# Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Class 10 Science Chapter 13 Magnetic Effects of Electric Current The answer to each chapter is provided in the list so that you can easily browse throughout different chapters NCERT Class 10 Science Chapter 13 Magnetic Effects of Electric Current and select need one.

### Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 10 Science Chapter 13 Magnetic Effects of Electric Current Solutions for All Subjects, You can practice these here…

EXERCISES

Q.1. 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 :- ( d ) The field consists of concentric circles centred on the wire.

Q.2. The phenomenon 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 :- ( c ) Producing induced current in a coil due to relative motion between a magnet and the coil.

Q.3. The device used for producing electric current is called a

( a ) Generator.

( b ) Galvanometer.

( c ) Ammeter.

( d ) Motor.

Ans :- ( a ) Generator.

Q.4. The essential difference between 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 connector.

Ans :- ( d ) AC generator has slip rings while the DC generator has a connector.

Q.5. At the time of short circuit, the current in the circuit.

( a ) Reduces substantially.

( b ) Does not change.

( c ) Increases heavily.

( d ) Vary continuously.

Ans :- ( c ) Increases heavily.

Q.6. State whether the following statement are true or false-

( 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 of an electric supply.

Ans :- ( a ) False.

( b ) True.

( c ) True.

( d ) False.

Q.7. List two methods of producing magnetic fields.

Ans :- ( i ) Magnetic field around current carrying conductor.

( ii ) Magnetic field around a current carrying solenoid.

Q.8. 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.

Ans :- The pattern of the field of a solenoid is same with the magnetic field around a bar magnet. One end of the solenoid behaves as a magnetic north pole, while the other behaves as the south pole. The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid, That is, the field is uniform inside the solenoid.

A strong magnetic field produced inside a solenoid can be used to magnetise a piece of magnetic material, like soft iron, when place inside the coil.

We bring the N-pole of the bar magnet near one end of the solenoid :- If there is an attraction, then that end of the solenoid has south polarity and the other has north polarity. If there is a repulsion, then that end of the solenoid has north polarity and the other end has south polarity.

Q.9. When is the force experienced by a current carrying conductor placed in a magnetic field largest?

Ans :- When the conductor carries current in a direction perpendicular to the direction of the magnetic field, the force experienced by the conductor is largest.

Q.10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam moving horizontally with back towards the front wall is defected by a strong magnetic field to your right side. what is the direction of the magnetic field?

Ans :- The magnetic field will be acting in vertically downward direction in accordance with Fleming’s left hand rule.

Q.11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in electric motor?

Ans :- Principle :- Electric motor is based upon Flemings left hand rule. When a current carrying conductor capable of free movement Is placed in a magnetic field, it experiences a mechanical force and begin to move in a direction given by Fleming’s left hand rule.

Construction :- A DC motor consists of single coil ABCD called armature between the pole pieces of a magnet as shown in fig. Armature consists of a coil of a large number of turns of insulated wire wrapped on a soft iron core. The two ends of the armature are connected to segments S₁ and S₂ of a commutator. The brushes B₁ and B₂ keep their contact with the commutator as it rotates.

Working :- A direct current from a battery is passed through armature. The current flows in the coil along ABCD as shown in fig (a). The limb AB of the coil experience downwards and CD of the coil experience upward force in accordance with Fleming’s left hand rule. These two equal and apposite forces constitute a couple tending to rotate the coil in clockwise direction. After half the rotation, brush B₁ has contact with S₂ and brush B₂ with S₁. The direction of the current gets reversed. The current now flows along DCBA instead of along ABCD. Limb DC experiences downward and BA experiences an upward force in accordance with Fleming’s left hand rule.

The process repeats itself and motion of armature becomes continuous after some time.

Split rings help in reversing the current in the coil after every half rotation.

Q.12. Name some devices in which electric motors are used.

Ans :- Electric fans, washing machines, mixers, computers etc.

Q.13. A coil of insulated copper wire is connected to galvanometer. What will happen if a bar magnet is

( a ) Pushed into the coil.

( b ) With drawn from inside the coil.

( c ) Held stationary inside the coil?

Ans :- ( i ) An electric current is induced in the coil and the galvanometer shows a deflection.

( ii ) When the bar is with drawn, there will again be momentarily a deflection but in a direction opposite to that when magnet was pushed.

( iii ) When the magnet is held stationary in the coi, there will be no deflection in galvanometer.

Q.14. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed will some current be induced coil B? Give reason.

Ans :- When the current in coil A is changed, some current is induced in the coil B. Due to the change in current in coil A, the magnetic field lines linked with coil A and with coil B get changed. This sets up induced current in coil B.

Q.15. State the rule to determine the direction of a

( i ) Magnetic field produced around a straight conductor carrying current.

( ii ) Force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it, and

( iii ) Current induced in a coil due to its rotation in a magnetic field.

Ans :- ( i ) Right hand thumb rule will determine the direction of a magnetic field around a straight conductor carrying current.

( ii ) Fleming’s left hand rule will determine the direction of a force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.

( iii ) Fleming’s right hand rule will determine the direction of current induced in a coil due to its rotation in a magnetic field.

Q.16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Ans :- In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.

An electric generator, as shown in fig consists of a rotating rectangular coil ABCD placed between the two poles of a permanent magnet. The two ends of this coil are connected to the two rings R₁ and R₂. The inner side of these rings are made insulated. The two conducting stationary brushes B₁ and B₂ are kept pressed separately on the rings R₁ and R₂ respectively. The two rings R₁ and R₂ are internally attached to an axle. The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. Outer ends of the two brushes are connected to the galvanometer to show the flow of current in the given external circuit.

When the axle attached to the two rings is rotated such that the arm AB moves up in the magnetic field produced by the permanent magnet.

Let us say the coil ABCD is rotated clockwise in the arrangement shown in fig. By applying Fleming’s right hand rule, the induced currents are set up in these arms along the directions AB and CD. Thus an induced current flows in the direction ABC.. If there are larger numbers of turns in the coil, the current generated in each tarns adds up to give a large current through the coil. This means that the current in the external circuit flows from B₂ to B₁.

After half a rotation, arm CD starts moving up an AB moving down. As a result, the direction of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA. The current in the external circuit now flows from B₁ to B₂ Thus after 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 direction after equal intervals of time is called an alternating current. This device is called an AC generator.

To get a direct current, 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. We have seen the working of a split ring commutator in the case of an electric motor. Thus a unidirectional current is produced. The generator is thus called a DC generator.

Q.17. When does an electric short circuit occur?

Ans :- Overloading can occur when then live wire and the neutral wire come into direct contact. This occurs when the insulation of wires is damaged or there is a fault in the appliance. In such situation the current in the circuit abruptly increases. This is called short- circuiting.

Q.18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Ans :- The earth wire connects the metallic body of the high powered appliance to the earth. It is a safety measure which ensures any leakage of current of the metallic body of the appliance keeps its potential equal to that of the earth and the user may not get a sever electric shock.

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