What is current? Write its SI unit.

The rate of flow of charge is called current.
Its formula is    Current(I) =    Charge (Q) / Time taken (t)
Its SI unit is ampere(A)

What is Electric Circuit?

Electric circuit is a path made by connecting electric source, load and switch with a conducting wire in order to maintain a continuous flow.

Polarity

The relative orientation of poles; the direction of a magnetic or electric field, is called as polarity. It is +/- .

Alternating Current (AC)

The current whose polarity changes alternatively with time is called AC. It is generated from AC generator. It can be altered by transformers.

Direct Current (DC)

The current whose polarity does not change with time is called as DC. It is generated from battery or bicycle dynamo. It cannot be altered by transformers.

Effects of current

1.    Heating effect of current
2.    Lighting effect of current
3.    Magnetic effect of current
4.    Chemical effect of current

Heating effect of current

When electric current is passed through the conductor having high resistance, it gets converted into heat energy, which is called as heating effect of current.

What is heating element? Write any three features of Nichrome wire.

Heating element is the conductor that converts electrical energy into heat energy. Generally, nichrome wire is used as a heating element. It has high resistance and is made up of an alloy of nickel (60%) and chromium (40%). Its melting point is 1400 degree centigrade.
The features of nichrome wire are: -
•    It has high resistance.
•    It has high melting point
•    It does not react with oxygen of air even at the temperature of 900 degree centigrade.

Write down the applications of heating effect of current.

The main application of heating effect of current are :-
•    The heating effect of current is utilized in the heating appliances like electric iron, room heater etc.
•    An electric fuse is made on the basis of the heating effect of current.

What is the meaning that the frequency of alternating Current distributed in Nepal is 50 Hertz (Hz)?

The meaning of 50Hz is the polarity of the AC supplied changes 50 times per second.

What is lighting effect of Current? Write any two devices which are based on this effect.

When electric current is passed through a conductor having high resistance, the electrical energy is converted into heat and light energy. This is known as lighting effect of current. Filament lamp and fluorescent lamp are based on this effect of current.

What is filament? Name any three materials which are used for making filament.

Filament is a small coil of wire having very high melting point and very high resistivity which is used in lighting devices. The materials which are used for making filament are:-
•    Nichrome wire- an alloy of nickel (60%) and chromium (40%)
•    Tungsten wire
•    Manganin wire - an alloy of manganese (83%) copper (13%) and Nickel (4%)

Which filament is used in filament lamp?

Tungsten filament is used as the filament in this lamp.

Tungsten wire can't be used as a fuse wire.

Fuse is a safety measure in the electrical circuit so, it must have low melting point and resistance but tungsten wire has high melting point and high resistance so it can't be used as a fuse wire.

The tungsten filament becomes white hot while passing current through it but the copper wire connecting the filament does not why?

The tungsten filament becomes white hot because it has high resistance but copper wire has low resistance so, it does not become red hot.

Explain how filament lamp produces heat and light energy with diagram.

Filament lamp consists of a coil made up of tungsten metal called filament enclosed in a glass bulb. When current passes through the filament, it because very het and white because of its high resistance and hence radiates heat and light energy.

Give reasons:

a)    The filament of filament lamp is made up of tungsten metal. Write the features of tungsten metal.

It is because of the following features:
•    It has high resistance.
•    It has high melting point. (3400 degree Centigrade)

b)    An inert gas is filled in filament lamp.

Filament lamp contains filament made up of tungsten metal. If the filament comes in contact with oxygen gets destroyed due to oxidation therefore inert gases such as argon neon or inactive gases like nitrogen is filled in the filament lamp.

Explain how fluorescent lamp produces heat and light energy with a diagram.

The fluorescent lamp consists of long cylindrical glass tube filled with mercury vapor and the inner surface of the tube is coated with fluorescent powder.

There is an electrode on either side  of  the  lamp  such that electrons flow through mercury vapor from one electrode to the other.
 
When electricity is passed the electrons starts to flow through the mercury vapor and produces ultraviolet radiation. These UV rays are invisible but become visible when they collide with the fluorescent powder on the wall. In this way heat and light is produced.

Give reasons:

1. The fluorescent lamp of the power 60 watt gives more brightness than the filament lamp with the same power why?
   Filament lamp converts 10% of the electrical energy into light energy but fluorescent lamp converts 30% of the electrical energy into lights  energy.  So,  the  fluorescent lamp of the power 60 watt gives more brightness than the filament lamp with the same power.
2. Mercury vapor is filled in a fluorescent lamp.
   Mercury vapor is filled in a fluorescent lamp in order to produce - UV rays. In this process when electrons from cathode strike the mercury atoms, UV rays are produced.
3. Inner wall of fluorescent lamp is coated with fluorescent powder.
   Inner wall of fluorescent lamp is coated with fluorescent powder in order to produce visible light when UV- rays strike the mercury vapors.

Differentiate between filament lamp and fluorescent lamp.

What is magnetic effect of current? Describe a simple experiment to show magnetic effect of current.

When an electric current is passed through a wire, it becomes a temporary magnet. This is known as magnetic effect of current. This can be verified by the simple experiment. Consider thick card board paper and make a hole at its centre. Iron dust are scattered on the paper and a conductor is passed through the hole. When electricity is passed through the wire, the iron dust is attracted towards the wire. This proves that the wire changes into magnet when electricity is passed through it.

Study the given diagram and answer the following questions:

1. What does the following figure represent? Which effect of Current is shown by it?
   The given figure represents the deflection of magnetic compass when it is placed near a current carrying conductor. This figure represents the magnetic effect of current.
2. What will happen if the wire is disconnected from the battery why?
   If the wire is disconnected from the battery the magnetic compass will return to the original position because it will lose magnetic property in the  absence  of  electric field.
3. Write one use of this effect of current.
   The magnetic effect of current is used in different device such as electromagnetic crane, motor, electric bell, telephone etc.

Right hand thumb’s rule

It states that when the current carrying wire is grasped by the right hand in such a way the thumb is pointed towards the direction of current, the curl of the remaining four fingers, gives the direction of magnetic field.

What is solenoid? Write its use.

A solenoid is a long cylindrical coil of insulated wire having a large number of turns. It is used to produce a strong magnetic field from electric current. The spiral adjustment of the insulated wire, is called as solenoid. When electric current is passed through it, it becomes a magnet(temporary).

Right hand grip’s rule

It states that if the solenoid is gripped by the right hand in such a way that the fingers are in the direction of current flowing in the wire, the thumb will point the north pole of it. The opposite pole will be the south pole.

What is electromagnet? Explain why this is called as temporary magnet.

An electromagnet is a temporary magnet which is made by winding a coil of insulated wire around a piece of  magnetic  substance  like  iron nail. Electromagnet is also called as temporary magnet because the piece of magnetic substance like iron rod  used  to  make  electromagnet  shows the property of magnet when electricity is passed through it and it completely loses magnetic property when current stops flowing. When current is passed through the solenoid, it behaves as a temporary magnet, which is called as an electromagnet. 

Nowadays the use of electromagnet is increasing rapidly give any three reasons or writes any advantages of using electromagnet. Write the name of any three devices where electromagnet is used.

Nowadays the use of electromagnet is increasing because of the following useful properties of electromagnet:
•    It is temporary in nature so that it can be prepared to the necessitous desire.
•    The strength of the magnet can be changed according to the need.
•    The electromagnet of required shape and size can be made.
•    Electromagnet is used in several electrical appliances such as television, tape recorder, loudspeaker, electric bell, generator etc.

Write any three ways to increase the strength of electromagnet.

Some ways to increase the strength of the electromagnet are:
a.    By increasing the amount of current.
b.    By increasing the number of turns of the wire in the solenoid.
c.    By decreasing the distance between two poles like using U-shaped magnetic object.
d.    Using soft magnetic material in the core.

Study the given figure and answer the following questions.

1. What does the following figure represent?
2. Why the iron nails are attracted by the iron road?
3. What will be the position of iron nails if the batteries are removed from the circuit why?
4. Name any one of device based on this principle. Why insulated wire is used to make electromagnet? What will happen if the winding insulated wire is replaced by non- insulated wire.

1. The figure represents electromagnet.
2. When electricity is passed through the iron rod it acquires magnetic property so, the iron nails are attracted.
3. If the batteries are removed from the circuit, the iron nails will fall down because the magnetic property of the iron rod will be lost when current is cut off from the circuit.
4. Electric bell is based on this principle. The insulated wire is used to make electromagnet because the insulated wire stops the flow of current through the magnetic     substance     (e.g.      iron      nail)      and      prevents      short-      circuit. If the insulated wire is replaced by naked or non - insulated wire, current flows through the magnetic substance and short circuit occur. In such case, the magnetic substance is heated up instead of acting as an electromagnet

Write down any three main uses of electromagnets.

uses of electromagnet are:
1)    Electromagnets are used in the construction of electric bell, loud speakers, electric motors, electric fans etc.
2)    They are used to separate magnetic substances from non- magnetic substances.
3)    They are used to lift and transport heavy load like big machines, steel girders etc.

Give reasons:

a)    Soft magnetic materials are used for making electromagnets.
Soft magnetic materials are used for making electromagnets because such materials magnetize and demagnetize easily which is necessary for a temporary magnet.

What is electric bell? On which principle it is based? Draw  a  neat  and  labeled diagram of electric bell.
An electric bell is an electronic device which converts electrical energy into mechanical energy and then into sound energy. It is based on the principle of electromagnet.

Working principle of electric bell.

A    bell    works    with    the    principle    of    working    of electromagnetism. When the switch is pushed on, the circuit gets completed and the current starts flowing through the U-shaped electromagnet which creates a magnetic field in the core. This attracts the iron armature. When the armature moves towards the electromagnet, the hammer strikes the gong and the bell rings.

As the armature moves towards the electromagnet, the contact with the adjustment screw breaks which breaks the closed circuit and stops the current. Now,  when  there  is  no current there is no electromagnetism and the armature returns to the original position. This making and breaking of the circuit of the  electromagnet  continue  as  long  as  the button remains pressed.

Define magnetic flux.

Magnetic flux through a surface is defined as the number of magnetic lines of force passing though the surface held perpendicular to these lines of force.

Electromagnetic induction?

Electromagnetic induction is defined as the phenomenon by which electric current is induced in a closed coil due to the relative motion between the coil and a magnet. The emf thus produced is called induced emf.

Define induced current and induced emf.

The current produced in a conductor by electromagnetic  induction  is  called  induced current whereas the electromotive force produced by electromagnetic induction is called induced emf.

State the Faradays laws of electromagnetic induction.

Faradays laws of electromagnetic induction states that:
a)    Whenever the magnetic flux linked with a close circuit changes, an emf is induced in the circuit.
b)    The induced emf lasts as long as change in magnetic flux takes place.
c)    The magnitude of the induced emf is directly proportional to the rate of change of magnetic flux.

What is Generator? On which principle does it work? Write its types.

It is the device that converts mechanical energy into electrical energy. It is a device which is used to generate electricity in large scale on the basis of Faraday's law of electromagnetic induction. Types of generator are AC and DC.
Write any three methods to increase the magnitude of current in the generator.
a)    By increasing the strength of magnet.
b)    By decreasing the distance between coil and the magnet.
c)    By increasing the speed of rotation of the coil.

What is dynamo? On which principle does it work?

Dynamo is a device that convers mechanical energy into electrical energy. It is used to generate electricity in small scale on the basis of faraday's law of electromagnetic induction.

State Fleming’s right hand rule. What does it give? Explain with neat diagram.
Fleming’s right hand rule gives the  direction  of  induced emf. It states that when three first finger of right hand are held mutually perpendicular to each other in such a way that the thumb is placed in the direction of motion of conductor and the index finger is placed in the direction of magnetic field at that time the central finger gives the direction of induced current.

Describe the working mechanism of dynamo with figure.

Working: when the wheel of the bicycle rotates, the cap of the dynamo is made to rotate. This rotates the permanent magnet inside the dynamo. The coil of the wire crosses the magnetic lines of force due to the rotation (spinning) of the permanent magnet, that changes the magnetic flux. Thus current is induced in the coil. This current glows the bulb connected in the bicycle.

Study the given diagram and answer the questions that follow.

• What does  the  given  figure  represent?

          The figure represents the bicycle dynamo.

• On which principle it is based?

         It is based on the principle of electromagnetic induction.

• What will happen if the bicycle is moved faster? why?
  If the bicycle is moved faster, the magnitude of induced current increases because of increase in the rate of change of magnetic flux. Due to induction of high current, the headlight will glow brighter.
• Write any four ways to increase induced current.

          Ways to increase induced current are:
a.    By using powerful magnet.
b.    By Increasing the number of turns of wire in the coil.
c.    By Increasing the speed of rotation of the magnet.
d.    By decreasing the distance between the coil and the magnet.

What will happen if AC is supplied to the coil of dynamo?
When AC is supplied to the coil of dynamo it comes in motion. This is called as motor effect of current.

An AC generator is shown in the diagram. Study it and answer the following questions:

1.    Label A, B and C.
       A- armature , B- Slip rings C- Brushes

2.    What type of the conversion of the energy occurs here?

        Mechanical energy is converted into electrical energy.
3.    On which principle does it work?

       It works on the principle of electromagnetic induction.

4.    How does it differ with electric motor?

      They work in the reverse order that is generator converts mechanical energy into electrical energy whereas electric motor converts   

      electrical energy into mechanical energy.

5.    Write any four ways to increase the induced emf.

Four ways to increase its strength are:
o    Use of powerful magnet
o    Increase in the number of turns of a coil
o    Increase in the speed of rotation of the magnet
o    By decreasing the distance between the coil and the magnet.

What  is motor effect? State the device which is based  on   this   principle.

When a current carrying conductor is placed in a magnetic field, motion develops in it this is called as motor effect. Electric motor is based on this principle

What is electric motor? On which principle it is based? Write its application.

An electric motor is a device that converts electrical energy into mechanical energy. It is based on the principle of motor effect. It is used in domestic fan, washing machine, vacuum cleaner etc.

Differentiate between Generator and electric motor.

State Fleming’s left-hand rule.

Fleming’s left-hand rule states that if  the  first  three  fingers  of the left hand are held mutually perpendicular to each other so that index finger points to the direction of magnetic flux and the central finger points to the direction of electric current then at that time the thumb points the direction of motion of the conductor.

Inverter

An inverter converts the DC voltage to an AC voltage. In most cases, the input DC voltage is usually lower while the output AC is equal to the grid supply voltage of either 120 volts, or 240 Volts depending on the country.
The inverter may be built as standalone equipment for applications such as solar power, or to work as a backup power supply from batteries which are charged separately.

Battery charger

A battery charger,  or recharger,  is  a  device  used  to  put  energy  into  a  secondary  cell or rechargeable battery by forcing an electric current through it.

Solar panel

Solar panel is the group of photo cells. They convert light energy into electrical energy.

Adaptor

An adapter or adaptor is a device that converts attributes of one electrical device or system to those of an otherwise incompatible device or system. Some modify power or signal attributes, while others merely adapt the physical form of one connector to another.

Define transformer. On which principle it is based?

Transformer is a device which is used to changes the voltage of alternating emf. It is the device that converts high AC voltage into low and vice versa. This is based on the principle of mutual induction.

Transformer

Transformer is the device which is used to convert low AC voltage into high or vice-versa.

There are two types of transformer
a)    Step up transformer

b)    Step down transformer

State two laws in which the transformer is based:

The transformer is based on the following two laws:
1.    The input energy is always equal to the output energy in a transformer,
2.    The voltage is directly proportional to the number of turns of the wire.

What is mutual induction? Explain how transformer works.

Mutual induction is the process of developing or inducing current in the neighboring coil whenever the current or magnetic flux through a coil changes. When an AC flows through the primary coil there is change in magnetic flux around the core. This activates the electrons of the secondary coil where by an emf is induced. Then the electrons flow in the secondary coil giving rise to secondary Voltage.

Define input current and output current.

The current that flows into a transformer is called input current whereas the current that flows out of a transformer is called output current.

Define primary voltage and secondary voltage.

The potential difference of input current in any transformer is called primary voltage and the potential difference of output current is called secondary voltage.

Uses of transformer

• The transformer is used in voltage regulators of television, computer, air conditions etc.
• The most important use of transformer is in the transmission of alternating current over long distances.

Write different losses that occur in a transformer.

Different losses of a transformer are as follows:-
•    Copper loss/ heat loss: - Since current flows in a copper wire in transformer due to resistance of the copper wire heat is produced. This heat produces brings a loss of energy.
•    Iron Losses: - Induced current is developed in the iron core of the transformer called eddy current and the energy is lost in the form of heat. This is called as iron loss.
•    Magnetic loss: - The entire magnetic flux produced by the primary coil does not flow through the secondary there by allowing a certain amount of energy supplied to the primary to go waste.
•    Hysteresis losses: The core of the transformer is taken through a cycle of magnetization as many times per second as  the  frequency  of  the  A.C.  supply.  In each cycle certain amount of energy is lost this is called as hysteresis loss.

Explain why the voltage of direct current cannot be altered by the transformer?

Direct current can't be altered by the transformer because there is no fluctuation in the direct voltage so that no change in magnetic flux in the coil and hence the emf is not produced in the secondary coil.

The use of alternating current would be limited if transformer was not invented. Justify the statement with two clues.

Transformer is used to convert low AC voltage into high AC voltage and Vice-versa. The use of alternating current would be limited if the  transformers  were  not invented. Any two clues to justify the statements are:-
•    The conversion of low AC voltage to high AC voltage in the power station would not be possible.
•    All the electrical appliances that require low AC voltages cannot be operated.
•    The transmission of electricity in the transmission line would not be possible.

Give reasons:-

a)    The core of the transformer is laminated.
Due to the rapidly changing magnetic flux eddy current is developed in the core of the transformer, if the cores of the transformers are not laminated this current produces here eddy current resulting heat. So, to prevent the damage of the transformer and loss of energy of the transformer the core is laminated.

b)    The core of the transformer contains large number of sheets instead of a single block.
If the core of a single block of iron is used instead of many laminated sheets, there will be more heating effect and less output will be obtained.

c)    Soft iron is used to make the core of the transformer.
The leakage of the magnetic flux through the coil when the current gets induced in the secondary coil is minimum when soft iron is used to make core, so, soft iron is used to prevent energy loss.

d)    The number of turns in the primary coil and secondary coil of a transformer are never made equal.
Transformer is used to convert the emf of AC voltages according to the number of turns. If the number of turns of the secondary coil  is  greater  than  the  primary turns, low Ac voltage will be changed into high AC voltage and if the turn is less high AC voltage will be changed into low AC voltage. So, if the no of turns is equal there is no change in voltage i.e. no meaning  of  transformer  so,  the  number  of turns in the primary coil and secondary coil  of  a  transformer  are  never  made equal.

Electric power

The electric power of a device is the rate at which it converts electrical energy into other forms of energy.
Electric Power(P) = Workdone/time taken
Its SI unit is watt(J/s) 1kW=1000W
1MW=1000000W
1HP=746 W(approx.)

The power of a bulb is 60watt. What do you mean by this?

The power of a bulb is 60 watt. It means it can convert 60 joules of electrical energy into heat and light energy in one second.

Electric Power(P) = Current(I) x Potential difference(V)

Numerical
If an electric heater of voltage 220 v consumes 20A electric current, what is its power?

Given,
Potential difference(v) = 220 v

Current (I) = 20A
Power (P) = ?

We have,
Power (P) = I x v
Or, P = 20 x 220 watt Or, P = 4400 watt

Hence, the electric power of the heater is 4400 watt.

 Chemical effect of current

When electric current is passed through the electrolyte, it undergoes some chemical changes, which is called as the chemical effect of current.

Electrolyte

An electrolyte is a compound that is capable of conducting the electricity. It undergoes chemical change when electricity is passed through it.

Electrolysis

It is the process of decomposition of an electrolytic solution into their respective ions by the passage of electricity.

Electroplating

It is the process of coating one metal by another by the process of electrolysis. 

Anode = Connected with positive terminal of battery

Cathode = connected with negative terminal of the battery

Conditions
a)    The metal where electroplating is being done should be connected as cathode.
b)    The salt solution of anode must be taken as an electrolyte.