Electricity

What is SI unit of charge?

Coulomb. 1 Coulomb = 6.25 × 10¹⁸ electrons. Charge on 1 electron = 1.6 × 10^-19

What is electric current?

An electric current is defined as the charge flowing through any cross section of a conductor for a unit time.

Define 1 ampere

The electric current flowing through a conductor is said to be 1 ampere if 1 couloumb electric charge flows through any cross section of the conductor for 1 second.

Name the device that is used to measure electric current. How is it connected in the circuit?.

The device that is used to measure current is ammeter. It is always connected in series in the circuit through which current is to be measured.

Conventional direction of the flow of current

. Conventionally, the electric current flow from the positive terminal of the cell to the negative terminal. * But, actually electrons flow from the negative terminal to the positive terminal of the cell.

Mention the smaller units of current

1 milliampere =10^-3 A

. i.e 1 ampere = 1000 mA

1 microampere: = 10^-6 A

i.e 1 ampere =1000000 µA.

Define electric potential difference. (voltage)

Potential difference is defined as the work done to move a unit charge from one point to another in an electric circuit carrying some current.

Define 1 Volt

1 volt is potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to another.

How is pd maintained across the conductor?

. The P.D across the conductor is maintained by connecting its end to the terminals of the cell.

Name the device that is used to measure P.D.? How is it connected in the circuit?

. The device used to measure P.D. is voltmeter. It is connected in parallel to resistor across which potential difference is to be measured.

What do you mean by electric circuit?

The continuous & closed path of an electric current is called electric circuit. If electric circuit is broken from somewhere, current stops flowing through the conductor.

What is circuit diagram?

It is the schematic diagram in which different components of the circuit are represented by the symbols conventionally used.

Mention the factors on which current carrying through a conductor depends

(i) Potential Difference :- Current is directly proportional to the potential difference i.e. if potential difference is doubled the current also gets doubled and if P.D. is halved current also gets halved (ii) Resistance :- Current is inversely proportional to the resistance. i.e if resistance is doubled current gets halved and if resistant is halved current gets doubled.

State ohm’s law

Ohm’s law states that the electric current flowing through a conductor is directly proportional to the potential difference across the ends of the electric conductor, provided that the temperature and other physical conditions of the conductor remain the same.

Define resistance.

Resistance of a conductor is the property of a conductor to oppose the electric charge flowing through it.

What are the factors on which resistance depend?

1. Resistance is directly proportional to the length of the conductor.

2. Resistance is inversely proportional to the area of cross section of the conductor.

3. Resistance of a conductor depends on the nature of the material used in the conductor.

4. If the temperature of a metallic conductor increases, its resistance increases.

5. Resistance is inversely proportional to the square of the diameter.

Define 1 ohm

Resistance of a conductor is said yo be one ohm, if a potential differnce of 1 volt across the ends of a conductor makes an electric current of 1 ampere flow through it.

What is variable resistance?

It is a component which is use to regulate current without changing the voltage source is called variable resistance.

What is a rheostat?

It is a device used in electric circuit to change the resistance in the circuit.

What are conductors?

A component of a given size that offers a low resistance is a good conductor

What is a resistor?

A component having some appreciable resistance is called resistor

What is an insulator?

A component that offers very high resistance is called poor conductor (or insulator)

Why are electrons not completely free to move in a conductor?

Electrons are not completely free to move because their motion is restrained by the attraction of atoms among which they move.

Define resistivity

Resistivity of a conductor is the resitance of a conductor of unit length and unit area of cross section. It is denoted by rho (p).

What are the factors on which resistivity depends for a wire or conductor?

Resistivity of a wire or conductor depends on the nature of the material used for the wire or conductor

Resistivity of a conductor or wire is directly proportional to the change in temperature of the conductor or wire.

Why are alloys like nichrome used in electrical heating devices such as electric toasters, iron, etc.?

Alloys (like nichrome) are used in making electrical heating devices instead of pure metals because (i) Alloys have higher resistivity than pure metals (ii) They do not get oxidized (i.e burn, even at high temperature).

Why are aluminum and copper used for electrical transmission wires?

because they have low resistivities and hence are good conductors of electricity. Also they are cheaper than best conductor silver.

. Why is tungsten used for making filaments of electric bulbs?

because it has very high melting point and when hot emits light.

Mention the features of series combination of resistors

(i) In series circuit net resistance = sum of the resistances of each individual resistor (ii) In series circuit current remains same throughout the circuit.

(iii) In series circuit net potential difference = sum of the potential difference across each resistor.

Mention the features of parallel combination circuit

(i) In parallel circuit reciprocal of net resistance = the sum of the reciprocals of resistances of each individual resistor

(ii) In parallel circuit net current = sum of the current through each resistor

(iii) In parallel circuit potential difference remains same throughout the circuit

DISADVANTAGES OF CONNECTING COMPONENTS IN SERIES CIRCUIT.

(i) Different components require different amount of current to work properly but in series circuit current remains the same through out the circuit

(ii) In series circuit if one component fails then all the components stop working

(iii) There is single switch for all the components

ADVANTAGES OF PARALLEL CIRCUIT

(i) In parallel circuit each component gets same potential difference & current gets divided through each components, due to which they work properly

(ii) In parallel circuit if one component fails all the other components work normally

(iii) There are separate switches for all the components

Why does an electrician spend lot of time in trouble locating the dead bulb of a fairy light.

Because the bulbs in fairy light are connected in series due to which electrician has to check each & every bulb.

What is heating effect of current?

Whenever current is passed through high resistance conductor it becomes very hot due to the production of heat & this is known as heating effect of current.

State joule’s law of heating

According to joules law of heating the heat produced in a resistor is directly proportional to

(i) The square of current for a given resistance

(ii) to the resistance for a given current.

(iii) time for which current flows through the resistor

State the applications of heating effect of current

(i) This effect is utilized in producing heat in electric heating devices such as electric toasters, electric iron, kettle etc. These devices consist of nichrome which become very hot when current is passed through it.

(ii) This effect is all utilized for making filaments of electric bulb to produce light. Filament of bulb is made up of very thin wire of tungsten when current is pass through the filaments it becomes white hot & emits light.

(iii) This effect is also used for making electric fuse a safety device. It consists of a wire of appropriate melting point. If the current exceeds the specified value the wire melts due to the heat produced & breaks the circuit. This prevents the components from any damage & also prevents the accidental fire.

What is electric power?

The rate at which electrical energy is consumed in an electrical circuit is called in electrical power SI unit of power is watt

Define 1 watt

Electric power is said to be one watt when an electric current of one ampere flows through a circuit having potential difference of 1 volt.

Define electrical energy

It is defined as the product of power & time i.e. S I unit of electrical energy is watt-hrs

Define watt hour

1 watt hr is the energy consumed when I watt of power is used for 1 hr * Commercial unit of electrical energy kilowatt hr, commonly called unit

Define kilowatt-hour

A kilowatt hour is defined as the amount of enrgy consumed by an electrical appliance of 100 watts when it operates for an hour.