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# Selina solutions for Class 10 Physics chapter 10 - Electro-Magnetism

## Chapter 10: Electro-Magnetism

#### Chapter 10: Electro-Magnetism solutions [Page 0]

Describe an experiment to demonstrate that there is a magnetic field around a current carrying conductor.

Draw a diagram showing the directions of three magnetic field lines due to a straight wire carrying current. Also show the direction of current in the wire.

How is the magnetic field due to a straight current carrying wire affected if current in wire is decreased ?

How is the magnetic field due to a straight current carrying wire affected if current in wire is reversed?

State a law, which determines the direction of magnetic field around a current carrying wire.

A straight wire lying in a horizontal plane carries a current from north to south. (a) What will be the direction of magnetic field at a point just underneath it? (b) Name the law used to arrive at the answer in part (a).

What will happen to a compass needle when the compass is placed below a wire and a current is made to flow through the wire? Give a reason to justify your answer.

Draw a labelled diagram showing the three magnetic field lines of a loop carrying current. Mark the direction of current and the direction of magnetic field by arrows in your diagram.

A wire, bent into a circle, carries current in an anticlockwise direction. What polarity does this face of the coil exhibit?

What is the direction of magnetic field at the centre of a coil carrying current in  clockwise ?

What is the direction of magnetic field at the centre of a coil carrying current in anticlockwise direction?

Draw a diagram to represent the magnetic field lines along the axis of a current carrying solenoid mark arrows to show the direction of current in the solenoid and the direction of magnetic field lines.

Name and state the rule by which polarity at the ends of a current carrying solenoid is determined.

The adjacent diagram shows a small magnet placed near a solenoid AB. Current is switched on in the solenoid by pressing the key K. (a) State the polarity at the ends A and B. (b) will the magnet be attracted or repelled? Give a reason for your answer.

The following diagram shows a spiral coil wound on a hollow carboard tube AB. A magnetic compass is placed close to it. Current it switched on by closing the key. (a) What will be the polarity at the ends A and B? (b) How will the compass needle be affected? Give reason.

State two ways by which the magnetic field due to a solenoid can be made stronger.

Why does a current carrying freely suspended solenoid rest along a particular direction?

What effect will there be on magnetic compass when it is brought near a current carrying solenoid?

How is the magnetic field due to a solenoid carrying current affected if a soft iron bar is introduced inside the solenoid?

Complete the following sentence :
when current flows in a wire, it creates ………..

Complete the following sentence :

A current carrying solenoid behaves like a ……………

Complete the following sentence :

A current carrying solenoid when freely suspended, it always rests in ………. Direction .

You are required to make an electromagnet from a soft iron bar by using a cell, an insulated coil of copper wire and a switch. (a) Draw a circuit diagram to represent the process. (b) label the poles of the electromagnet.

The adjacent diagram shows a coil would around a soft iron bar XY. (a) State the polarity at the end X and Y as the switch is pressed. (b) Suggest one way increasing the strength of electromagnet so formed.

(a) What name is given to a cylindrical coil of diameter less than its length? (b) If a piece of soft iron is placed inside the coil mentioned in part (a) and current is passed in the coil from a battery, what name is then given to the device so obtained? (c) Give one use of the device mentioned in part (b).

Show with the aid of a diagram how a wire is wound on a U-shaped piece of soft iron in order to make it an electromagnet. Complete the circuit diagram and label the poles of the electromagnet.

What is an electromagnet?

Name two factors on which the strength of magnetic field of an electromagnet depends and state how does it depend on the factors stated by you.

Fig. 10.20 shows the current flowing in the coil of wire wound around the soft iron horse shoe core. State the polarities developed at the ends A and B.

State two ways through which the strength of an electromagnet can be increased.

State three uses of an electromagnet?

State two advantages of an electromagnet over a permanent magnet.

State two differences between an electromagnet and a permanent magnet.

Why is soft iron used as the core of the electromagnet in an electric bell?

How is the working of an electric bell affected, if alternating current be used instead of direct current?

The incomplete diagram of an electric bell is given in Fig 10.21 Complete the diagram and label its different parts.

Name the material used for making the armature of an electric bell. Give a reason for your answer.

#### Chapter 10: Electro-Magnetism solutions [Page 0]

The present of magnetic field at a point can be detected by:
(a) a strong magnet
(b) a solenoid
(c) a compass needle
(d) a current carrying wire

By reversing the direction of current in a wire, the magnetic field produced by it:
(a) gets reversed in direction
(b) increases in strength
(c) decreases in strength
(d) remains unchanged in strength and direction

#### Chapter 10: Electro-Magnetism solutions [Page 0]

Name three factors on which the magnitude of force on a current carrying conductor placed in a magnetic field depends and state how does the force depend on the factors stated by you.

State condition when magnitude of force on a current carrying conductor placed in a magnetic field is Zero ?

State condition when magnitude of force on a current carrying conductor placed in a magnetic field is maximum ?

Name and state the law which is used to determine the direction of force on a current carrying conductor placed in a magnetic field.

How will the direction of force be changed, if the current is reversed in the conductor placed in a magnetic field?

State the unit of magnetic field in terms of the force experienced by a current carrying conductor placed in a magnetic field

A flat coil ABCD is freely suspended between the pole pieces of U-Shaped permanent magnet with the plane of coil parallel to the magnetic field.
(a) What happens when a current is passed in the coil?
(b) when will the coil come to rest?
(c) when will the couple acting on the coil be (i) maximum (ii) minimum?
(d) Name an instrument which makes use of the principle stated above.

A coil ABCD mounted on an axle is placed between the poles N and S of a permanent magnet as shown in Fig. 10.28

(a) In which direction will the coil begin to rotate when current is passed through the coil in direction ABCD by connecting a battery at the ends A and D of the coil?
(b) Why is a commutator necessary for continuous rotation of the coil?
(c) Complete the diagram with commutator, ets. For the flow of current in the coil?

What is an electric motor?

principle of an electric motor ?

Draw a labelled diagram of a d.c. motor.

What energy conversion does take place during the working of a d.c. motor?

State two ways by which the speed of rotation of an electric motor can be increased?

Name two appliances in which an electric motor is used.

Complete the following sentence :
……… energy is converted into …………energy by an electric motor.

#### Chapter 10: Electro-Magnetism solutions [Page 0]

In an electric motor the energy transformation is:
(a) from electrical to chemical
(b) from chemical to light
(c) from mechanical to electrical
(d) from electrical to mechanical

#### Chapter 10: Electro-Magnetism solutions [Page 0]

What is electromagnetic induction?

Describe one experiment to demonstrate the phenomenon of electromagnetic induction.

In the figure:

State Faraday’s law of electromagnetic induction.

State two factors on which the magnitude of induced e.m.f. depend.

What kind of energy change takes place when a magnet is moved towards a coil having a galvanometer at its ends?

Name the phenomenon ?

(a) How would you demonstrate that a momentary current can be obtained by the suitable use of a magnet, a coil of wire and a galvanometer?
(b) What is the source of energy associated with the current obtained in part(a)?

Describe briefly one way producing an induced e.m.f ?

State one factor that determines the magnitude of induced e.m.f ?

What factor determines the direction of induced e.m.f?

Complete the following sentence:
The current induced in a closed circuit only if there is ……………..

In which of the following case does the electromagnetic induction occur?

A current is started in a wire held near a loop of wire ?

In which of the following case does the electromagnetic induction occur?
The current is stopped in a wire held near a loop of wire .

In which of the following case does the electromagnetic induction occur?

A magnet is moved through a loop of wire .

In which of the following case does the electromagnetic induction occur?

A loop of wire is held near a magnet.

A conductor is moved in a varying magnetic field. Name the law which determines the direction of current induced in the conductor.

State Fleming’s right hand rule.

What is Lenz’s law?

Why is it more difficult to move a magnet towards a coil which has large number of turns?

Explain why an induced current must flow in such a direction so as to oppose the change producing it.

Explain the significance of Lenz’s law to show the conservation of energy in electromagnetic induction.

The following diagram in Fig.10.42 shows a coil of several turns of copper wire connected to a sensitive centre zero galvanometer G near a magnet NS. The coil is free to move in the direction shown in the diagram.

(i) Describe the observation if the coil is rapidly moved.
(ii) How would the observation be altered if (a) the coil has twice as many turns (b the coil was made to move three times as fast?

The following diagram in Fig. 10.43 shows a fixed coil of several turns connected to a centre zero galvanometer G and a magnet NS which can move in the direction shown in the diagram.
(a) Describe the observation in the galvanometer if (i) the magnet is moved rapidly,(ii) the magent is kept still after it has moved into the coil, (iii) the magent is then rapidly pulled out of the coil.

(b) How would the observation in (i) of part (a) alter if a more powerful magnet is used?

The following diagram in Fig. 10.44 shows a coil X connected to a sensitive centre –zero galvanometer G and a coil P connected to a battery through a switch S.

(a) Describe the observation when the switch S is (i) closed suddenly, (ii) then kept closed, (iii) finally opened.
(b) Name and state the law which explains the above observations.

Name and state the principle of a simple a.c. generator what is its use?

What determines the frequency of a.c. produced in a generator?

Draw a labelled diagram of a simple a.c. generator.

In an a.c. generator the speed at which the coil rotates is doubled. How would this affect (a) the frequency of output voltage, (b) the maximum output voltage is doubled.

Suggest two ways in an a.c. generator to produce a higher e.m.f.

What energy conversion does take place in a generator when it is in use?

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

State one advantage of using a.c. over d.c.

For what purpose are the transformers used? Can they be used with a direct current source?

How are the e.m.f in the primary and secondary coils of a transformer related with the number
of turns in these coils?

Draw a labelled diagram to show the various components of a step-up transformer.

Name the device used to transform 12 V a.c. to 200V a.c. Name the principal on which it
works.

Draw a labelled diagram of a step-up transformer and explain how it works. State two
characteristics of the primary coil as compared to its secondary coil.

Draw a labelled diagram of a device you would use to transform 200 V a.c. to 15 V a.c. Name the device and explain how it works. Give its tow uses.

Complete the following diagram in Fig. 10.45 of a transformer and name the parts labelled A and B. name the part you have drawn to complete the diagram. What is the material of this part? Is this transformer a step up or step down? Give reason.

The diagram below in Fig. 10.46 shows the core of a transformer and its input and output connections.

(a) state the material used for core and describe its structure.

(b) complete the diagram of the transformer and connections by labelling all parts joined by you.
(c) Name the transformer: Step-up or step down?

The secondary windings of a transformer in which the voltage is stepped down are usually made of thicker wire than the primary. Explain why.

Why is the iron core of a transformer made laminated (thin sheets) instead of being in one solid piece?

Complete the following sentence:
In a step-up transformer, the number of turns in the primary are …………than the number of turns in the secondary.

Complete the following sentence :

The transformer is used in ……………. current circuits.

Complete the following sentence :

………………….. energy is converting into …………. energy by an electric generator.

What is the function of a transformer in an a.c. circuit? How do the input and output powers in a transformer compare?

Name one kind of energy loss in a transformer. How is it minimized?

Give two points of difference between a step-up transformer and step-down transformer.

Name the material of core in (a) electric bell, (b) electromagnet (c) d.c motor, (d) an a.c. generator and (e) transformer.

#### Chapter 10: Electro-Magnetism solutions [Page 0]

The direction of induced current is obtained by:
(a) Feming’s left hand rule
(b) Clock rule
(c) Right hand thumb rule
(d) Fleming’s right hand rule

In a step up transformer:
(a) NS = NP (b) NS < NP
(c) NS > NP (d) nothing can be said

#### Chapter 10: Electro-Magnetism solutions [Page 0]

The primary coil of a transformed has 800 urns and the secondary coil has 8 turns. It is connected to a 220 V a.c. supply. What will be the output voltage?

A transformer is designed to work from a 240 V a.c. mains and to give a supply of 8 V to ring
a house–bell. The primary coil has 4800 turns. How many turns will be in the secondary coil?

The input and output voltage of a transformer are 220 V and 44 V respectively. Find: (a) the
turns ratio, (b) the current in input circuit if the output current is 2 A.

## Selina solutions for Class 10 Physics chapter 10 - Electro-Magnetism

Selina solutions for Class 10 Physics chapter 10 (Electro-Magnetism) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CISCE Selina ICSE Concise Physics for Class 10 solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Class 10 Physics chapter 10 Electro-Magnetism are Flemingâ€™S Right Hand Rule, Ac Generator, Flemingâ€™s Left Hand Rule, Magnetic Effect of a Current, Electromagnetic Induction, Concept of Transformer, Concept of Electro Magnetism.

Using Selina Class 10 solutions Electro-Magnetism exercise by students are an easy way to prepare for the exams, as they involve solutions arranged chapter-wise also page wise. The questions involved in Selina Solutions are important questions that can be asked in the final exam. Maximum students of CISCE Class 10 prefer Selina Textbook Solutions to score more in exam.

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