Question Pool Current Electricity

Current Electricity - SAMAGRA Question Pool & Answers | Class 12

Kerala Syllabus SAMAGRA SCERT SAMAGRA Question Pool for Class 12 Physics Current Electricity

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Qn 1.

The variation of resistivity (ρ) with temperature (T) of a conductor, semiconductor and super conductor are given in the figure.

 


a)Identify them from the graph.

b)Identify the figure in which the temperature coefficient of resistance of the material is
positive.

c)Write the equation connecting resistivity of the material with relaxation time.



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Qn 2.

The resistance value of a conductor depends on its physical dimensions.

a) Give the expression for resistance of a conductor in terms of its physical dimension.

b)

                             (l length and d diameter)

A potential V is applied between the ends of two conductor of same material shown in the figure.
i) Express the resistance of the second conductor in terms of the resistance of the first conductor.
ii) Find the ratio of electric field across the two conductors.



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Qn 3.

Explain the principle of a potentiometer. How can emf of two cells be compared using potentiometer?



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Qn 4.

If the length of a copper wire has a certain resistance R, then on doubling the length its specific resistance

(a) will be doubled

(b) will become 1/4th

(c) will become 4 times

(d) will remain the same.



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Qn 5.

The variation of potential difference F with length l in case of two potentiometer X and Y is as shown in fig.

                                   

Which one of these two will you prefer for comparing emfs of two cells and why?



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Qn 6.

Of which material is a potentiometer wire normally made?


 



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Qn 7.

on what factors does the internal resistance of a cell depend?



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Qn 8.
The potential difference across a given copper wire is increased. What happen to the drift

velocity of the charge carries.

 



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Qn 9.

Define electromotive force (emf) of a cell



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Qn 10.

The voltage current variation of two metallic wires X and Y at constant temperature are as shown in fig.

                                                   

Assuming that the wires have the same length and die same diameter, explain which

wire will have a larger resistivity and why?



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Qn 11.

A given wire having resistance R is stretched so as to reduce its diameter to half of its previous value. What will be its new resistance?


 



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Qn 12.

Two wires of equal lengths, one of copper and the other of manganin have the same resis­tance.

Which wire is thicker?



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Qn 13.

A wire of resistance one ohm is stretched to double its length what is the new resistance?

 



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Qn 14.

A wire has a resistance of 90Ω and it is cut into three pieces having equal lengths.

If these wire now connected in parallel/find the resistance of the combination so formed.



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Qn 15.

What is a non-ohmic device? Give one example.



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Qn 16.

The potential difference across a given copper wire is increased. .What happens to the drift velocity of the charge carriers?



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Qn 17.

While performing experiments with potentiometer (or metre bridge) the jockey should not be

rubbed against the wire" Why?



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Qn 18.

While performing an experiment with potentiometer the deflection in the galvanom­eter is found to be

in the same direction, both at the starting end and the extreme end of the wire. Also it is seen that

(i) the deflection is less at the other extreme end than at the start end and

(ii) the deflection is more at the extreme end than at the starting end. Why?



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Qn 19.

What do you mean by potential gradient of a potentiometer?



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Qn 20.

The potentiometer wire must be long and of uniform thickness" Why?



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Qn 21.

Which is preferred for measuring e.m.f. of a cell, a voltmeter or a potentiometer" Why?



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Qn 22.

Why a potentiometer is called so?



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Qn 23.

"Wheatstone bridge method of determination of resistance is considered to be more accurate than the voltmeter-ammeter method" Why?



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Qn 24.

"Kirchhoff's laws are related to certain conservation laws" Name them.



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Qn 25.

Two wires of equal lengths, one of copper and the other or manganin, have the same resistance.

Which wire is thicker?



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Qn 26.

It is easier to start a car engine on a warm day than on a chilly day. Why?



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Qn 27.

steady current flows in a metallic conductor of non-uniform cross-section. Say which of these quantities is constant along the conductor :

current, current density, electric field, drift speeds



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Qn 28.

Name the carriers of electric current in

a) bar made of silver. b) hydrogen discharge tube.c) voltaic cell.

d) lead accumulator being charged by an external supply.

e) germanium semiconductor.

f) a wire made of the alloy nichrome. g) a superconductor.



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Qn 29.

Are the paths of electrons straight lines between successive collisions with the positive ions of the metal in the

(i) absence of electric field,

(ii) presence of electric field?



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Qn 30.

When electrons drift in a metal from a lower to a higher potential, does it mean that all the free electrons of the metal are moving in the same direction?



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Qn 31.

The electron drift speed is estimated to be only a few mm/s for currents in the range of a few A. How then is current established almost the instant, a circuit is closed?



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Qn 32.

In a resistance box there is a resistance marked infinity. What is the length of the wire used for making this infinite resistance?



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Qn 33.

Why manganin is preferred for making standard resistance?



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Qn 34.

A metal contains a large number of free electrons and they are in motion. Then why there is no current in a piece of wire which it is not connected to a cell?



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Qn 35.

What is the charge on a wire, when a current flow through the wire?



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Qn 36.

a) State whether the following statement is correct.
‘‘If the current through the cell is from its positive to negative, against the direction of
emf, then the potential drop across the internal resistance aids the emf of the cell.’’
b) You are given two cells. Group them so that they give more voltage. Arrive at the expression for effective emf and internal resistance.



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Qn 37.

a) Kirchhoff’s second law is a consequence of
              i) Law of conservation of angular momentum

               ii) Law of conservation of energy

              iii)Law of conservation of charge iv) None of these.
b) Find the potential difference across the resistance 2Ω in the given network.

                             

 



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Qn 38.

The Figure shows the arrangement of five identical bulbsR1 ,R2 ,R3 ,R4 and R5

                                                                          

a) When the switch is closed will all the bulbs glow? Give reason.
b) Identify the underlying principle. Deduce the principle for a resistance network.



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Qn 39.

The Figure shows the diagram of a potentiometer.

                                                           

a) Give the principle of a potentiometer.
b) The length of AB is 3m and resistance per unit length of the potentiometer wire is 4Ω/m. If E 1 = 4V, R=20Ω

and E 2 =1 V find the length of the potentiometer wire that balances E 2 .
c) If E 2 > E 1 can we get the null deflection in galvanometer. Give reason



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Qn 40.

The figure shows the V-I characteristics of two resistors R 1 , R 2 and the effective resistance of
the series and parallel combinations. (R1 >R 2 ).
a) Identify from the graph whether these resistors are ohmic or non-ohmic?
b) Match the graphs with the corresponding resistances.



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Qn 41.

a)Define electric power. What is its SI Unit?
b) Two bulbs of 50W, 220V and 100W, 220Vare given. How will you connect the bulbs so that50W, 220V bulb will glow brighter than 100W, 220V bulb.
c) When the bulb 50W, 220V is connected to an 110V supply calculate the power generated.



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Qn 42.

A student was asked to compare the resistance of two conductors using a meter bridge apparatus.
a) What is the working principle of Meter Bridge.
b) Draw the necessary circuit diagram for the experiment.
c) Write an expression for the ratio of resistances.
d)A Meter bridge wire has resistance0.2 Ω /cm. The bridge is balanced at 60cm from the
end of an unknown resistance X. If the known resistance is 2 Ω , find the current
flowing through the circuit in the balanced condition if a cell of 8V is connected in the
circuit.



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Qn 43.

When potential difference is applied between the ends of conductor the electrons will flow through the conductor with a constant average velocity.
a) Name the velocity
b) A potential ‘V’is applied across a conductor of length ‘l’. Keeping the potential difference same, the length of the conductor is halved. How does the velocity of electrons change?
c) Write the colour code of the resistor of resistance (540±10%) MΩ



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Qn 44.

An electric circuit is given in the Figure

The potential difference between A and D is 40V.
a) Find the effective resistance between A and D in terms of R.
b) Calculate the potential difference between A and E.



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Qn 45.

Three resistors R 1 ,R 2 ,R 3 are to be combined as shown in the figure.

Fig (i)

Fig(ii)

a)Identify the series and parallel combinations.

b)Which combination has lowest resistance. Arrive at the expression for the effective resistance of this.
 



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Qn 46.

The temperature coefficient of resistance of tungsten is 0.0045/ °C.The resistance of a tungsten coil at 30°C is 45 Ω. What will be its resistance at 70°C



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Qn 47.

Calculate the relaxation time in a metallic conductor from the following data.Conduction electrons

per m3 =5.8x1028, mass of electron 9.1 x 10-31 Kg. Resistivity = 1.6 x 10-8 Ωm



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Qn 48.

An electron of charge e is revolving around a nucleus with speed v in a circular orbit of radius r.

Calculate the equivalent current



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Qn 49.

Through a conductor 10 electrons flow per second. Estimate the current.



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