnetic field produced by it is similar to a bar magnet. When the north pole of a bar magnet is brought close to the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel they are like poles that is the end connected to the -veined is the north pole. Therefore, the positive end of the solenoid is the south pole.
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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 magnetic field?
The direction of magnetic field is given by Fleming’s left hand rule. Magnetic field inside the chamber will be perpendicular to the direction of current (opposite to the direction of electron) and direction of deflection/force i.e., either upward or downward. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from the back wall to the front wall. The direction of magnetic force is rightward. Hence, using Fleming’s left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.
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Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
An electric generator converts mechanical energy into electrical energy. The following figure shows an electric generator. It includes a rotating rectangular coil ABCD placed between the two poles of a permanent magnet. The ends of this coil are connected to the two rings R1 and R2 whose inner side are made insulated. The two conducting stationary brushes B1 and B2 are kept pressed separately on the rings R1 and R2. These rings are internally attached to an axle. The axle may be mechanically rotated from outside to the coil inside the magnetic field. Outer ends of these brushes are connected to the galvanometer to show the flow of current in the external circuit. When the axle connected to the two rings is rotated in such a way that the arm AB moves up in the magnetic field produced by the permanent magnet. Suppose the coil ABCD is rotated clockwise. By applying Fleming’s right-hand rule, the induced currents are generated in these arms along the directions AB and CD. Hence, an induced current flows in the direction ABCD. If there are large numbers of turns in the coil, the current produced in each turn adds up to give a large current through the coil which means the current flows from B2 to B1. After the half rotation, arm CD moves up and AB moves down. Due to this, the directions of the induced currents in both the arms change, which increases the net induced current in the direction DCBA. Now, the current in the external circuit flows from B1 to B2. Therefore, after each rotation the polarity of the current in the respective arm changes. Such a current that changes direction after equal intervals of time is called an alternating current. So, this device is called an AC generator. In order to get a direct current, a split-ring type commutator should be used. With this arrangement, one brush is at all times in contact with the arm moves up, while the other moves down. Therefore, a unidirectional current is generated. Hence, the generator is called a DC generator.
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When does an electric short circuit occur?
An electric short circuit occurs: 1. When the resistance of an electric circuit becomes very low, and the current flowing through the circuit becomes very high. This is caused by connecting too many devices to a single socket or connecting high power rating appliances to the light circuits. 2. When the insulation of live and neutral wires undergoes wear and tear and then touches each other, the current flowing in the circuit increases abruptly.
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