What is the general name of the substances having infinitely high electrical resistance ?
Insulators.
What is an ammeter ? How is it connected in a circuit ? Draw a diagram to illustrate your answer.
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 ?
What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?
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 ?
Keeping the resistance constant, the potential difference applied across the ends of a component is halved. By how much does the current change ?
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.
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 ?
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…………
(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) What is an electric current ? What makes an electric current flow in a wire ?
(b) Define the unit of electric current (or Define ampere).
A potential difference of 20 volts is applied across the ends of a resistance of 5 ohms. What current will flow in the resistance ?
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 ?
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.
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 ?
What is meant by conductors and insulators ? Give two examples of conductors and two of insulators.
Which of the following equation shows the correct relationship between electrical units ?
1 A = 1 C/s or 1 C = 1 A/s
Fill in the following blank with a suitable word :
Ohm’s law states a relation between potential difference and……………………
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.
A current of 200 mA flows through a 4 kΩ resistor. What is the p.d. across the resistor ?
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?
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.
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.
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) Name a device which helps to maintain potential difference across a conductor (say, a bulb).
If a potential difference of 10 V causes a current of 2 A to flow for 1 minute, how much energy is
transferred ?
Why should the resistance of :
(a) an ammeter be very small ?
(b) a voltmeter be very large ?
How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?
State the factors on which the strength of electric current flowing in a given conductor depends.
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
(a) How does the resistance of a pure metal change if its temperature decreases ?
(b) How does the presence of impurities in a metal affect 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.
(a) Define resistivity. Write an expression for the resistivity of a substance. Give the meaning of each symbol
which occurs in it.
(b) State the SI unit of resistivity.
(c) Distinguish between resistance and resistivity.
(d) Name two factors on which the resistivity of a substance depends and two factors on which it does not depend.
(e) The resistance of a metal wire of length 1 m is 26 Ω at 20 °C. If the diameter of the wire is 0.3 mm, what will be the resistivity of the metal at that temperature ?
The electrical resistivities of five substances A, B, C, D and E are given below :
A 5.20 x l0-8 Ω m
If five resistances, each of value 0.2 ohm, are connected in series, what will be the resultant resistance ?
