Chapter 2 MAGNETIC EFFECT OF ELECTRIC CURRENT

The two properties of magnetic field

Lines are:

(a) the field lines start with the north

pole of the magnet and ends at the south pole of the very same.

(b) the closer the field lines will be

the stronger will be the magnetic

field.

The two ways are :

(a) with the help of a compass, as it always indicate the north pole.

(b) it can be traced by sprinkling iron dust.

As we know, the magnetic field is Stronger where the field line is Closest. So the area with the Closest field line in the given Pattern have the strongest Magnetic field.

False

The two axis do not coincide with each other as they are separated by an angle of about 17 degree.

A compass needle is a small bar magnet. when it is brought near to another bar magnet their field lines interact with each other.

Hence, the compass needle shows deflection.

To keep the door closed properly manufacturers use a strip of magnets at the doors of refrigerators.

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

north , south

The earth's magnetic field is rather like of a ......... magnet with its ......pole in the northen hemisphere

bar, south

The field lines begins with north pole and ends at south pole.

The area in which the force of magnet is exerted is called magnetic field line to determine the magnetic field line direction you to place a compass on a plane the direction of the needle of a compass shows the north pole, and so will be the direction of the magnetic field line which begins with the north pole and end at south pole.

As a matter of fact the resultant of forces at north pole can only be in one direction. But if magnetic field lines intersect each other then the north pole will show resultant forces in two direction, which is not possible.

This is because, the field produced is very weak.

A magnetic field lines are lines which are drawn around the magnet and which always starts with the north pole and ending at the south pole.

Activity:

> to draw a magnetic field line around the bar magnet.

> take a bar magnet and a compass and place them on a plane over a hard sheet.

> the boundary of the marker should be marked.

> Place the compass near the north pole of the magnet. The south pole of the needle points towards the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet.

> mark the both end of the needle.

> now move the needle to a new position such that the previously occupied north position should now occupy the south position and vice versa.

> continue this process till you the south pole of the bar magnet.

> now by joining all the points by a curve will represent the magnetic field line.

The earth itself act as a magnet .and its geographical north is in south pole and the geographical south in north pole .so a freely suspended magnet always points in north-south direction.

This is because magnet exert force in every direction.

the magnetic field line always originates from the north pole and ends at south pole.

because brass is an alloy.

magnetic field line never intersect each other.

geographical south is in the north pole.

15°

bar magnet.

Iron and steel shows magnetic behaviour

The plotting compass is placed near the south pole of a bar magnet. The pointer of plotting compass will point at right angles to the south pole.

The metallic pointer of a plotting compass get deflected only when it is placed near a bar magnet because the pointer has permanent magnetism.

The strength of field is zero, when the magnetic field lines are equidistance and parallel.

As the needle of the compass is tending to move toward the other end of the bar magnet, so the nearer end will show the north pole and the other end will show the south pole.

Arrows shows the direction due to the deflection.

As the

As we see in the figure, the pointer is pointing away from the magnet. It means X is the NORTH POLE

A=N, B=N, C=S, D=S, E=N, and F=S.

The field lines originate from the north pole and end at the south pole.

(i) S-N, N-S

The field line always emits form the north pole and ends at the south pole.

(ii) Magnet 2 is the weaker magnet.

It has small magnetic field.

magnetic effect of a current can be utilised in detecting a current carrying wire cancelled in a wall.

By the deflection of a compass needle, when placed near a current carrying wire gives a conclusion that there is a magnetic field produced around the wire.

Oersted, was the scientist who first discovered the magnetic effect of current.

The magnetic field become very strong when the iron core is inserted into a current carrying conductor.

The rule for finding the direction of magnetic field produced by a straight current carrying conductor was given by Maxwell’s right hand thumb rule.

A concentric circle is formed around a straight current carrying conductor and its centre lies in the conductor.

Maxwell’s corkscrew rule is the other name for the Maxwell’s right-hand thumb rule.

True, Inside a long circular coil carrying current the magnetic field lines are always parallel with each other.

A current carrying conductor is of solenoid shape whose magnetic field pattern seems to that of the bar magnet.

The three ways are :-

(1) By increasing the number of turns in the coil.

(2) Increase the current flow in the coil.

(3) The air gaps between the poles should must be reduced.

(a) Magnetic field, concentric circles

(b) Bar magnet

(d) Turns, current, coil

(e) North pole

(f) South pole

Explanation: (a) a concentric circle is formed by the lines of a straight current carrying conductor.

(b) when current is passes through a solenoid it starts to act as a bar magnet.

(d) by increasing the no. of turns or increasing the flow of current or inserting the coil in a core the magnetic effect can be increased.

(e) north pole is the direction, if a coil is viewed from one end and the flow of current is in anticlockwise direction.

(f) when the current flow direction is clockwise when view from one end of the coil then that end is south pole.

To locate a current carrying wire concealed in a wall one should use a plotting compass. by moving plotting compass on the wall the deflection in its needle shows the place where wire is concealed in the wall.

let us take a copper wire AB on a plane such that it faces North-South. Now place a plotting compass under it. connect both end to a battery with a switch to put it on and off.

When the switch is on then the plotting compass needle shows deflection. When its turned off then the compass stop showing any deflection. This shows that the magnetic field is associated with electric field.

The Fleming's left rule is used to determine the direction of magnetic field around a straight current-carrying conductor. According to the rule,

The F(Thumb) represents the direction of Force of the conductor
The B(Forefinger) represents the direction of the Magnetic field
The I(Centre finger) represents the direction of the Current.

Maxwell’s right hand thumb rule. According to this law if we hold our thumb of right hand in the direction of magnetic field and close our finger then our enclosed finger shows the magnetic field line around the conductor.

Let AB be a straight wire. Placed vertically A to B. To find the direction of magnetic field we assume that we are holding the current carrying wire in such a way that our thumb of right hand shows the direction of flow of current. Then the finger enclosing the wire. The direction in which our finger is enclosed shows the direction of magnetic field which is anticlockwise.

Maxwell’s right hand thumb rule is also known as Maxwell’s corkscrew rule. It is used to find out the direction of magnetic field along a straight current carrying conductor.

There are two ways of doing this :-

(1) must increase the number of turns of the coil.

(2) Must increase the current flow in the coil.

According to this rule, we first look at one face of the coil and if the current through the coil seems to be flowing in the clockwise direction, then that face is considered as the South pole. And if the current seems to be flowing in the anti-clockwise direction, then the face of the coil is considered as the North pole.

a) For this face of the coil, the current is flowing in the clockwise direction, so it acts as South-Pole.

b) For this face of the coil, he current if flowing in he anti-clockwise direction, so it acts as North-Pole.

It depends on following factors:-

i) Current: Larger he current, stronger will be the magnetic field.

ii) Number of coils in the solenoid: Greater the number of coils in the solenoid, stronger will be the magnetic field produced.

A coil C of insulated wire is wound around the soft iron core and the two ends of the coil are connected to a battery. This is how an electromagnet is made.

Electromagnetic cranes are used to separate copper from iron in a scrap yard. Switch in on the curen energises the electromagnet, thus producing magnetic field. This magnetic field attracts the iron pieces, thus separating them from the copper.

An electromagnet produces a temporary magnetic field which sustains till the current flows through the coils of the electromagnet, while a permanent magnet produces a permanent magnetic field.

Electromagnets are used in Electric bell and Electric motors.

Permanent magnets are used in Refrigerators doors and Toys.

A solenoid is a long coil containing a large number of close turns of insulated copper wire.

The magnetic field produced by a current carrying solenoid is similar to that produced by a bar magnet.

Magnetic field lines inside a current carrying conductors are in the form of parallel straight lines.

Following are the three ways of increasing the strength of the magnetic field of current carrying solenoid:

i) Increasing the current flowing through the coil of solenoid.

ii) Increasing the number of turns in he solenoid.

iii) Using soft iron core in he solenoid.

Soft iron core should be used.

An electromagnet is called a temporary magnet because it produces magnetic field lines only when the current flows through the coil of the electromagnet. When we stop the current through the coil, the magnetic field lines diminishes.

Soft iron core is used in the electromagnets because it loses all its magnetism when the current through the coil stops flowing. While in case of steel, there is still some magnetism even after the current stops flowing through the coil of electromagnet.

The strength of electromagnet depends on the following factors:

i) Number of turns in the coil: Increasing the number of turns in the coil increase the strength of magnetic field produced by the electromagnet.

ii) Current flowing through the coil: Increasing the current flowing through the coil increases the strength of magnetic field produced.

iii) Length of air gap between its poles: Decreasing he length of air gap between the poles of electromagnet increases the strength of electromagnet.

An electromagnet is a temporary magnet which works on the magnetic effect of the current. It consists of long coil of insulated copper wire wound around a soft iron core and he two ends of he coil are connected to a battery. As the current flows through the coil, the magnetic field lines ae produced. These field lines sustains till the current continues to flow through the coil of electromagnet.

Electromagnets are used in several devices such as Electric bell, Electric motors, Loudspeakers, etc. They are also used by doctors to remove iron or steel particles from patient’s eyes and to remove iron pieces from wounds.

the strength of the magnetic field between the poles of an electromagnet would be unchanged if the direction of current in electromagnet winding were reversed.

the diagram represents the magnetic field caused by a circular current carrying conductor.

the magnetism inside a long straight solenoid remains same at every point.

the magnetic field near a long straight wire consists of concentric circles centred on the wire.

the north-south polarities of an electromagnet can be found easily by using clock face rule.

the direction of current in the coil at one end of an electromagnet is clockwise then that end is south pole.

the direction of electric current is anticlockwise when viewed form the north pole.

soft iron is mostly used for making the core of the electromagnet.

the magnetic effect of the current was discovered by Oersted.

when soft iron bar is inserted inside a current carrying solenoid then it increases the magnetic field inside the solenoid.

the magnetic field lines in the middle of the current carrying solenoid are parallel to the axis of the tube.

When the front face of a circular wire carrying current behaves like north pole ,then the direction of current in this field is anticlockwise.

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

(a) Clockwise would be the direction of magnetic field in wire A.

(b) the direction of the magnetic field in the wire B is anticlockwise.

Maxwell’s right hand thumb rule.

According to the fig. end a is the south pole as the direction of the current flow is clockwise from this end.

The direction of the current flow is anticlockwise. This can be determined by using Maxwell’s right hand thumb rule.

(a) End A becomes south pole. This is because from the end at the current flows in clockwise direction.

(b) The movement of the compass needle is away form the end B. As end B is the north pole.

According to the Maxwell’s right hand thumb rule the direction of the magnetic field will be in clockwise direction.

The easy way to find the polarity is right-hand rule: " If the current flows in the direction of your fingers, the thumb points towards the north pole".

If we assume an electromagnet which has two ends i.e. X and Y, then,

(a) South is the polarity of end X as direction of current flow from that end is clockwise.

(b) The end Y will be the north pole as the current flow from this end shows the anticlockwise direction.

(c) The rule used here to find the polarity of the ends is clock face rule. According to this rule if the face from where it is being observed is showing the flow of current in anticlockwise direction then that end is N-pole but if the same face shows the flow of current in a clockwise direction then that end becomes S-pole.

East to west will be the direction of the current.

According to the Maxwell’s right hand thumb rule if the enclosed fingers shows the direction of the magnetic field then the thumb will always point in the direction of current flow.

(a) the current should be passed from top to bottom to produce a clockwise magnetic field around the conductor.

the direction desired to pass the current is upward.

The magnetism produces in the human body is because of ionic current flowing in the human body.

(MRI) Magnetic Resonance Imaging is the technique based on magnetism procedure in human body. This is used to get image of the internal parts of the body.

Brain and Heart are two parts where magnetism is being used for the treatment .

The full form of (MRI) is Magnetic Resonance Imaging.

The technique used by doctors to produce inside pictures of human body is called MRI.

MRI can detect the cancerous tissues inside the human body.

When a conductor is placed in a magnetic field then a mechanical force is exerted on the conductor, which eventually make the conductor move.

The force experienced by a current carrying conductor is largest when it is placed at right angle in a magnetic field.

(a) By Fleming’s left hand rule direction of centre finger represent the current.

(b) Direction of the forefinger in the Fleming’s left hand rule represents the magnetic field.

(c) Force acting on the conductor is represented by the direction of thumb in Fleming’s left hand rule.

The device which work on the magnetic effect of current is electric bell. Electric bell works when electromagnetism is produced.

Electrical motor is used to convert electrical energy in to mechanical energy.

A motor converts electrical energy into mechanical energy. So the two forms are electrical and mechanical.

False, because electric motor is used to convert electrical energy in to mechanical energy.

The three things that are 90° to each other, and next to each, and next to each one are:-

Current- it is denoted by the direction of the centre finger.

Magnetic field- ii is denoted by the direction of the fore finger.

Force or motion- it is denoted by the thumb.

Commutator is used to reverse the direction of current in the coil of a motor.

Commutator is the other name for the split ring which is used in the coil of a motor.

Its function is to reverse the current every time it reaches the vertical position in the coil.

The brushes of an electrical motor are made of carbon.

The core of the coil of an electric motor is made of soft iron.

The part of the electric motor which remain fixed is brush and the part which rotate with the coil is commutator.

Every time in a revolution when the coil passes the vertical position the split ring is there to reverse the current.

(a) Left

Fleming’s rule for the motor effect uses the left hand.

(b) Commutator; rotation

a motor contains a kind of switch called a commutator which reverse the current every half rotation.

Fleming’s left hand rule can be used to find the direction of force acting on the conductor.

The two ways are:-

(1) by increasing the flow of current.

(2) by increasing the strength of the magnetic field.

Electric motor is the device whose working depends on the force exerted by a current carrying conductor.

Fleming’s left hand rule says that the centre finger shows the direction of the current, the fore finger represents the direction of the magnetic field and the thumb shows the direction of force or motion.

The principle on which the electric motor work says that if a rectangular current carrying coil is placed in a magnetic field, a force act on it which make it to rotate continuously.

Some of the devices using electric motors are:- electric fans, washing machine, mixer, grinder, etc.

To make the coil rotate continuously in the same direction, the current to coil in most of the d.c motor reversed twice during each rotation.

The device which reverse the current is known as commutator.

(i) When the current were reversed then in that case the rotation of the motor would be reversed.

(ii) When the magnetic field were reversed then in that case the rotation of the motor would reverse.

(iii) When both the current and magnetic field were reversed simultaneously then in that case the rotation of the motor remains same or unchanged.

To make a motor more powerful it is necessary to increase the number of turns on the coil in the motor.

It is device used for the conversion of electrical energy in to mechanical energy.

The working of a simple electric motor

Initially, the coil ABCD is in the horizontal position. On pressing the switch, current enters the coil through carbon brush P and commutator half ring X. The current flows in the direction ABCD and leaves via ring Y and brush Q. The direction of magnetic field is from N pole to S pole of the magnet. According to Fleming's left-hand rule, the force on sides AB and CD is in the downward and upward directions respectively. This makes the coil ABCD move in the anticlockwise direction.

When the coil reaches vertical position, then the brushes P and Q will touch the gap between the two commutator rings and current is cut off. But the coil does not stop rotating as it has already gained momentum. When the coil goes beyond the vertical position, the side CD comes on the left side and side AB comes to the right side, and the two commutator rings change contact from one brush to the other. This reverses the direction of current in the coil, which in turn reverses the direction of forces acting on the sides AB and CD of the coil. The side CD is pushed down and side AB is pushed up. Thus, the coil rotates anticlockwise by another half rotation.

The reversing of current in the coil is repeated after every half rotation due to which the coil (and its shaft) continues to rotate as long as current from the battery is passed through it. The rotating shaft of electric motor can drive a large number of machines which are connected to it.

the special features of commercial electric motors are:-

i. the coil is wound on a soft iron core. This increases the strength of magnetic field, which makes the motor more powerful.

ii. the coil contains a large number of turns of insulated copper wire.

iii. a powerful electromagnet is used in place of permanent magnet.

In an electric motor, the direction of current in the coil changes once in half rotation.

The direction of force acting on the electron beam will be into the page.

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 90°

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 180°.

A current flows in a wire running between the S and N poles of a magnet lying horizontally then the force on the wire due to the magnet is directed vertically downward.

An electric motor is a device which transform electrical energy into mechanical energy.

A magnetic field exert force on a stationary electric charge.

The direction of the force on the wire due to the magnet is vertically upwards.

Clockwise direction is observed when seen form above. this can be observed by the Fleming’s left hand rule.

The direction of the wire is to move in the upward direction by the virtue of Fleming’s left hand rule.

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

The movement of the wire is in the downward direction, by the virtue of Fleming’s left hand rule.

The force on a current carrying wire that is parallel to a magnetic field will be zero.

This is because the magnitude of force depends on the sin of the angle between the direction of current and the direction of magnetic field, so if the current carrying wire is held parallel to the magnetic field, the force will be zero.

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, will be positively charged.

The device which converts mechanical energy into electric energy is electric generator.

(a) D.C generator uses split rings.

(b) A.C generator uses slip rings.

The phenomenon which is made use of in an electric generator is electromagnetic induction.

the rule which gives the direction of induced current is Fleming’s left hand rule.

A relative motion between the wire and the magnet is necessary for the production of current by electromagnetic induction.

A.C. generator (or Alternator) is used at Power Stations.

change should be made in an a.c. generator so that it may become a d.c. generator is :-

1) replace the slip rings of an AC generator by a commutator.

(a) True, Electromagnetic induction is necessary for the working of a generator.

(b) False, Electromagnetic induction principle is for electric generator but not for motor.

To transfer the current from coil to load is the function of brushes in the electric generator.

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

When current is 'switched on' and 'switched off' in a coil, a current is induced in another coil kept near it. this phenomenon known as Electromagnetic induction.

The major difference between the simple alternator and most practical alternators is,

Simple alternator: Magnet fixed and coil rotates; Practical alternator: Coil fixed and magnet rotates .

To obtain water for making steam for turning turbines and for cooling spent steam to condense it back into hot water for making fresh steam Thermal Power Stations usually located near a river.

Three sources of magnetic fields are, Permanent magnets; Electromagnets ; Conductors carrying current (such as straight wire, circular coil and solenoid carrying current) .

A generator with commutator produces direct current.

If the current in coil A is changed then Yes, some current will be induced in the coil B because of change in magnetic field through the coil B due to change in current in coil A. This is called electromagnetic induction.

when a straight conductor is moved in a magnetic field, then current is induced in the conductor is the principle on which electric generator works.

two ways in which the current induced in the coil of a generator could be increased are:-

(i) by rotating the coil faster

(ii) by using a coil with a larger area

DC flows in one direction only while AC reverses direction after equal intervals of time is the difference between alternating current and direct current and also,

(i) DC current remains same with time in its value and direction.

(ii) AC current changes with time and changes its direction every time after a certain interval of time.

(i) A dry cell gives dc current.

(ii) A Power House generator gives ac current.

Fleming’s right hand rule gives the direction of induced current produced in a straight conductor moving in a magnetic field.

According to Fleming's right hand rule: Hold the thumb, the fore finger and the centre finger of your right-hand at right angles to one another. Adjust your hand in such a way that forefinger points in the direction of magnetic field, and thumb points in the direction of motion of conductor, then the direction in which centre finger points, gives the direction of induced current in the conductor.

(a) current induced in a coil due to its rotation in a magnetic field is stated by Fleming’s right hand thumb rule.

(b) Force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it is stated by Fleming’s left hand rule.

The construction of an A.C. generator differs from a D.C. generator in the following ways:-

High pressure steam normally drives the alternators in a Thermal Power Station.

Fuels can be used to heat water in the boiler are Coal; Natural gas; Oil.

Construction:

AC generator consists of a rectangular coil ABCD which can be rotated fastly between the poles N and S of a strong horseshoe-type permanent magnet M. The coil is made of a large number of turns of insulated copper wire. The two ends A and D of the coil are connected to two circular pieces of copper metal called slip rings R1 and R2. As the slip rings rotate with the coil, the two fixed pieces of carbon called brushes, B1 and B2, keep contact with them. So, the current produced in the rotating coil can be tapped out through slip rings into the carbon brushes. The outer ends of carbon brushes are connected to a galvanometer to show the flow of current in the external circuit.

Working:

Let us assume the coil ABCD, which is at the start in the horizontal position, is rotated in the anticlockwise direction. The side AB of the coil moves down and side CD moves up. By virtue of this, induced current is produced in both the sides, which flows in the direction BADC (according to Fleming's right hand rule). Thus, in the first half rotation, the current in the external circuit flows from brush B1 to B2. After half revolution, sides AB and CD will interchange their positions. So, side AB starts moving up and side CD starts moving down. As a result, direction of induced current in the coil is reversed and flows in the direction CDAB. The current in the external circuit flows from brush B₂ to B₁.

The term "electromagnetic induction refers to the production of electricity from magnetism is known as electromagnetic induction.

a device which works on the phenomenon of electromagnetic induction is Electric generator.

current can be induced in a coil of wire through these ways:-

(i) by moving the coil relative to a fixed magnet

(ii) by keeping the coil fixed and moving a magnet relative to it.

In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.

some sources of direct current and some of alternating current are:-

Dynamo, solar cell, batteries. Etc. (direct current).

Hydroelectric power plant, electric generator, etc. (ac current)

changes direction periodically in ac occurs but this is not possible with dc.

The frequency of A.C. supply in India is 60HZ.

A rectangular coil of copper wire is rotated in a magnetic field the direction of induced current changes once in each half revolution.

The phenomenon of electromagnetic induction is producing induced current in a coil due to relative motion between a magnet and the coil.

The device used for producing electric current is called a generator.

The essential difference between an AC generator and a DC generator is that AC generator has slip rings while the DC generator has a commutator.

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 return to zero.

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 moving out of the solenoid.

An electric generator converts mechanical energy into electrical energy.

A d.c. generator is based on the principle of electromagnetic induction.

The magnitude of induced current does not depend on the resistivity of the wire of the coil.

The frequency of direct current (d.c.) is 0 Hz.

The frequency of alternating current (a.c.) supply in India is 50 Hz.

(a) when the N-pole is removed the galvanometer is deflected to the left.

(b) the S-pole is inserted the galvanometer is deflected to the left.

(c) when the magnet is at rest in the coil No deflection in galvanometer is absorved.

three ways of increasing the deflection on the galvanometer are:-

1) Increase the number of turns in the coil.

2) Use a stronger magnet.

3) Increase the speed with which magnet is pushed into the coil (or removed).

(i) The name of the effect being produced by the moving magnet is electromagnetic induction.

(ii) When the magnet is moving away from the coil the needle of the galvanometer get deflected to left.

(iii) Large deflection to right occurs more quickly when the magnet is moved towards the coil at a great speed.

State two changes you would notice in the reading on the galvanometer.

two changes you would notice in the reading on the galvanometer are:-

1) it deflects toward left.

2) And it gets deflected towards right when the magnet is moved toward the coil at a great speed.

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

(a) when the current increased

(b) moving the wire upwards rather then downward will reverse the Current.

(c) the current will be increased by using a strong magnet.

(d) by holding the wire still in the magnetic field will increase the current.

(e) when the wire is moved parallel to the magnetic field then the current is zero.

(i) When a current is passed through coil B by plugging the key then the Galvanometer pointer moves to one side showing that a current is induced in the coil.

(ii) When the current is stopped by removing the plug from the key, Galvanometer pointer moves to the other side showing that the direction of induced current has been reversed. The phenomenon involved is known as electromagnetic induction.

Explain your answer mentioning the name of the phenomenon involved.

When a portable radio has a built-in transformer so that it can work from the mains instead of batteries then it will cause the step down to the transformer which may cause reduction in voltage.

Electric fuse is the name given to the device which automatically cuts off the electricity supply during short-circuiting in household wiring.

i) the usual capacity of an electric fuse used in the lighting circuit is 5A.

ii) in the power circuit of a small house the usual capacity of an electric fuse used is 15A.

(a) False

The green wire indicates the wire is grounded.

(b) False

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

Earth wire is used along with live wire and neutral wire, a third wire is also used in domestic electric wiring.

Red wire - Live wire

Black wire - Neutral wire

Green wire - Earth wire

0 volt is the electric potential of the neutral wire in a mains supply cable.

we know that,

I=p/v

So, by putting the values in the formula, we get

I= 180/240= 0.75A.

Fuse wire should must with stand only little more amount of current then 0.75A. so the required fuse is of 1A.

when live wire and neutral wire come in contact with each other then in that case electric short circuit occur.

To operate the lights in an A.C housing circuit the switch is introduced with the live wire.

In housing circuit the fuse wire is connected in series.

Red, Black and Green are the three different colours of wire generally used in an electrical appliances.

(a) The usual colour of the insulation of the live wire is red.

(b) The neutral wire is generally insulated with black colour.

(c) Green is the colour generally used for insolation of earth wire.

The main purpose of providing earthing in an electrical appliances is to avoid the risk of electric sock.

The two reasons why different electrical appliances in a domestic circuit are connected in parallel are:-

1) Because of the parallel connection it is possible to use one application while the other is switched off.

2) Voltage remains same throughout in case of parallel connection.

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

(a) In the main circuit a fuse should always be connected with the live wire.

(b) The body of an appliances should always be connected with the earth wire.

Tin-platted copper wire is used to manufacture the fuse. Because it has low melting point.

The melting point of the copper wire is very high so it is not used as a fuse wire. That is because it will not allow the breakdown of the fuse wire which is not advisery.

Cartridge fuses are used in electrical appliances like car stereos.

This type of fuse consist of consists of a glass tube T having a thin fuse wire sealed inside it. The glass tube has two metal caps at its two ends. The two ends of the fuse wire are connected to these metal caps. These are there for connecting the fuse in the circuit in a suitably made bracket.

when live wire and the neutral wire came in contact with each other then short circuit happens.

On the other hand when too many electrical appliances of high power rating are switched on at the same time or are connected to a single socket, they draw extremely large amount of current. This is known as overloading.

A fuse cuts off current when the current exceeds a safe value (due to short circuiting or overloading). When the current becomes large, it heats the fuse wire too much. Since the melting point of fuse wire is low, it melts and breaks the circuit. Thus, current in the circuits is cut off.

Let us assume the number of bulbs be y.

Power of y bulbs, P=60y

V=220V, I=5A

We know that

P = VI

60y = 220 x 5

60y = 1100

y=18.33

So, number of bulbs required are 18.

(i) fuse is used for the purpose of protection, and mainly used for avoiding the short circuit.

(ii) it is very important as it reduces the risk of electric sock, when live wire accidently touches the metal.

(a) (i) the max. current, I= PV

So, 3.260A is the max current.

(ii) the number of units of electricity it would use in 30 minute is E= P*t

So, 0.75KW*0.5h= o.375KWh.

the fuse rating suitable for this electric iron should be 5A.

the function of an earth wire is, When the live wire of a faulty appliance comes in direct contact with its metallic case, which has been earthed, the large current passes directly to the earth without passing through the user's body. Thus, it is necessary to earth the metallic bodies of electrical appliances so as to avoid fatal electric shocks.

given, P = 3kW = 3000W

V = 240V

P = V x I

I = P/V

= 3000/240 = 12.5 A

12.5A would be the required current.

The size of the fuse in a geyser circuit is 13A.

It is there to protect the whole wiring in case of short circuit.

The device used in place of the fuse is MCB.

the two hazards associated with the use of electricity are:-

1) one may get electric sock if he touches the live wire.

2) Electrical fire can occur due to the short circuiting because of overloading.

the important precautions which should be observed in the use of electricity are:-

1) Wires used should be good.

2) Proper earthing and fuse should must be used.

3) Electric appliances should be used only if they are dry.

We will switch off the main switch immediately so as to cut off the electricity supply if we see a person coming in contact with a live wire.

Electric switches should not be operated with wet hands because it may risk to electric sock.

At the time of short circuit, the current in the circuit increases heavily.

A 1.25 kW heater works on a 220 V mains supply. current rating suitable for the fuse would be 10A.

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 30.

In normal use, a current of 3.5 A flows through a hair dryer. The fuse required should be of 5A.

Switches, fuses and circuit breakers should be placed in the neutral wire 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 5A.

A 13 A fuse is the most appropriate value to use when 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.

The correct fuse for the TV set is of 2A when consumes an electric power of 230 watts and runs on 230 volts mains supply.

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

An MCB which cuts off the electricity supply in case of short-circuiting or overloading works on the magnetic effect of current.

Given: P=3.2kW=3200W, Fuse current rating=10 A, V=220 V

We have

P=VI

3200 = 220 x I

I=14.54 A

The required current is 14.54A and the rated current is 10A for the fuse, so the breakdown will take place.

Given, P₁=60 W, P₂=1200W, P₃=500W

Fuse rating = 10A

V=220V

We have, P=VI

Total power=60+1200+500=1760W

Therefore, 1760=220xI

I=8A

No, the fuse is of desired specification so it it will work properly.

(a) the appropriate value of the fuse to be fitted in the circuit is 3A.

(b) if a 13 A fuse is fitted in its circuit, short-circuiting or overloading occur which can damage the vacuum cleaner.

Circuit A is not dangerous after fuse blows because fuse is in live wire so it will cut the connection; Circuit B is dangerous even if fuse blows because the fuse is in neutral wire .

Given, P₁=1200W, P₂=1000W

V=220V

Fuse rating=9A

We know, P=VI

Total current required,

I = P/V

= (P₁+P₂)/V

= (1200+1000)/220

= 10A

The fuse will get burnt if both the appliances are switched on together. So one should not use both the appliances at the same time.

There is No earth connection for electric bulb but for the electric iron;

The reason for this difference is, earth connection given to socket for electric iron

it is more dangerous to touch the live wire of a mains supply rather than the neutral wire because Live wire at high potential of 220 V on the other hand Neutral wire is at ground potential of 0 V.

It is safe for birds to sit on naked power lines fixed atop tall electric poles because bird's body is not connected to the earth, so no current flows through bird's body into the earth.

Let the maximum number of tube-lights be y.

Power of y tube-lights, P=36y

V=230V, I=5A

We know that

P = VI

36y = 230 x 5

36y = 1500

y=31.94

So, number of tube-lights required are 31.