(a) State the relation between potential difference, work done and charge moved.
(b) Calculate the work done in moving a charge of 4 coulombs from a point at 220 volts to another point at 230 volts.
(a) Potential difference = Work done/Charge moved.
(b) V1=220 V, V2=230V, Charge moved=4C
Thus, the potential difference= V2- V1 =230-220
=10.
We know that,
Work done = Potential difference x Charge moved
= 10 x 4
Work done = 40 joules
(a) How many milliamperes are there in 1 ampere ?
(b) How many microamperes are there in 1 ampere ?
How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
Name the law which relates the current in a conductor to the potential difference across its ends.
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
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.
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 ?
What is the general name of the substances having infinitely high electrical resistance ?
Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistors and two insulators.
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
Three resistors are connected as shown in the diagram.
Through the resistor 5 ohm, a current of 1 ampere is flowing,
(i) What is the current through the other two resistors ?
(ii) What is the p.d. across AB and across AC ?
(iii) What is the total resistance ?
For the circuit shown in the diagram below :
What is the value of :
(i) current through 6 Ωresistor ?
(ii) potential difference across 12 Ω resistor ?
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 ?
How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?
What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?
The p.d. across a lamp is 12 V. How many joules of electrical energy are changed into heat and light when :
(a) a charge of 1 C passes through it ?
(b) a charge of 5 C passes through it ?
(c) a current of 2 A flows through it for 10 s ?
A piece of wire of resistance 20 Ω is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.
Show how you would connect two 4 ohm resistors to produce a combined resistance of
(a) 2 ohms
(b) 8 ohms.
Two resistors, with resistances 5 Ω and 10 Ω respectively are to be connected to a battery of emf 6 V so as to obtain :
(i) minimum current flowing (ii) maximum current flowing
(a) How will you connect the resistances in each case ? .
(b) Calculate the strength of the total current in the circuit in the two cases.
How much work is done when one coulomb charge moves against a potential difference of 1 volt ?
(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 ?
Which of the following equation shows the correct relationship between electrical units ?
1 A = 1 C/s or 1 C = 1 A/s
Why should the resistance of :
(a) an ammeter be very small ?
(b) a voltmeter be very large ?
Keeping the resistance constant, the potential difference applied across the ends of a component is halved. By how much does the current change ?
(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 ?
(a) What is the ratio of potential difference and current known as ?
(b) The values of potential difference V applied across a resistor and the corresponding values of current I
flowing in the resistor are given below :
(c) Name the law which is illustrated by the above V-I graph.
(d) Write down the formula which states the relation between potential difference, current and resistance,
(e) The potential difference between the terminals of an electric iron is 240 V and the current is 5.0 A. What is the resistance of the electric iron ?
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 ?
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 ?
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
(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 × 10-8 Ωm.
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 ?
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 ?
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……………
(a) What do you understand by the term “potential difference” ?
(b) What is meant by saying that the potential difference between two points is 1 volt ?
(c) What is the potential difference between the terminals of a battery if 250 joules of work is required to transfer 20 coulombs of charge from one terminal of battery to the other ?
(d) What is a voltmeter ? How is a voltmeter connected in the circuit to measure the potential difference between two points. Explain with the help of a diagram.
(e) State whether a voltmeter has a high resistance or a low resistance. Give reason for your answer.
