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

Resistance.

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

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 ?

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

How does the resistance of a wire vary with its :

(a) area of cross-section ?

(b) diameter ?

(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 ?

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 ?

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

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

(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 ?

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

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 ?

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.

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.

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

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 ?

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

(b) In which direction do electrons flow ?

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.

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.

Fill in the following blank with a suitable word :

Ohm’s law states a relation between potential difference and……………………

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…………

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 ?

Why should the resistance of :

(a) an ammeter be very small ?

(b) a voltmeter be very large ?

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

Show how you would connect two 4 ohm resistors to produce a combined resistance of

(a) 2 ohms

(b) 8 ohms.

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 ?

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

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

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

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 ?

(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 ?

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

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 ?

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