Calculate the combined resistance in each case :
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 ?
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 ?
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
(a) How many milliamperes are there in 1 ampere ?
(b) How many microamperes are there in 1 ampere ?
(a) In which direction does conventional current flow around a circuit ?
(b) In which direction do electrons flow ?
In 10 s, a charge of 25 C leaves a battery, and 200 j of energy are delivered to an outside circuit as a result.
(a) What is the p.d. across the battery ?
(b) What current flows from the battery ?
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.
(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.
Show how you would connect two 4 ohm resistors to produce a combined resistance of
(a) 2 ohms
(b) 8 ohms.
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.
What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?
(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 ?
Name the law which relates the current in a conductor to the potential difference across its ends.
A resistance of 20 ohms has a current of 2 amperes flowing in it. What potential difference is there between its ends ?
A p.d. of 10 V is needed to make a current of 0.02 A flow through a wire. What p.d. is needed to make a current of 250 mA flow through the same wire ?
Why should the resistance of :
(a) an ammeter be very small ?
(b) a voltmeter be very large ?
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 ?
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.
How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?
What is the general name of the substances having infinitely high electrical resistance ?
Keeping the resistance constant, the potential difference applied across the ends of a component 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.
(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.
(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) 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 ?
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) 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 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 ?
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 ?
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 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.
The electrical resistivities of five substances A, B, C, D and E are given below :
A 5.20 x l0-8 Ω m
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.
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 ?
