# Electricity

### Question:

Which particles constitute the electric current in a metallic conductor ?

Electrons.

### Electricity

#### Q 1.

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

#### Q 2.

What is the SI unit of potential difference ?

#### Q 3.

Fill in the following blanks with suitable words :
(a) Potential difference is measured in………….. by using a……………. placed in………… across a component.
(b) Copper is a good………….. Plastic is an……………

#### Q 4.

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

#### Q 5.

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

#### Q 6.

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

#### Q 7.

How much work is done when one coulomb charge moves against a potential difference of 1 volt ?

#### Q 8.

What is the unit of electric current ?

#### Q 9.

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

#### Q 10.

Name the unit of electrical resistance and give its symbol.

#### Q 11.

Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistors and two insulators.

#### Q 12.

Why are copper and aluminium wires usually used for electricity transmission ?

#### Q 13.

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 14.

A piece of wire of resistance 20 Î© is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.

#### Q 15.

How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?

#### Q 16.

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

#### Q 17.

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

#### Q 18.

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

#### Q 19.

What do the following symbols mean in circuit diagrams ?

#### Q 20.

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 21.

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

#### Q 22.

Fill in the following blanks with suitable words :
(a) A current is a flow of……….. For this to happen there must be a………….
(b) Current is measured in……… using an………… placed in……… in a circuit.

#### Q 23.

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 24.

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

#### Q 25.

If the length of a wire is doubled by taking more of wire, what happens to its resistance ?

#### Q 26.

Name the material which is the best conductor of electricity.

#### Q 27.

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

#### Q 28.

What is nichrome ? State its one use.

#### Q 29.

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

#### Q 30.

(a) Give one example to show how the resistance depends on the nature of material of the conductor.
(b) Calculate the resistance of an aluminium cable of length 10 km and diameter 2.0 mm if the resistivity of aluminium is 2.7 x 10-8Î©m.

#### Q 31.

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 32.

(a) Define resistivity. Write an expression for the resistivity of a substance. Give the meaning of each symbol
which occurs in it.
(b) State the SI unit of resistivity.
(c) Distinguish between resistance and resistivity.
(d) Name two factors on which the resistivity of a substance depends and two factors on which it does not depend.
(e) The resistance of a metal wire of length 1 m is 26 Î© at 20 °C. If the diameter of the wire is 0.3 mm, what will be the resistivity of the metal at that temperature ?

#### Q 33.

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

#### Q 34.

What is the SI unit of potential difference ?

#### Q 35.

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

#### Q 36.

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

#### Q 37.

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

#### Q 38.

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

#### Q 39.

In 10 s, a charge of 25 C leaves a battery, and 200 j of energy are delivered to an outside circuit as a result.
(a) What is the p.d. across the battery ?
(b) What current flows from the battery ?

#### Q 40.

A student made an electric circuit shown here to measure the current through two lamps.
(a) Are the lamps in series or parallel ?
(b) The student has made a mistake in this circuit.
What is the mistake ?
(c) Draw a circuit diagram to show the correct way to connect the circuit.
Use the proper circuit symbols in your diagram.

#### Q 41.

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

#### Q 42.

Name the physical quantity whose unit is “ohm”.

#### Q 43.

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

#### Q 44.

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 45.

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

#### Q 46.

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 47.

Give the law of combination of resistances in series.

#### Q 48.

What possible values of resultant resistance one can get by combining two resistances, one of value 2 ohm and the other 6 ohm ?

#### Q 49.

Calculate the combined resistance in each case :

#### Q 50.

For the circuit shown in the diagram below :

What is the value of :
(i) current through 6 Î©resistor ?
(ii) potential difference across 12 Î© resistor ?