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.
Given: Two resistors with resistances R1=5ohm and R2=10ohm, V=6volt
(a) For minimum current these two should be connected in series. For maximum current these two should be connected in parallel.
(b)In series,
Total resistance = 5+10 = 15ohms
Therefore total current drawn = V/R = 6/15 = 0.4amps
In parallel,
Total resistance R is given as
1/R=1/R1+1/R2
1/R=1/5+1/10
1/R=3/10
R=10/3ohm
Therefore total current drawn by the circuit = V/R = 6/(10/3) =1.8amps.
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
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 ?
How should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
(a) How many milliamperes are there in 1 ampere ?
(b) How many microamperes are there in 1 ampere ?
Name the law which relates the current in a conductor to the potential difference across its ends.
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) What is an electric current ? What makes an electric current flow in a wire ?
(b) Define the unit of electric current (or Define ampere).
Keeping the potential difference constant, the resistance of a circuit is halved. By how much does the current change ?
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal ?
(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 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 battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω. How much current would flow through the 12 Ω resistor ?
(a) What do you understand by the term “potential difference” ?
(b) What is meant by saying that the potential difference between two points is 1 volt ?
(c) What is the potential difference between the terminals of a battery if 250 joules of work is required to transfer 20 coulombs of charge from one terminal of battery to the other ?
(d) What is a voltmeter ? How is a voltmeter connected in the circuit to measure the potential difference between two points. Explain with the help of a diagram.
(e) State whether a voltmeter has a high resistance or a low resistance. Give reason for your answer.
Why should the resistance of :
(a) an ammeter be very small ?
(b) a voltmeter be very large ?
(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 should the two resistances of 2 ohms each be connencted so as to produce an equivalent resistance of 1 ohm ?
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 ?
State the factors on which the strength of electric current flowing in a given conductor depends.
Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistors and two insulators.
(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 ?
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 ?
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 ?
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 ?
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.
How many electrons are flowing per second past a point in a circuit in which there is a current of 5 amp ?
Fill in the following blank with a suitable word :
Ohm’s law states a relation between potential difference and……………………
If the length of a wire is doubled by taking more of wire, what happens to its 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.
Which of the following resistor arrangement, A or B, has the lower combined resistance ?
How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V ?
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……………
What is meant by conductors and insulators ? Give two examples of conductors and two of insulators.
