Electricity

Question:

Draw circuit symbols for (a) fixed resistance (b) variable resistance (c) a cell (d) a battery of three cells (e) an open switch (f) a closed switch.

Electricity

Q 1.

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

Q 2.

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

Q 3.

What is the unit of electric charge ?

Q 4.

How does the resistance of a wire change when :
(i) its length is tripled ?
(ii) its diameter is tripled ?
(in) its material is changed to one whose resistivity is three times ?

Q 5.

Which among iron and mercury is a better conductor of electricity ?

Q 6.

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 7.

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

Q 8.

A current of 200 mA flows through a 4 kÎ© resistor. What is the p.d. across the resistor ?

Q 9.

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 10.

(a) Give two examples of substances which are good conductors of electricity. Why do you think they are
good conductors of electricity ?
Calculate the resistance of a copper wire 1.0 km long and 0.50 mm diameter if the resistivity of copper is 1.7 Ã— 10-8 Î©m.

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.

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

Q 13.

The circuit diagram given below shows the combination of three resistors R1 R2 and R3 :

Find : (i) total resistance of the circuit.
(ii) total current flowing in the circuit.
(iii) the potential difference across R1.

Q 14.

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

Q 15.

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

Q 16.

Which of the following equation shows the correct relationship between electrical units ?
1 A = 1 C/s or 1 C = 1 A/s

Q 17.

(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 18.

Name the material which is the best conductor of electricity.

Q 19.

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 20.

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 21.

If five resistances, each of value 0.2 ohm, are connected in series, what will be the resultant resistance ?

Q 22.

An electric bulb of resistance 20 Î© and a resistance wire of 4 Î© are connected in series with a 6 V battery. Draw the circuit diagram and calculate :
(a) total resistance of the circuit.
(b) current through the circuit.
(c) potential difference across the electric bulb.
(d) potential difference across the resistance wire.

Q 23.

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 24.

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

Q 25.

What do the following symbols mean in circuit diagrams ?

Q 26.

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 27.

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

Q 28.

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 29.

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 30.

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 31.

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 32.

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

Q 33.

The graph between V and 1 for a conductor is a straight line passing through the origin.
Which law is illustrated by such a graph ?
What should remain constant in a statement of this law ?

Q 34.

Find the current in each resistor in the circuit shown below :

Q 35.

By what name is the physical quantity coulomb/second called ?

Q 36.

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

Q 37.

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

Q 38.

What is the SI unit of potential difference ?

Q 39.

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

Q 40.

On what factors does the resistance of a conductor depend ?

Q 41.

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

Q 42.

What is nichrome ? State its one use.

Q 43.

(a) Write down an expression for the resistance of a metallic wire in terms of the resistivity.
What will be the resistance of a metal wire of length 2 metres and area of cross-section 1.55 Ã— 10-6 m2, if the resistivity of the metal be 2.8 Ã— 10-8 Î©m ?

Q 44.

Two resistances X and Y are connected turn by turn : (i) in parallel, and (ii) in series. In which case the resultant resistance will be less than either of the individual resistances ?

Q 45.

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 46.

Define one coulomb charge.

Q 47.

(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 48.

What is the flow of charge called ?

Q 49.

(a) How many milliamperes are there in 1 ampere ?
(b) How many microamperes are there in 1 ampere ?

Q 50.

Draw a circuit diagram to show how 3 bulbs can be lit from a battery so that 2 bulbs are controlled by the same switch while the third bulb has its own switch.