NCERT Solutions for Chapter 13 Magnetic Effects of Electric Current Class 10 Science
Book Solutions1
Answer
The needle of a compass is a small magnet. That’s why when a compass needle is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle gets deflected.1
Answer
Magnetic field lines of a bar magnet emerge from the north pole and terminate at the south pole. Inside the magnet, the field lines emerge from the south pole and terminate at the north pole, as shown in the given figure.
2
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The properties of magnetic lines of force are as follows.→ Magnetic field lines emerge from the north pole.
→ They merge at the south pole.
→ The direction of field lines inside the magnet is from the south pole to the north pole.
→ Magnetic lines do not intersect with each other.
3
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The two magnetic field lines do not intersect each other because if they do it means at the point of intersect the compass needle is showing two different directions which is not possible.1
Answer
Inside the loop = Pierce inside the table
Outside the loop = Appear to emerge out from the table
For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.
2
Answer
3
Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current
(a) is zero
(b) decreases as we move towards its end
(c) increases as we move towards its end
(d) is the same at all points
Answer
(d) is the same at all points1
(a) mass
(b) speed
(c) velocity
(d) momentum
Answer
(c) velocity and (d) momentum2
(i) current in rod AB is increased,
(ii) a stronger horse-shoe magnet is used, and
(iii) length of the rod AB is increased?
Answer
The displacement of rod AB is increased due to magnetic force exerted on it, if :
(i) If the current in the rod is increased then rod will be deflected with greater force.
(ii) If a stronger horse-shoe magnet is used then also rod will be deflected with greater force due to the increase in magnetic field.
(iii) If the length of the rod AB is increased.
3
(a) towards south
(b) towards east
(c) downward
(d) upward
Answer
(d) upward1
Answer
Fleming's left hand rule states that if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field.2
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The principle of an electric motor is based on the magnetic effect of electric current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is according to the Fleming’s left-hand rule.3
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The split ring in the electric motor also known as a commutator reverses the direction of current flowing through the coil after every half rotation of the coil. Due to this the coil continues to rotate in the same direction.1
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The different ways to induce current in a coil are as follows:→ If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is induced in the coil.
→ If a magnet is moved relative to a coil, then an electric current is induced in the coil.
1
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Electric generator works on the principle of electromagnetic induction. Electricity is generated by rotating a coil inside magnetic field.2
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Some sources of direct current are cell, DC generator, etc.3
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AC generators, power plants, etc., produce alternating current.4
Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(b) one revolution
(c) half revolution
(d) one-fourth revolution
Answer
(c) half revolution1
Answer
Two safety measures commonly used in electric circuits and appliances are→ Electric Fuse: An electric fuse is connected in series it protects the circuit from overloading and prevents it from short circuiting.
→ Proper earthing of all electric circuit in which any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.
2
Answer
Current drawn by the electric oven can be obtained by the expression,
P = VI
Where,
Current = I
Power of the oven, P = 2 kW = 2000 W
Voltage supplied, V = 220 V
Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.
3
Answer
The precautions that should be taken to avoid the overloading of domestic circuits are as follows:→ Too many appliances should not be connected to a single socket.
→ Too many appliances should not be used at the same time.
→ Faulty appliances should not be connected in the circuit.
→ Fuse should be connected in the circuit.
1
(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
Answer
(d) The field consists of concentric circles centred on the wire2
(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
Answer
(c) producing induced current in a coil due to relative motion between a magnet and the coil3
(a) generator
(b) galvanometer
(c) ammeter
(d) motor
Answer
(a) generator4
(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.
Answer
(d) AC generator has slip rings while the DC generator has a commutator.5
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously
Answer
(c) increases heavily6
Answer
(a) False
(c) True
(d) False
7
Answer
Three sources of magnetic fields are as follows:→ Current-carrying conductors
→ Permanent magnets
→ Electromagnets
8
Answer
A solenoid is a long coil of circular loops of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is allowed to flow through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current-carrying solenoid is shown in the following figure.
In the above figure, when the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves as a north pole and the other end behaves as a south pole.
9
Answer
The force experienced by a current-currying conductor is the maximum when the direction of current is perpendicular to the direction of the magnetic field.10
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The direction of the magnetic field is vertically downwards. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from 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.11
Answer
After half a rotation, the position of MN and ST interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. Hence, the direction of current in the coil MNST gets reversed.
The current flows through the coil in the direction TSNM. The reversal of current through the coil MNST repeats after each half rotation. As a result, the coil rotates unidirectional.
12
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Some devices in which electric motors are Water pumps, Electric fans, Electric mixers and Washing machines.13
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(i) The needle of the galvanometer shows a momentary deflection in a particular direction.(ii) The needle of the galvanometer shows a momentarily in the opposite direction.
(iii) The needle of the galvanometer shows no deflection.
14
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Two circular coils A and B are placed close to each other. When the current in coil A is changed, the magnetic field associated with it also changes. As a result, the magnetic field around coil B also changes. This change in magnetic field lines around coil B induces an electric current in it. This is called electromagnetic induction.15
Answer
(i) Maxwell's right hand thumb rule(ii) Fleming's left hand rule
(iii) Fleming's right hand rule
16
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Principle: An electric generator works on the principle of electromagnetic induction phenomenon. According to it, whenever a coil is rotated between the poles of a magnet, an induced current is set up in the coil, whose direction is given by Fleming’s right hand rule.
Working: Let in the beginning, as shown in Fig. brushes B1 and B2 are kept pressed separately on rings R1 and R2 respectively. Let the axle attached to the rings is rotated such that arm AB of the coil moves up and arm CD moves down in the magnetic field. Due to rotation of arms AB and CD induced currents are set up in them. As per Fleming’s right hand rule induced currents in these arms are along the directions AB and CD. Thus an induced current flows along ABCD and current in the external circuit flows from B2 to B1.
After half a rotation, arm AB starts moving down and the arm CD upward. Therefore, directions of induced currents in these arms change. Thus net induced current now becomes in the direction DCBA. In the external circuit now current flows from B1 to B2. Thus after every half rotation current changes its direction and an alternating current is obtained from the generator.
Function of Brushes: Brushes are kept pressed on the two slip rings separately. Outer ends of the brushes are connected to the galvanometer (or the external load). Thus brushes help in transferring current from the coil ABCD to the external circuit.
17
Answer
If the insulation of the wires used in the circuit is damaged or the appliance used is faulty due to which the live wire and the neutral wire comes in direct contact as a result current in the circuit rises and the short circuit occurs.18
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The metallic body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary.