(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.
(a) Potential difference between two points in an electric circuit is defined as the amount of work done in moving a unit charge from one
point to the other point.
(b) The potential difference between two points is 1 volt means 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other.
(c) Given: Work done = 250J, Charge moved = 20C.
we know that,Potential difference = Work done/Charge moved
=250/20=12.5
(d) A voltmeter is a device which is used to measure the potential difference between two points in an electric circuit. Voltmeter is always connected in parallel across the two points where the potential difference is to be measured.
(e) Voltmeter has a high resistance so that it takes a negligible current from the circuit.
(a) How many milliamperes are there in 1 ampere ?
(b) How many microamperes are there in 1 ampere ?
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?
Name the law which relates the current in a conductor to the potential difference across its ends.
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
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 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 ?
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.
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
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 ?
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 ?
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 ?
An electric bulb of resistance 20 Ω and a resistance wire of 4 Ω 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.
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 ?
How much work is done when one coulomb charge moves against a potential difference of 1 volt ?
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……………
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 ?
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.
(a) What is meant by the “resistance of a conductor” ? Write the relation between resistance, potential
difference and current.
(b) When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Calculate the value of the resistance of the resistor.
(a) Why do electricians wear rubber hand gloves while working with electricity ?
(b) What p.d. is needed to send a current of 6 A through an electrical appliance having a resistance of 40 Ω ?
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 current of 200 mA flows through a 4 kΩ resistor. What is the p.d. across the resistor ?
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.
(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 10-8Ωm.
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 in moving a charge of 2 C across two points having a potential difference of 12 V ?
(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 ?
