Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistors and two insulators.
Those substances which have very low electrical resistance are called as good conductors. E.g., copper and aluminium.
Those substances which have comparatively high resistance than conductors are known as resistors. E.g., nichrome and manganin.
Those substances which have infinitely high electrical resistance are called insulators. E.g., rubber and wood.
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 ?
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 ?
A current of 200 mA flows through a 4 kΩ resistor. What is the p.d. across the resistor ?
What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?
Which of the following equation shows the correct relationship between electrical units ?
1 A = 1 C/s or 1 C = 1 A/s
Keeping the resistance constant, the potential difference applied across the ends of a component is halved. By how much does the current change ?
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.
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 ?
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.
What is meant by conductors and insulators ? Give two examples of conductors and two of insulators.
(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).
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 potential difference of 20 volts is applied across the ends of a resistance of 5 ohms. What current will flow in the resistance ?
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 ?
How does the resistance of a wire vary with its :
(a) area of cross-section ?
(b) diameter ?
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 circuit diagram given below shows the combination of three resistors R1 R2 and R3 :
Find : (i) total resistance of the circuit.
(ii) total current flowing in the circuit.
(iii) the potential difference across R1.
Fill in the following blank with a suitable word :
Ohm’s law states a relation between potential difference and……………………
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 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 ?
If five resistances, each of value 0.2 ohm, are connected in series, what will be the resultant resistance ?
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.
Two resistances X and Y are connected turn by turn : (i) in parallel, and (ii) in series. In which case the resultant resistance will be less than either of the individual resistances ?
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
(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 ?
(a) Write down an expression for the resistance of a metallic wire in terms of the resistivity.
What will be the resistance of a metal wire of length 2 metres and area of cross-section 1.55 × 10-6 m2, if the resistivity of the metal be 2.8 × 10-8 Ωm ?
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
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 ?
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 ?
Fill in the following blanks with suitable words :
(a) A current is a flow of……….. For this to happen there must be a………….
(b) Current is measured in……… using an………… placed in……… in a circuit.
(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 ?
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.
