What is the unit of electric charge ?
Coulomb
Name the law which relates the current in a conductor to the potential difference across its ends.
(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 ?
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
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 ?
What is the general name of the substances having infinitely high electrical resistance ?
(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.
Calculate the area of cross-section of a wire if its length is 1.0 m, its resistance is 23 Ω and the resistivity of the material of the wire is 1.84 x 10-6 Ωm.
If 3 resistances of 3 ohm each are connected in parallel, what will be their total resistance ?
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 resistance of 20 ohms has a current of 2 amperes flowing in it. What potential difference is there between its ends ?
Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistors and two insulators.
(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.
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
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.
(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).
If the charge on an electron is 1.6 x 10-19 coulombs, how many electrons should pass through a conductor in 1 second to constitute 1 ampere current ?
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.
How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?
(a) In which direction does conventional current flow around a circuit ?
(b) In which direction do electrons flow ?
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 ?
(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.
The electrical resistivities of five substances A, B, C, D and E are given below :
A 5.20 x l0-8 Ω m
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
Show how you would connect two 4 ohm resistors to produce a combined resistance of
(a) 2 ohms
(b) 8 ohms.
Which has less electrical resistance : a thin wire or a thick wire (of the same length and same material) ?
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.
What possible values of resultant resistance one can get by combining two resistances, one of value 2 ohm and the other 6 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 ?
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 ?
