(a) In which direction does conventional current flow around a circuit ?
(b) In which direction do electrons flow ?
(a) Conventional current flows from positive terminal of a battery to the negative terminal, through the outer circuit.
(b) Electrons flow from negative terminal to positive terminal of the battery (opposite to the direction of conventional current).
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 ?
Keeping the resistance constant, the potential difference applied across the ends of a component is halved. By how much does the current change ?
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
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.
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.
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) 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 ?
Name the law which relates the current in a conductor to the potential difference across its ends.
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 ?
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 ?
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) Define the unit of resistance (or Define the unit “ohm”).
What happens to the resistance as the conductor is made thinner ?
Keeping the potential difference constant, the resistance of a circuit is doubled. By how much does the current change ?
What would be the effect on the resistance of a metal wire of :
(a) increasing its length ?
(b) increasing its diameter ?
(c) increasing its temperature ?
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.
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.
What is meant by conductors and insulators ? Give two examples of conductors and two of insulators.
(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 ?
(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 ?
Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistors and two insulators.
(a) What is the ratio of potential difference and current known as ?
(b) The values of potential difference V applied across a resistor and the corresponding values of current I
flowing in the resistor are given below :
(c) Name the law which is illustrated by the above V-I graph.
(d) Write down the formula which states the relation between potential difference, current and resistance,
(e) The potential difference between the terminals of an electric iron is 240 V and the current is 5.0 A. What is the resistance of the electric iron ?
A current of 200 mA flows through a 4 kΩ resistor. What is the p.d. across the resistor ?
If the length of a wire is doubled by taking more of wire, what happens to its resistance ?
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
(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 ?
(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 ?