 # Electricity

### Question:

Name the electrical property of a material whose symbol is “omega”.

Resistance.

### Electricity

#### Q 1.

Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?

#### Q 2.

The electrical resistivities of four materials A, B, C and D are given below : Which material is : (a) good conductor (b) resistor (c) insulator, and (d) semiconductor ?

#### Q 3.

If 3 resistances of 3 ohm each are connected in parallel, what will be their total resistance ?

#### Q 4.

What is meant by saying that the electric potential at a point is 1 volt ?

#### Q 5.

What happens to the resistance as the conductor is made thicker ?

#### Q 6.

How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?

#### Q 7.

(a) Name a device that helps to measure the potential difference across a conductor.
(b) How much energy is transferred by a 12 V power supply to each coulomb of charge which it moves around a circuit ?

#### Q 8.

Compare how an ammeter and a voltmeter are connected in a circuit.

#### Q 9.

A p.d. of 10 V is needed to make a current of 0.02 A flow through a wire. What p.d. is needed to make a current of 250 mA flow through the same wire ?

#### Q 10.

How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V ?

#### Q 11.

What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?

#### Q 12.

(a) Name a device which helps to maintain potential difference across a conductor (say, a bulb).
If a potential difference of 10 V causes a current of 2 A to flow for 1 minute, how much energy is
transferred ?

#### Q 13.

A potential difference of 20 volts is applied across the ends of a resistance of 5 ohms. What current will flow in the resistance ?

#### Q 14.

How does the resistance of a conductor depend on :
(a) length of the conductor ?
(b) area of cross-section of the conductor ?
(c) temperature of the conductor ?

#### Q 15.

(a) What do the letters p.d. stand for ?
(b) Which device is used to measure p.d. ?

#### Q 16.

Will current flow more easily through a thick wire or a thin wire of the same material when connected to the same source ? Give reason for your answer.

#### Q 17.

Which of the following statements correctly defines a volt ?
(a) a volt is a joule per ampere.
(b) a volt is a joule per coulomb.

#### Q 18.

What is meant by conductors and insulators ? Give two examples of conductors and two of insulators.

#### Q 19.

Which particles constitute the electric current in a metallic conductor ?

#### Q 20.

What is the unit of electric charge ?

#### Q 21.

If 20 C of charge pass a point in a circuit in 1 s, what current is flowing ?

#### Q 22.

What is nichrome ? State its one use.

#### Q 23.

The atoms of copper contain electrons and the atoms of rubber also contain electrons. Then why does copper conduct electricity but rubber does not conduct electricity ?

#### Q 24.

What actually travels through the wires when you switch on a light ?

#### Q 25.

(a) In which direction does conventional current flow around a circuit ?
(b) In which direction do electrons flow ?

#### Q 26.

The electrical resistivities of three materials P, Q and R are given below : Which material will you use for making (a) electric wires (b) handle for soldering iron, and (c) solar cells ? Give reasons for your choices.

#### Q 27.

A current of 5 amperes flows through a wire whose ends are at a potential difference of 3 volts. Calculate the resistance of the wire.

#### Q 28.

Fill in the following blank with a suitable word :
Ohm’s law states a relation between potential difference and……………………

#### Q 29.

Fill in the following blanks with suitable words :
Resistance is measured in…………….. The resistance of a wire increases as the length…………………. ; as the
temperature………. ; and as the cross-sectional area…………

#### Q 30.

A wire that has resistance R is cut into two equal pieces. The two parts are joined in parallel. What is the resistance of the combination ?

#### Q 31.

What is the SI unit of potential difference ?

#### Q 32.

Why should the resistance of :
(a) an ammeter be very small ?
(b) a voltmeter be very large ?

#### Q 33.

How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?

#### Q 34.

Show how you would connect two 4 ohm resistors to produce a combined resistance of
(a) 2 ohms
(b) 8 ohms.

#### Q 35.

A current of 4 A flows around a circuit for 10 s. How much charge flows past a point in the circuit in this time ?

#### Q 36.

Name the law which relates the current in a conductor to the potential difference across its ends.

#### Q 37.

Keeping the resistance constant, the potential difference applied across the ends of a component is halved. By how much does the current change ?

#### Q 38.

Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?

#### Q 39.

Name the material which is used for making the heating element of an electric iron.

#### Q 40.

What would be the effect on the resistance of a metal wire of :
(a) increasing its length ?
(b) increasing its diameter ?
(c) increasing its temperature ?

#### Q 41.

Which of the two is connected in series : ammeter or voltmeter ?

#### Q 42.

(a) Define the unit of resistance (or Define the unit “ohm”).
What happens to the resistance as the conductor is made thinner ?
Keeping the potential difference constant, the resistance of a circuit is doubled. By how much does the current change ?

#### Q 43.

Name the unit of electrical resistance and give its symbol.

#### Q 44.

What is Ohm’s law ? Explain how it is used to define the unit of resistance.

#### Q 45.

On what factors does the resistance of a conductor depend ?

#### Q 46.

Give the law of combination of resistances in series.

#### Q 47.

What is the current in a circuit if the charge passing each point is 20 C in 40 s ?

#### Q 48.

What is an ammeter ? How is it connected in a circuit ? Draw a diagram to illustrate your answer.

#### Q 49.

An electric heater is connected to the 230 V mains supply. A current of 8 A flows through the heater.
(a) How much charge flows around the circuit each second ?
(b) How much energy is transferred to the heater each second ?

#### Q 50.

State the factors on which the strength of electric current flowing in a given conductor depends.