Solution of Chapter 2. Magnetic Effects of Electric Current (Lakhmir Singh & Manjit Kaur - Physics Book)

State any two properties of magnetic field lines.

What are the two ways in which you can trace the magnetic field pattern of a bar magnet?

You are given the magnetic field pattern of a magnet. How will you find out from it where the magnetic field is the strongest ?

State whether the following statement is true or false :

The axis of earth's imaginary magnet and the geographical axis coincide with each other.

Why does a compass needle get deflected when brought near a bar magnet?

Where do the manufacturers use a magnetic strip in the refrigerator? Why is this magnetic strip used?

Fill in the following blanks with suitable words :

(a) Magnetic field lines leave the..........pole of a bar magnet and enter at its........pole.

(b) The earth's magnetic field is rather like that of a ......... magnet with its........pole in the northern hemisphere.

Draw a diagram to show the magnetic field lines around a bar magnet

What is a magnetic field? How can the direction of magnetic field lines at a place be determined?

Explain why, two magnetic field lines do not intersect each other.

When an electric current is passed through any wire, a magnetic field is produced around it. Then why an electric iron connecting cable does not attract nearby iron objects when electric current is switched on through it?

Define magnetic field lines. Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another pole.

Explain why, a freely suspended magnet always points in the north-south direction.

A strong bar magnet is placed vertically above a horizontal wooden board. The magnetic lines of force will be:

The magnetic field lines produced by a bar magnet :

Which of the following is not attracted by a magnet ?

The magnetic field lines :

The north pole of earth's magnet is in the:

The axis of earth's magnetic field is inclined with the geographical axis at an angle of about:

The shape of the earth's magnetic field resembles that of an imaginary:

A magnet attracts:

A plotting compass is placed near the south pole of a bar magnet. The pointer of plotting compass will :

The metallic pointer of a plotting compass gets deflected only when it is placed near a bar magnet because the pointer has :

Which of the following statements is incorrect regarding magnetic field lines ?

Copy the figure given below which shows a plotting compass and a magnet. Label the N pole of the magnet and draw the field line on which the compass lies.

The diagram shows a bar magnet surrounded by four plotting compasses. Copy the diagram and mark in it direction of the compass needle for each of the cases B, C and D.

Which is the north pole, X or Y ?

The three diagrams in the following figure shows the lines of force (field lines) between the poles of two magnets. Identify the poles A, B, C, D, E and F.

The figure given below shows the magnetic field between two magnets:

(i) Copy the diagram and label the other poles of the magnets.

(ii) Which is the weaker magnet?

Which effect of current can be utilised in detecting a current-carrying wire cancelled in a wall?

What conclusion do you get from the observation that a current-carrying wire deflects a compass needle placed near it?

Name the scientist who discovered the magnetic effect of current.

State qualitatively the effect of inserting an iron core into a current-carrying solenoid.

Name the rule for finding the direction of magnetic field produced by a straight current-carrying conductor.

State the form of magnetic field lines around a straight current--++carrying conductor.

What is the other name of Maxwell’s right-hand thumb rule?

State whether the following statement is true or false:

The magnetic field inside a long circular coil carrying current will be parallel straight lines.

What is the shape of current-carrying conductor whose magnetic field pattern resembles that of a bar magnet?

State three ways in which the strength of an electromagnet can be increased.

Fill in the following blanks with suitable words:

(a) The lines of _____ round a straight-carrying conductor are in the shape of _____

(b) For a current-carrying solenoid, the magnetic field is like that of a _____

(d) The magnetic effect of a coil can be increased by increasing the number of _____, increasing the _____ or inserting an _____ core.

(e) If a coil is viewed from one end and the current flows in an anticlockwise direction, then this end is a _____ pole.

(f) If a coil is viewed from one end, and the current flows in a clockwise direction, then this end is a _____ pole.

Describe how you will locate a current-carrying wire concealed in a wall.

Describe some experiment to show that the magnetic field is associated with an electric current.

Draw a sketch to show the magnetic lines of force due to a current-carrying straight conductor.

Name and state the rule to determine the direction of magnetic field around a straight current-carrying conductor.

State and explain Maxwell's right-hand thumb rule.

What is Maxwell's corkscrew rule? For what purpose is it used?

Draw the magnetic lines of force due to a circular wire carrying current.

What are the various ways in which the strength of magnetic field produced by a current-carrying circular coil can be increased?

State and explain the Clock face rule for determining the polarities of a circular wire carrying current.

Name any two factors on which the strength of magnetic field produced by a current-carrying solenoid depends. How does it depend on these factors?

Draw a circuit diagram to show how a soft iron piece can be transformed into an electromagnet.

Describe how an electromagnet could be used to separate copper from iron in a scrap yard.

How does an electromagnet differ from a permanent magnet?

Name two devices in which electromagnets are used and two devices where permanent magnets are used.

What is a solenoid? Draw a sketch to show the magnetic field pattern produced by a current-carrying solenoid.

Name the type of magnet with which the magnetic field pattern of a current-carrying solenoid resembles.

What is the shape of field lines inside a current-carrying solenoid? What does the pattern of field lines inside a current-carrying solenoid indicate?

List three ways in which the magnetic field strength of a current-carrying solenoid can be increased?

What type of core should be put inside a current-carrying solenoid to make an electromagnet ?

What is an electromagnet? Describe the construction and working of an electromagnet with the help of a labelled diagram.

Explain why, an electromagnet is called a temporary magnet.

Explain why, the core of an electromagnet should be of soft iron and not of steel.

State the factors on which the strength of an electromagnet depends. How does it depend on these factors ?

Write some of the important uses of electromagnets

The strength of the magnetic field between the poles of an electromagnet would be unchanged if :

The diagram given below represents magnetic field caused by a current-carrying conductor which is:

The magnetic inside a long straight solenoid carrying current :

Which of the following correctly describes the magnetic field near a long straight wire?

The north-south polarities of an electromagnet can be found easily by using:

The direction of current in the coil at one end of an electromagnet is clockwise. This end of the electromagnet will be:

If the direction of electric current in a solenoid when viewed from a particular end is anticlockwise, then this end of solenoid will be:

The most suitable material for making the core of an electromagnet is:

The magnetic effect of current was discovered by:

A soft iron bar is inserted inside a current-carrying solenoid. The magnetic field inside the solenoid:

The magnetic field lines in the middle of the current-carrying solenoid are :

The front face of a circular wire carrying current behaves like a north pole. The direction of current in this face of the circular wire is:

The back face of a circular loop of wire found to be south magnetic pole. The direction of current in this face of the circular loop of wire will be:

In the straight wire A, current is flowing in the vertically downward direction whereas in wire B the current is flowing in the vertically upward direction. What is the direction of magnetic field:

(a) in wire A?

(b) in wire B?

Name the rule which you have used to get the answer.

The figure shows a solenoid wound on a core of soft iron. Will the end A be a N pole or S pole when the current flows in the direction shown?

A current-carrying straight wire is held in exactly vertical position. H the current passes through this wire in the vertically upward direction, what is the direction of magnetic field produced by it? Name the rule used to find out the direction of magnetic field.

For the coil in the diagram below, when the switch is pressed:

(a) What is the polarity of end A?

(b) Which way will the compass point then?

A current flows downwards in a wire that passes vertically through a table top. Will the magnetic field lines around it go clockwise or anticlockwise when viewed from above the table?

The directions of current flowing in the coil of an electromagnet at its two ends X and Y are as shown below:

(a) What is the polarity of end X?

(b) What is the polarity of end Y?

(c) Name and state the rule which you have used to determine the polarities.

The magnetic field associated with a current-carrying straight conductor is in anticlockwise direction. H the conductor was held along the east-west direction, what will be the direction of current through it? Name and state the rule applied to determine the direction of current?

A current-carrying conductor is held in exactly vertical direction. In order to produce a clockwise magnetic field around the conductor, the current should be passed in the conductor:

(a) from top towards bottom

(b) from left towards right

(c) from bottom towards top

(d) from right towards left

A thick wire is hanging from a wooden table. An anticlockwise magnetic field is to be produced around the wire by passing current through this wire by using a battery. Which terminal of the battery should be connected to the:

(a) top end of wire?

(b) bottom end of wire?

What happens when a current-carrying conductor is placed in a magnetic field?

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

In a statement of Fleming's left-hand rule, what do the following represent?

(a) direction of centre finger.

(b) direction of forefinger.

(c) direction of thumb.

Name one device which works on the magnetic effect of current.

Name the device which converts electrical energy into mechanical energy.

A motor converts one form of energy into another. Name the two forms.

State whether the following statement is true or false:

An electric motor converts mechanical energy into electrical energy.

For Fleming's left-hand rule, write down the three things that are 90° to each other, and next to each one write down the finger or thumb that represents it.

Name the device which is used to reverse the direction of current in the coil of a motor.

What is the other name of the split ring used in an electric motor?

What is the function of a commutator in an electric motor?

Of what substance are the brushes of an electric motor made ?

Of what substance is the core of the coil of an electric motor made?

In an electric motor, which of the following remains fixed and which rotates with the coil?

Commutator; Brush

What is the role of the split ring in an electric motor?

Fill in the following blanks with suitable words:

(a) Fleming's Rule for the motor effect uses the ............... hand.

(b) A motor contains a kind of switch called a ............ which reverses the current every half ............ .

A current-carrying conductor is placed perpendicularly in a magnetic field. Name the rule which can be used to find the direction of force acting on the conductor.

State two ways to increase the force on a current-carrying conductor in a magnetic field.

Name one device whose working depends on the force exerted on a current-carrying coil placed in a magnetic field.

State Fleming's left-hand rule. Explain it with the help of labelled diagrams.

What is the principle of an electric motor? Name some of the devices in which electric motors are used.

In a d.c. motor, why must the current to the coil be reversed twice during each rotation ?

What device reverses the current?

State what would happen to the direction of rotation of a motor if :

(i) the current were reversed

(ii) the magnetic field were reversed

(iii) both current and magnetic field were reversed simultaneously.

In what ways can a motor be made more powerful?

What is an electric motor? With the help of a labelled diagram, describe the working of a simple electric motor.

What are the special features of commercial electric motors?

In an electric motor, the direction of current in the coil changes once in each:

An electron beam enters a magnetic field at right angles to it as shown in the Figure.

The direction of force acting on the electron beam will be:

The force experienced by a current-carrying conductor placed in a magnetic field is the largest when the angle between the conductor and the magnetic field is:

The force exerted on a current-carrying wire placed in a magnetic field is zero when the angle between the wire and the direction of magnetic field is:

A current flows in a wire running between the S and N poles of a magnet lying horizontally as shown in Figure below:

The force on the wire due to the magnet is directed:

An electric motor is a device which transforms:

A magnetic field exerts no force on:

A horizontal wire carries a current as shown in Figure below between magnetic poles N and S:

Is the direction of the force on the wire due to the magnet:

In the simple electric motor of figure given below, the coil rotates anticlockwise as seen by the eye from the position X when current flows in the coil.

Is the current flowing clockwise or anticlockwise around the coil when viewed from above?

Which way does the wire in the diagram below tend to move?

H the current in a wire is flowing in the vertically downward direction and a magnetic field is applied from west to east, what is the direction of force on the wire?

Which way does the wire in the diagram below tend to move?

What is the force on a current-carrying wire that is parallel to a magnetic field? Give reason for your answer.

A charged particle enters at right angles into a uniform magnetic field as shown:

What should be the nature of charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field?

Name the device which converts mechanical energy into electric energy.

Out of an A.C. generator and a D.C. generator:

(a) which one uses a commutator (split rings)?

(b) which one uses slip rings?

Name the phenomenon which is made use of in an electric generator.

Name the rule which gives the direction of induced current.

What condition is necessary for the production of current by electromagnetic induction?

What type of generator is used at Power Stations?

What change should be made in an a.c. generator so that it may become a d.c. generator?

State whether the following statements are true or false:

(a) A generator works on the principle of electromagnetic induction.

(b) A motor works on the principle of electromagnetic induction.

What is the function of brushes in an electric generator?

When a wire is moved up and down in a magnetic field, a current is induced in the wire. What is this phenomenon known as?

When current is 'switched on' and 'switched off' in a coil, a current is induced in another coil kept near it.

What is this phenomenon known as?

What is the major difference between the simple alternator and most practical alternators?

Why are Thermal Power Stations usually located near a river?

List three sources of magnetic fields.

Complete the following sentence :

A generator with commutator produces..........current.

Two circular coils A and B are placed close to each other. If the current in coil A is changed, will some current be induced in the coil B? Give reason for your answer.

Explain the principle of an electric generator.

State two ways in which the current induced in the coil of a generator could be increased.

What is the difference between alternating current and direct current?

What type of current is given by

(i) a dry cell, and

(ii) a Power House generator?

State and explain Fleming's right hand rule.

Name and state the rule to find the direction of:

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

(b) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it.

In what respect does the construction of an A.C. generator differ from that of a D.C. generator?

What normally drives the alternators in a Thermal Power Station? What fuels can be used to heat water in the boiler?

Draw the labelled diagram of an A.C. generator. With the help of this diagram, explain the construction and working of an A.C. generator.

What do you understand by the term "electromagnetic induction"? Explain with the help of a diagram.

Name one device which works on the phenomenon of electromagnetic induction.

Describe different ways to induce current in a coil of wire.

What do you understand by the terms 'direct current' and 'alternating current'?

Name some sources of direct current and some of alternating current.

State an important advantage of alternating current over direct current.

What is the frequency of A.C. supply in India?

A rectangular coil of copper wire is rotated in a magnetic field. The direction of induced current changes once in each:

The phenomenon of electromagnetic induction is:

The device used for producing electric current is called a:

The essential difference between an AC generator and a DC generator is that:

When the switch Sis closed in the figure given below, the pointer of the galvanometer moves to the right.

If S is kept closed, will the pointer:

Each one of the following changes will increase e.m.f. (or voltage) in a simple generator except:

The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a galvanometer. The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly. The maximum deflection of the galvanometer was observed when the magnet was:

An electric generator converts:

A d.c. generator is based on the principle of:

An induced current is produced when a magnet is moved into a coil. The magnitude of induced current does not depend on :

The frequency of direct current (d.c.) is:

The frequency of alternating current (a.c.) supply in India is:

A coil is connected to a galvanometer. When the N-pole of a magnet is pushed into the coil, the galvanometer deflected to the right. What deflection, if any, is observed when:

(a) the N-pole is removed?

(b) the 5-pole is inserted?

(c) the magnet is at rest in the coil?

State three ways of increasing the deflection on the galvanometer.

When the magnet shown in the diagram below is moving towards the coil, the galvanometer gives a reading to the right.

(i) What is the name of the effect being produced by the moving magnet?

(ii) State what happens to the reading shown on the galvanometer when the magnet is moving away from the coil.

(iii) The original experiment is repeated. This time the magnet is moved towards the coil at a great speed.

If you hold a coil of wire next to a magnet, no current will flow in the coil. What else is needed to induce a current?

The wire in Figure below is being moved downwards through the magnetic field so as to produce induced current.

What would be the effect of:

(a) moving the wire at a higher speed?

(b) moving the wire upwards rather than downwards?

(c) using a stronger magnet?

(d) holding the wire still in the magnetic field?

(e) moving the wire parallel to the magnetic field lines?

Two coils A and B of insulated wire are kept close to each other. Coil A is connected to a galvanometer while coil B is connected to a battery through a key. What would happen if:

(i) a current is passed through coil B by plugging the key?

(ii) the current is stopped by removing the plug from the key?

A portable radio has a built-in transformer so that it can work from the mains instead of batteries. Is this a step-up or step down transformer?

What name is given to the device which automatically cuts off the electricity supply during short-circuiting in household wiring?

What is the usual capacity of an electric fuse used (i) in the lighting circuit, and (ii) in the power circuit, of a small house?

Give the symbol of an electric fuse used in circuit diagrams.

State whether the following statements are true or false:

(a) A wire with a green insulation is usually the live wire.

(b) A miniature circuit breaker (MCB) works on the heating effect of current.

Along with live wire and neutral wire, a third wire is also used in domestic electric wiring. What name is given to this third wire?

List the colours of the three wires in the cable connected to the plug of an electric iron.

What is the electric potential of the neutral wire in a mains supply cable ?

If fuses of 250 m A, 500 mA, 1 A, 5 A and 10 A were available, which one would be the most suitable for protecting an amplifier rated at 240 V, 180 W?

When does an electric short circuit occur?

In which wire in an A.C. housing circuit is the switch introduced to operate the lights?

In household circuits, is a fuse wire connected in series or in parallel?

Usually three insulated wires of different colours are used in an electrical appliance. Name the three colours.

What is the usual colour of the insulation of:

(a) live wire,

(b) neutral wire, and

(c) earth wire?

What is the main purpose of earthing an electrical appliance?

Give two reasons why different electrical appliances in a domestic circuit are connected in parallel.

How should the electric lamps in a building be connected so that the switching on or off in a room has no effect on other lamps in the same building?

Fill in the following blanks with suitable words:

(a) A fuse should always be placed in the .............wire of a mains circuit.

(b) The earth wire should be connected to the..............of an appliance.

Of what substance is the fuse wire made? Why?

Explain why, a copper wire cannot be used as a fuse wire.

What type of electric fuse is used in electrical appliances like car stereos? Explain with the help of a labelled diagram.

Distinguish between the terms 'overloading' and 'short-circuiting ' as used in domestic circuits.

When does a fuse cut off current? How does it do it?

What is the maximum number of 60 W bulbs that can be run from the mains supply of 220 volts if you do not want to overload a 5 A fuse?

Explain the importance of using in a household electric circuit

(i) fuse, and

(ii) earthing wire.

An electric iron is rated at 230 V, 750 W. Calculate

(i) the maximum current, and

(ii) the number of units of electricity it would use in 30 minutes.

Which of the following fuse ratings would be suitable for this electric iron ?

1 A, 3 A, 5 A, 13 A

What is the function of an earth wire? Why is it necessary to earth the metallic bodies of electrical appliances?

What current is taken by a 3 kW electric geyser working on 240 V mains?

What size fuse should be used in the geyser circuit?

Why are fuses fitted in the fuse box of a domestic electricity supply?

What device could be used in place of the fuses?

Draw a labelled diagram to show the domestic electric wiring from an electric pole to a room. Give the wiring for a bulb and a three-pin socket only.

State two hazards associated with the use of electricity.

State the important precautions which should be observed in the use of electricity.

What will you do if you see a person coming in contact with a live wire?

Explain why, electric switches should not be operated with wet hands.

At the time of short circuit, the current in the circuit:

A 1.25 kW heater works on a 220 V mains supply. What current rating would a suitable fuse have ?

The maximum number of 40 W tube-lights connected in parallel which can safely be run from a 240 V supply with a 5 A fuse is :

In normal use, a current of 3.5 A flows through a hair dryer. Choose a suitable fuse from the following:

Which one of the following statements is not true?

A car headlamp of 48 W works on the car battery of 12 V. The correct fuse for the circuit of this car headlamp will be:

A 3-pin mains plug is fitted to the cable for a 1 kW electric kettle to be used on a 250 V a.c. supply. Which of the following statement is not correct?

A TV set consumes an electric power of 230 watts and runs on 230 volts mains supply. The correct fuse for this TV set is :

Circuit Breaker Device which can be used in place of fuse in domestic electric wiring is called:

An MCB which cuts off the electricity supply in case of short-circuiting or overloading works on the:

An air-conditioner of 3.2 kW power rating is connected to a domestic electric circuit having a current rating of 10 A. The voltage of power supply is 220 V. What will happen when this air-conditioner is switched on? Explain your answer.

Three appliances are connected in parallel to the same source which provides a voltage of 220 V. A fuse connected to the source will blow if the current from the source exceeds 10 A. If the three appliances are rated at 60 W, 500 W and 1200 W at 220 V, will the fuse blow?

A vacuum cleaner draws a current of 2 A from the mains supply.

(a) What is the appropriate value of the fuse to be fitted in its circuit?

(b) What will happen if a 13 A fuse is fitted in its circuit?

Which of the following circuits will still be dangerous even if the fuse blows off and electric iron stops working during a short circuit?

An electric kettle rated as 1200 W at 220 V and a toaster rated at 1000 W at 220 V are both connected in parallel to a source of 220 V. If the fuse connected to the source blows when the current exceeds 9.0 A, can both appliances be used at the same time? illustrate your answer with calculations.

What is the main difference in the wiring of an electric bulb and a socket for using an electric iron in a domestic electric circuit? What is the reason for this difference?

Explain why, it is more dangerous to touch the live wire of a mains supply rather than the neutral wire.

Why is it safe for birds to sit on naked power lines fixed atop tall electric poles?

A domestic lighting circuit has a fuse of 5 A. If the mains supply is at 230 V, calculate the maximum number of 36 W tube-lights that can be safely used in this circuit.

What produces magnetism in the human body?

Name one medical technique which is based on magnetism produced in human body. For what purpose is this technique used?

Name two human body organs where magnetism produced is significant.

What is the full form of MRI?

Name of the technique by which doctors can produce pictures showing insides of the human body.

Name one technique which can detect cancerous tissue inside the body of a person.