 # Electricity

### Question:

Three 2 V cells are connected in series and used as a battery in a circuit.
(a) What is the p.d. at the terminals of the battery ?
(b) How many joules of electrical energy does 1 C gain on passing through (i) one cell (ii) all three cells ?

(a) If three cells of 2 volt each are connected in series to make a battery, then the total potential difference between terminals of the battery will be 6V.
(b) (i) Given: p.d. = 2V, Charge moved = 1C
We know that
Work done = p.d. x charge moved
= 2 x 1
Work done = 2 joules
(ii) Given: p.d. = 6V, Charge moved = 1C
Work done = p.d. x charge moved
= 6 x1
Work done = 6 joule.

### Electricity

#### Q 1.

What is the unit of electric current ?

#### Q 2.

What do the following symbols mean in circuit diagrams ? #### Q 3.

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

#### Q 4.

(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 5.

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

#### Q 6.

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

#### Q 7.

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 8.

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

#### Q 9.

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

#### Q 10.

Name the material which is the best conductor of electricity.

#### Q 11.

What is nichrome ? State its one use.

#### Q 12.

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 13.

Give the law of combination of resistances in series.

#### Q 14.

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

#### Q 15.

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

#### Q 16.

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 17.

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 18.

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

#### Q 19.

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 20.

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

#### Q 21.

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

#### Q 22.

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

#### Q 23.

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

#### Q 24.

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

#### Q 25.

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

#### Q 26.

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 27.

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

#### Q 28.

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 29.

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

#### Q 30.

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

#### Q 31.

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

#### Q 32.

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

#### Q 33.

Calculate the combined resistance in each case : #### Q 34.

A battery of 9 V is connected in series with resistors of 0.2 Î©, 0.3 Î©, 0.4 Î©, 0.5 Î© and 12 Î©. How much current would flow through the 12 Î© resistor ?

#### Q 35.

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 ?

#### Q 36.

What is the SI unit of potential difference ?

#### Q 37.

Which particles constitute the electric current in a metallic conductor ?

#### Q 38.

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

#### 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.

Name the unit of electrical resistance and give its symbol.

#### Q 41.

Name the physical quantity whose unit is “ohm”.

#### 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.

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 44.

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

#### Q 45.

(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 46.

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

#### Q 47.

What is the unit of electric charge ?

#### Q 48.

(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 49.

(a) What is an electric current ? What makes an electric current flow in a wire ?
(b) Define the unit of electric current (or Define ampere).

#### Q 50.

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