Goyal Brothers Prakashan solutions for अ न्यू अप्रोच टू आईसीएसई [अंग्रेजी] कक्षा १० chapter 9 - 1. Electromagnetism 2. Magnetic Effects of Electric Current 3. Electromagnetic Induction [Latest edition]

State the condition when an electric charge can give rise to a magnetic field.

Diagram alongside shows a freely pivoted magnetic needle. A copper conductor is held parallel to the magnetic axis of the needle. In which direction the north pole of needle moves in the following situations:

1. When the copper conductor is above the magnetic needle and current flows from A to B?
2. When the copper conductor is below the magnetic needle and current flows from A to B?
3. Why does the magnetic needle move in the situations (i) and (ii)?
4. Name and state the law, which helped you to find answer (i) and (ii).

Diagram alongside shows a smooth, but stiff cardboard ABCD, held horizontally, such that a straight thick copper conductor passes through the middle of cardboard. On the cardboard are sprinkled fine iron filings. A current is made to flow through the conductor as shown in diagram.

1. Copy the diagram and describe what happens to the iron filings? Give an explanation.
2. If instead of iron filings, a plotting magnetic compass is used, draw the magnetic line of force produced in diagram and show its direction.
3. Name and state two rules by which you can find the direction of magnetic field around the straight conductor carrying current.

1. Copy the adjacent diagram and plot magnetic fields around A and B for the circular coil, when the current flows through it.
2. State one way of increasing the magnetic intensity of the circular coil.
3. Give two characteristics of the magnetic field produced by the coil.
4. What is the direction of magnetic field with respect to the plane of circular coil?
5. What polarity (magnetic) is produced on the coil facing you?

What is an electromagnet?

State four ways of measuring the strength of an electromagnet.

State two common uses of electromagnets?

State two advantages of an electromagnet over a bar magnet.

How can you demagnetise a bar magnet by employing alternating current?

A current-carrying solenoid is suspended so as to freely rotate in a horizontal plane. State in what direction will it rest. Give a reason for your answer.

or

When a solenoid that is carrying current is freely suspended, it comes to rest in a particular direction. Why does this happen?

The diagrams (a), (b) and (c) show a smooth, but stiff cardboard, held horizontally, such that a thick copper wire passes through the middle of cardboard. The direction of the current is shown by arrows. Copy the diagrams.

1. In the diagrams (a) and (b) show the magnetic field due to conductor, showing at least four magnetic lines force. Assume there is no magnetic field due to earth.
2. In the diagram (c) show the magnetic field due to conductor when earth's magnetic field is acting by four magnetic lines of force.

The diagram given below shows a copper wire wound around a U-shaped soft iron bar. An iron pin is brought near the arrangement. First Source P and then Source Q are connected across AB, each operating independently.

(a) State true or false:

Source P as well as Source Q, when connected across AB, can attract the iron pin.

(b) Justify your answer to (a) with a suitable reason.

1. The figure alongside shows an electromagnet. What is the polarity at the end of X?
2. Suggest a way by which the strength of the electromagnet referred to can be measured.

1. The diagram alongside shows a freely suspended copper conductor carrying current held in between the pole pieces of a permanent magnet. State whether conductor will move into the plane of paper or out of the plane of paper.
2. Why does copper conductor move?
3. State the rule which determines motion of conductor.
4. State three factors which determine the force acting on conductor.

The diagram shows a rectangular coil ABCD, suspended freely between the concave pole pieces of a permanent horseshoe magnet, such that the plane of the coil is parallel to the magnetic field.

1. State your observation when the current is switched on.
2. Give an explanation for your observation in (i).
3. State the rule, which will help you to find the motion of rotation of the coil.
4. In which position will the coil ultimately come to rest?
5. State four ways of increasing the magnitude of force acting on the coil.

Draw a labelled diagram of a D.C. motor showing its main parts.

What is the function of radial magnets in a d.c. motor?

What is the function of insulated copper coil in d.c. motor?

What is the function of soft iron core in d.c. motor?

What is the function of the split rings in a d.c. motor?

What is the function of brushes in an electric generator?

State the position of armature coil relative to the direction of magnetic field, in a D. C. motor when the deflecting couple acting an the coil is maximum.

State the position of armature coil relative to the direction of magnetic field, in a D. C. motor when the deflecting couple acting and the coil is minimum.

How is the jerky motion of the coil converted into smooth circular motion?

State three ways of making a motor powerful.

A wire carrying a current is held over a freely suspended magnetic needle, such that the current in the wire flows from south to north. The direction in which the north end of freely suspended magnetic needle will point towards:

In an electric motor:

By reversing the direction of the current in an electromagnet, the magnetic field produced by it:

The power of a d.c. motor can be increased:

Commutator is a device in a d.c. motor which:

Which is not the use of an electromagnet?

The magnetic field of solenoid can not be increased by:

A thick copper conductor is held parallel to a freely pivoted magnetic needle, as shown in the diagram alongside. Answer the question given below:

The direction in which the north pole of the pivoted magnetic needle will point when current flows from north to south is:

A thick copper conductor is held parallel to a freely pivoted magnetic needle, as shown in the diagram alongside. Answer the question given below:

If the magnitude of current in the conductor is gradually increased the maximum angle through which magnetic needle will turn is :

A thick copper conductor is held parallel to a freely pivoted magnetic needle, as shown in the diagram alongside. Answer the question given below:

If the conductor is held below the magnetic needle and parallel to it, then the direction which north pole of pivoted magnetic will point, is:

A thick copper conductor is held parallel to a freely pivoted magnetic needle, as shown in the diagram alongside. Answer the question given below:

The direction of the magnetic field set up by the conductor carrying current is:

Which is not the characteristic of the magnetic field set up by a straight conductor carrying current?

A straight conductor carrying current passes through a rectangular cardboard as shown in the diagram. The magnetic lines of force around point A are in:

The law which helped you to find the direction of magnetic field lines is:

Which is the incorrect statement? When a current flows through a conductor,

A conductor carrying current cannot produce electrostatic force because:

Which is not the property of magnetic lines of force around a straight conductor carrying current?

Study the diagram alongside carefully and answer the following question:

The direction of the magnetic lines of force around A and B will be:

Study the diagram alongside carefully and answer the following question:

The magnetic lines of force within the coil are:

Study the diagram alongside carefully and answer the following question:

In the coil facing you, the direction of the current is clockwise. Therefore, the face of the coil towards you will have:

Which is not a property of the magnetic lines of force around a circular coil carrying current?

If a rod of soft iron is placed within hollow tube of solenoid and electric current is passed, the arrangement is called:

Which is not the correct statement regarding an electromagnet?

Study the diagram alongside carefully and answer the following question:

When the current is made to flow through a copper conductor, the direction of the magnetic field set up by the conductor is:

Study the diagram alongside carefully and answer the following question:

Due to two magnetic fields, i.e., the permanent magnet and the magnetic field set up by the conductor, the force experienced by the conductor depends upon:

Study the diagram alongside carefully and answer the following question:

The direction in which the conductor will move is:

Study the diagram alongside carefully and answer the following question:

The law which helped you to find the direction of motion of the conductor is:

Assertion (A): When a permanent bar magnet is placed in a solenoid connected to a.c. source, it gets demagnetised.

Reason (R): The alternating current rapidly changes the magnetic polarity which in turn disturbs magnetic molecular straight chains, to form closed chains and hence demagnetise the magnet.

Assertion (A): A conductor carrying a current can produce an electrostatic field.

Reason (R): The net positive or negative charge on the conductor is zero.

Assertion (A): A coil of many turns of an insulated copper wire is wound over soft iron core.

Reason (R): The strength of electromagnet increases with the increase in the magnitude of current.

Assertion (A): In the presence of magnetic field, the needle of a compass aligns itself in the direction of magnetic field.

Reason (R): The needle of a compass always points in the north-south direction in the absence of any other magnetic field.

Assertion (A): When a current flows through a metallic straight conductor, a magnetic field is set up at right angles to the direction of flow of current.

Reason (R): The flowing electrons act like tiny magnets.

Magnetic lines of forces around a conductor carrying electric current are in the form of ______ lines.

A coil facing you has current flowing in a clockwise direction. The face of coil will have ______ polarity.

A strong electromagnet has large number of turns wound over a ______ soft iron core.

In an electric motor the electric energy changes to ______.

By reversing the direction of current in an electromagnet the magnetic field produced by it ______.

Match the statements in Column A with those in Column B.

1. A transformer is designed to work on 200 V A.C mains, such that its output voltage is 6.0 V. Its primary coil has 6000 turns. Draw the fully labelled diagram of transformer.
2. State the principle involved in the construction of the above transformer.
3. Why is the secondary coil of this transformer far thicker than the primary coil?
4. Why is the core of this transformer laminated?
5. Can this transformer operate on 200 V D.C mains? Give a reason for your answer.
6. Can the efficiency of this transformer be 100%? Explain your answer.
7. How many turns are in the secondary coil?

Why do we need a step-up transformer for long-distance transmission of electric power?

Why is the e.m.f. at consuming centers dropped to 220 V by a step-down transformer?

State three characteristics of the primary coil of a step-up transformer.

State three characteristics of the secondary coil of a step-up transformer.

Figure alongside shows a coil connected to a centre zero galvanometer. The galvanometer shows deflection to the right, when the north pole of a powerful magnet is moved towards right.

1. Explain, why deflection occurs in the galvanometer?
2. What is the direction of current when viewed from end A?
3. What is your observation in G, when coil AB is moved from N?
4. What is your observation in G, when both coil AB and the magnet are moved towards right at the same speed?

The given diagram shows the output of an AC generator. If the speed of the generator coil is doubled, then:

1. what is the effect on the physical quantity indicated by ‘a’?
2. what is the effect on the physical quantity indicated as ‘b’?
3. give a reason for your answer in (b).

Which coil of a step up transformer is made thicker and why?

Name the transformer used in the power transmitting station of a power plant.

What is the nature of the current transmitted from the power station?

At what voltage is this current available to our household?

State two causes of energy loss in a transformer.

In the transmission of power the voltage of power generated at the generating stations is stepped up from 11kV to 132 kV before it is transmitted. Why?

How is the e.m.f. across primary and secondary coils of a transformer related with the number of turns of the coil in them?

On which type of current do transformers work?

Draw and label the diagram of an AC generator.

How is fluctuating current produced in an AC generator made smooth?

Answer the following question regarding an a.c. generator.

Why is the e.m.f. produced by the generator zero at a certain instant and maximum at some other instant when the coil is rotating at a constant speed?

Answer the following question regarding an a.c. generator.

When the current flowing in the external circuit is increased by decreasing the resistance, more power is required to drive the generator at the same speed. Explain.

What is an AC generator?

What is the function of the following in a dynamo?

Concave cylindrical magnets

What is the function of the following in a dynamo?

Laminated soft iron core

What is the function of the following in a dynamo?

Slip rings

What is the function of the following in a dynamo?

Brushes

On which phenomenon does the dynamo work? Define the phenomenon.

Explain the effect of current generated when magnetic field is increased.

Explain the effect of the current generated when the number of turns in the coil is increased.

In which position of the coil is the magnitude of the induced e.m.f. maximum?

In which position of the coil is the magnitude of the induced e.m.f. minimum?

The diagram below shows the core of a transformer and its input and output connections.

1. State the material used for the core.
2. Copy and complete the diagram of the transformer by drawing input and output coils.

State two dis-similarities between a d.c. motor and an a.c. generator.

A magnet kept at the centre of two coils A and B is moved to and fro as shown in the diagram. The two galvanometers show deflection. State with a reason whether : x > y or x< y    [x and y are magnitudes of deflection.]

The direction of current in a conductor can be obtained by:

A coil is held in a magnetic field, such that plane of the coil is at right angles to that of the plane of permanent magnet. The force experienced by the coil on the passage of electric current will be:

The phenomenon of electromagnetic induction was discovered by:

Figure alongside shows insulated copper coil connected to centre zero galvanometer. The galvanometer shows deflection to the right when the north pole of a powerful magnet is moved to the right. Answer the following question:

The galvanometer shows deflection because:

Figure alongside shows insulated copper coil connected to centre zero galvanometer. The galvanometer shows deflection to the right when the north pole of a powerful magnet is moved to the right. Answer the following question:

 When the movement of the magnet towards right stopped, then:

Figure alongside shows insulated copper coil connected to centre zero galvanometer. The galvanometer shows deflection to the right when the north pole of a powerful magnet is moved to the right. Answer the following question:

When the north pole of magnet is withdrawn towards left, the galvanometer shows:

Figure alongside shows insulated copper coil connected to centre zero galvanometer. The galvanometer shows deflection to the right when the north pole of a powerful magnet is moved to the right. Answer the following question:

When the north pole of permanent magnet moves towards right the deflection of current in the coil is in:

Figure alongside shows insulated copper coil connected to centre zero galvanometer. The galvanometer shows deflection to the right when the north pole of a powerful magnet is moved to the right. Answer the following question:

The magnetic polarity induced at the end is:

For an ideal step up transformer:

Assertion (A): The efficiency of a transformer is never 100%.

Reason (R): The energy is lost because of resistances of primary and secondary coils and eddy currents produced in core.

Assertion (A): The a.c. motor is based on the principle of electromagnetic induction.

Reason (R): The direction of induced current in coil is given by Faraday's right hand rule.

Assertion (A): More powerful is the inducing magnet, more is the magnitude of induced e.m.f. in a closed coil.

Reason (R): Magnetic energy of the powerful magnet changes into electric energy.

Assertion (A): A single coil of many turns produces fluctuating e.m.f. in a.c. generator.

Reason (R): The coil in the a.c. generator is moving at a slow speed.

Assertion (A): Primary coil of step up transformer is thinner as it has more turns than the secondary coil.

Reason (R): The induced e.m.f. produced in secondary coil is directly proportional to number of turns in the secondary coil.

When the magnetic flux changes in a closed coil an ______ current is produced in the coil.

When the magnetic flux changes in a closed coil in an open circuit ______ induced current is produced.

About 10% of the energy is wasted in step up transformer, because of ______ produces in its core.

The generating e.m.f at the power stations is ______ for transmission to consuming centres.

An a.c dynamo converts ______ energy into electric energy.

Match the statements in Column A with those in Column B.

The given rods will attract each other when:

A magnetic compass is present on a small table, very close to the wall in a room. A man enters the room and switches on the Air Conditioner fitted near the ceiling. He observes that the needle in the compass shows immediate deflection. Identify the most probable reason for the deflection.

Assertion (A): When current is passed through a wire, a magnetic field is generated around the wire.

Reason (R): Whenever there is a change of magnetic flux linked up with the coil, the induced current is generated in the coil.

A straight wire is passed vertically through cardboard sprinkled with iron filings.

1. When current is passed through the wire in the upward direction, it is seen that the iron fillings are arranging themselves in a definite pattern. Why?
2. What would happen to this arrangement if more current were passed through the wire?

The diagram shows a copper conductor placed along the east-west direction. Magnetic compass P is present above the conductor, and Q is below the conductor. If current is passed through the wire from A to B, then which of the two compasses will show prominent deflection and why?

Read the excerpt from a story and answer the questions that follow:

1. Explain the secret behind the magic.
2. If you are asked to design the same magic in your science lab, give the necessary circuit diagram.
3. Give any one device that works on the same principle.

In the given diagram, X represents a conductor carrying current into the plane of the paper and kept in a magnetic field. N and S represent the poles of a magnet and the concentric circles of the magnetic field produced by the conductor.

1. State the direction of the force experienced by the conductor.
2. Explain the cause of the above-said force.
3. Name the law used to determine the direction of the force in the conductor.

The circuit diagram illustrates a copper bar placed on two copper wires stretched over a wooden base placed between two poles of magnets. This entire setup is placed on a compression balance, which shows a weight of 0.4 kgf.

1. What will be the observation of the compression balance when we close the switch?
2. How will this observation change when we increase the current in the circuit?
3. Name the rule used to come to the conclusion in (a).

The diagram shows two parallel wires carrying current in the downward direction. The magnitude of the current in wire A is greater than in wire B. It is also observed that the wires exert force on each other.

1. State the direction of the force experienced by wire A.
2. Name the law/laws used to come to the conclusion in (a).
3. When a compass is placed between the two wires, it does not remain along the direction of the magnetic field of wire A or wire B at one of the points P, Q, or R. State, with a reason, at which point you will observe this.