What is the SI unit of potential difference ?
Volt
(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 should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
What is the general name of the substances having infinitely high electrical resistance ?
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 ?
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 ?
Name the law which relates the current in a conductor to the potential difference across its ends.
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.
(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.
(a) In which direction does conventional current flow around a circuit ?
(b) In which direction do electrons flow ?
Why should the resistance of :
(a) an ammeter be very small ?
(b) a voltmeter be very large ?
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
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 ?
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 ?
A resistance of 20 ohms has a current of 2 amperes flowing in it. What potential difference is there between its ends ?
(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.
If the length of a wire is doubled by taking more of wire, what happens to its resistance ?
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 ?
Show how you would connect two 4 ohm resistors to produce a combined resistance of
(a) 2 ohms
(b) 8 ohms.
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 ?
The atoms of copper contain electrons and the atoms of rubber also contain electrons. Then why does copper conduct electricity but rubber does not conduct electricity ?
(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 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 do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?
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 ?
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.
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.
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……………
