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Current Electricity
Unit II: Current Electricity
Electric current, flow of electric charges in a metallic conductor, drift velocity, mobility and their relation
with electric current; Ohm’s law, electrical resistance, V-I characteristics (linear and non-linear), electrical
energy and power, electrical resistivity and conductivity. Carbon resistors, colour code for carbon resistors;
series and parallel combinations of resistors; temperature dependence of resistance.
Internal resistance of a cell, potential difference and emf of a cell, combination of cells in series and in
parallel.
Kirchhoff’s laws and simple applications. Wheatstone bridge, metre bridge.
Potentiometer - principle and its applications to measure potential difference and for comparing emf of two
cells; measurement of internal resistance of a cell.
[1993]
Q.1
In the circuit in fig, the current in 4 resistance is 1.2 A, what is the potential difference between B
and C.
4
I1
A

I2
I
8

B
2

C
[1994]
Q.1
Deduce ohm’s law using the concept of drift velocity.
[1995]
Q.1
Manganin is used for making standard resistors, why?
[1996]
Q.1
Q.2
Q.3
Q.4
Name the device used for measuring the internal resistance of a secondary cell.
If the temperature of the cold junction of a thermocouple is lowered, what will be the effect on its
neutral temperature?
State Kirchhoff’s laws for electrical circuits.
State Faraday’s laws of electrolysis.
[1997]
Q.1
A potentiometer wire AB, shown in fig is 4m long. Where should the free end of the galvanometer be
connected to AB, so that the galvanometer shows zero deflection?
12
8
A
zz
z
CBSE TWENTY TWO YEAR PAPERS
G
B
P
zz
z
zz
z
(1)
AURORA CLASSES
[1998]
Q.1
Q.2
Q.3
Draw the graph showing the variation of Seebeck coefficient with temperature of hot junction.
Why do we prefer a potentiometer to measure emf of a cell rather than a voltmeter?
Rh
The following circuit shows the use of
Drive cell
potentiometer to measure the internal
4V
resistance of a cell
(i)
When the key K is open, how does
the balance point change, if the
A
current form the driver cell
B
decreases.
G
(ii)
When the key K is closed, how
does the balance point change if R
is increased keeping current from
1.5V
the driver cell constant?


K
R
Q.4
Q.5
Q.6
Two electric bulbs on inversion temperature if the temperature of cold junction increases?
Explain with the help of a circuit diagram how the value of unknown resistance can be determined
using a Wheatstone’s Bridge. Give the formula used.
A voltmeter V of resistance 400  is used to measure the potential difference across a 100  resistor
in the circuit shown here
(a)
What will be the reading of the voltmeter?
(b)
Calculate the potential difference across 100  resistors before the voltmeter is connected.
84V
R1 = 100 
 
V
R2 = 200 
 
[1999]
RV
Q.1
Q.2
Q.3
Q.4
Q.5
Q.6
How does the resistance of a ohmic depend upon the applied voltage?
What is the effect of temperature on relaxation time of electrons in metal?
How does the electrical conductivity of an electrolyte change with decrease of temperature?
The applied p.d. across a given resistance is altered so that heat produced per second increased by a
factor of 16. By what factor does the applied p.d. change?
Two heating coils one of fine wire and other of thick wire made of same material and of same length
is connected one by one to a source of electricity. Which one coil will produce heat at greater rate.
In the circuit diagram given below AB is a uniform wire of
R
E1
resistance 10  and length 1m. It is connected to a series
arrangement of cell E, of emf 2.0 V and negligible internal
resistance and resistor R Terminal A is also connected to an
J
B
electrochemical cell E2 of emf 100 mV and a galvanometer A
G. In this set up a balancing point is obtained at 40 cm mark
from A. Calculate the value of resistance R. If R2 were to
G
have an emf of 300 mV, where will you expect the balancing
E2
point to be.
CBSE TWENTY TWO YEAR PAPERS
(2)
AURORA CLASSES
[2000]
Q.1
Name the liquid which is a good conductor of electricity but does not undergo electrolysis on passage
electric current?
Q.2
Two electric bulbs whose resistances are in the ratio 1 : 2 are connected in parallel to a source of
constant voltage. What will be the ratio of power dissipation in these wires?
Q.3
A toaster produces more heat than a light bulb when connected in parallel to a 220 V mains. Which of
the two has greater resistance?
[2001]
Q.1
Find the current drawn from a cell of emf 1 V and internal resistance 2/3 connected to the network
given adjoint.
1
B
A
.
1
P
1
1
1
.
C
D
1
2/3
1V
Q.2
Q
Fig. Shows mass deposited versus time graph of a voltmeter for two current i 1 and i2. Which current is
more?
t1
m
t2
t
Q.3
Define relaxation time of electrons in a conductor. Explain how it varies with increases of
temperature. State the relation between resistivity and relaxation time.
Q.4
In a practical Wheatsone’s bridge circuit, wire AB is 2m long. When resistance Y = 2.0  and jockey
is in position J such that AJ = 1.20 m, there is no current in galvanometer, find the value of unknown
resistance X. The resistance per unit length of wire AB = 0.01 /cm. Also calculate the current drawn
by the cell of emf 4.0 V and negligible internal resistance.
Y=2
X
.
D

A
.
P

Q
.
B
J
G

E = 4.0 V
CBSE TWENTY TWO YEAR PAPERS
(3)
AURORA CLASSES
[2002]
Q.1
Q.2
Q.3
Q.4
Q.5
Q.6
Q.7
Q.8
Which physical quantity does the voltage versus current graph for a metallic conductor dipict? Give
its S.I. Units.
How does the drift velocity of electrons in a metallic conductor charge if the length of the conductor is
doubled by stretching it, keeping the applied potential difference constant?
How does drift velocity of electrons in a metallic conductor vary with rise of temperature?
Two wires one of manganin and the other of copper have equal length and equal resistance. Which
one of these wires will be thicker?
Derive expression for drift velocity of electrons in a good conductor in terms of relaxation time of
electrons.
Show that the resistance of a conductor is given by
R = m/ne2 l/A
A battery of emf E and internal resistance r gives of 0.5 A with an external resistance of 12.
Calculate (i) internal resistance of the cell and (ii) emf of the cell.
In a given circuit diagram E1 = 2.0 V, E2 = 6.0 V respectively and resistance r1, r2 and R are 2.0,
4.0 and 10.0 respectively. Calculate the value of current and indicate its direction. Also calculate
the potential difference between the points (i) B and A and (ii) A and C.

C

r1

E1
A
E2

r2

B
R

[2003]
Q.1
Q.2
Q.3
Q.4
Q.5
Q.6
Q.7
Q.8
What are superconductors?
Give two applications of the phenomenon of superconductivity.
Name the temperature of the thermocouple at which its (i) thermo emf change sign and (ii)
thermoelectric power becomes zero.
Out of two bulbs marked 25 W, which has higher resistance?
What is a button cell? Name any two types of button cells.
Define electrical conductivity of a conductor and give its S.I. unit.
What happens to the power dissipation if the value of electric current passing through a conductor of
constant resistance is doubled?
Two heated wires of same dimensions are first connected in series and then in parallel to a source of
supply. What will be the ratio of heat produced in the two cases?
[2004]
Q.1
The diagram shows a piece of pure semiconductor, S
in series with a variable resistor R, and a source of
constant voltage V. Would you increase or decrease
the value of R to keep the reading of ammeter (A)
constant, when semiconductor S is heated? Give
reason.
CBSE TWENTY TWO YEAR PAPERS
(4)
V
S
A
R

AURORA CLASSES
Q.2
Derive condition of balance of a Wheatstone’s bridge.
Q.3
The circuit shown in the diagram contains a battery ‘B’, a rheostat ‘Rh’ and identical lamps P and Q.
What will happen to the brightness of the lamps, if the resistance through the rheostate is increased?
B
Given reasons.
Q
P
Rh
Q.4
Explain with the help of graph the variation of conductivity with temperature for a metallic conductor.

T
Q.5
Deduce the condition for balance in a Wheatstone’s Bridge. Using the principle of Wheatstone’s
bridge, describe the method to determine the specific resistance of a wire in the laboratory. Draw the
circuit diagram and write the formula used.
Write any two important precautions you would observe while performing the experiment.
Q.6
Define the term electrochemical equivalent. Deduce the relation connecting electrochemical
equivalent, chemical equivalent and Faraday.
Q.7
The circuit diagram shows the use of a potentiometer to measure a small emf produced by a
thermocouple connected between X and Y. the cell C, of emf 2.0 V, has negligible internal resistance.
The potentiometer wire PQ is 1.00 m long and has a resistance 5. The balance point S is found to be
400 mm from P. Calculate the value of emf V, generated by the thermocouple.
Cell emf E = 20 V
C
R
S
 
995 
Q
Thermo
Couple
X
G
Y
Hot
Cold
Junction Junction
CBSE TWENTY TWO YEAR PAPERS
(5)
AURORA CLASSES
[2005]
Q.1
Q.2
Q.3
Q.4
Q.5
Q.6
Q.7
Q.8
Sate the principle of potentiometer. Draw a circuit diagram to compare the emf of two primary cells.
Write the formula used. How can the sensitivity of a potentiometer be increased?
Derive an expression for the resistivity of a conductor in terms of number density of free electrons and
relaxation time.
Define the term resistivity and write the S.I. unit.
How does the resistivity of (i) conductor and (ii) a semiconductor vary with temperature?
Draw a graph for the variation of resistivity with temperature for a typical semiconductor.
Draw V-I graphs for ohmic and non-ohmic materials. Give one example of each.
A heating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A
which settles after a few seconds at a steady value of 2.8 A. What is the steady temperature of the
heating element if the room temperature is 27C? Temperature coefficient of resistance of nichrome
averaged over the temperature range involved is 1.7 × 10-4 per C.
Two cells of emf 1.5 and 2 V and internal resistance 1 and 2 respectively are connected in parallel
to pass a current in the same direction through an external resistance of 5.
(i)
Using the circuit diagram.
(ii)
Using Kirchhoff’s laws, calculate the current through each branch of the circuit and potential
difference across 5 resistor.
1 = 1.5 V
A
B
I1
I = I1 +I2
r1 = 1
2 = 2 V
D
I2
E
r2 = 2 C
R=5
F
Q.9
A series battery of 6 lead accumulators each of emf 2.0 V and internal resistance of 0.5 is charged
by a 10 V dc supply. What series resistance should be used in the charging circuit in order W limit the
current to 8A? Using the required resistor, obtain (i) the power supplied by dc source and (ii) the
power dissipated as heat.
Q.10 Two primary cells of emfs wire 1 and 2 (1 > 2) are connected to a potentiometer wire AB as shown
in fig. If the balancing lengths for the two combination of the cells are 250 cm and 40 cm, find the
ratio of 1 and 2.
250
A
E1
400
B
E2
G
G
1
CBSE TWENTY TWO YEAR PAPERS
2
(6)
AURORA CLASSES
Q.11 In a meter bridge, the balance point is found to be 39.5 cm from the end A, when the resistor Y is
12.5 . Determine the resistance of X. Why are the connections between the resistors in meter-bridge
made of copper strips? What happens if the galvanometer and cell are interchanged at the balance
point of the bridge? Would the galvanometer show any current?
[2006]
Q.1
You are given n resistors each of resistance r. They are first connected to get minimum possible
resistance. In these second cases, these are again connected differently to get maximum possible
resistance. Confinite the ratio between minimum and maximum values of resistance so obtained.
Q.2
A 10 m long wire of uniform cross-section and 20 resistances is used in a potentiometer. The wire is
connected in series with a battery of 5V along with an external resistance of 480. If an unknown emf
E is balanced at 6.0 m length of the wire, calculate:
(i)
The potential gradient of the potentiometer wire.
(ii)
The value of unknown emf E.
Q.3
Sketch the graph showing the variation of resistivity of carbon with temperature.
Q.4
Write the mathematical relation between mobility and drift velocity of charge carries in a conductor.
Name the mobile charge carries responsible for conduction of electric current in
(i)
an electrolyte
(ii)
an ionized gas.
E1
Q.5
E2
Two cells E1 and E2 in the given circuit diagram have an EMF
of 5V and 9V and internal resistance of 0.3 and 1.2 
respectively. Calculate the value of current flowing through the
resistance of 3.
4.6
6
3
Q.6
The variation of potential difference V with length  in case of two potentiometer P and Q is as
shown. Which one of these two will you prefer for comparing EMFs of two primary cells?
P
V
Q
t
Q.7
Q.8
Which one of the two, an ammeter or a miliammeter has a higher resistance and why?
Draw a circuit diagram of a Metre Bridge and write the mathematical relation used to determine the
value of an umknown resistance. Why cannot such an arrangement be used for measuring very low
resistance?
[2007]
Q.1
A voltage of 30V is applied across a carbon resistor with first, second and third rings of blue, black
and yellow colours respectively. Calculate the value of current, in mA, through the resistor.
CBSE TWENTY TWO YEAR PAPERS
(7)
AURORA CLASSES
Q.2
Q.3
A galvanometer has a resistance of 30. It gives full-scale deflection with a current of 2 mA.
Calculate the value of the resistance needed to convert it into an ammeter of range 0 – 0.3 A.
For the potentiometer circuit shown in the given figure, points ‘X’ and ‘Y’ represent the two terminals
of an unknown emf ‘E’. A student observed that when the jockey is moved form the end ‘A’ to the
end ‘B’ of the potentiometer wire, the deflection in the galvanometer remains in the same direction.
What may be the two possible faults in the circuit that could result in this observation?
If the galvanometer deflection at the end ‘B’ is
E
(
.)
A
E
(i)
(ii)
B
G
 
X
Y
more
less than that at the end ‘A’, which of the two faults, listed above, would be there in the
circuit? Give reasons in support of your answer in each case?
or
The given figure shows a network of resistance R1, R2, R3 and R4.
B
R2
R1
A
R3
R4
D
Q.4
Q.5
Q.6
2V
Using Kirchhoff’s laws, establish the balance condition for the network.
What is Seeback effect? Plot a graph showing the variation of thermo emf with temperature of hot
junction (keeping cold junction at 0C) of a thermocouple. How will the
(i)
neutral temperature,
(ii)
inversion temperature of a thermocouple change when the temperature of cold junction is
increased?
Write the mathematical relation for the resistivity of a material in terms of relaxation time, number
density, and mass and charge of charge carriers in it. Explain using this relation, why the resistivity of
a metal increases and that of a semiconductor decreases with rise in temperature.
A cylindrical metallic wire is stretched to increase its length by 10% Calculate the percentage increase
in its resistance.
[2008]
Q.1
The metallic wire of the same material have the same length but cross-sectional area is in the ratio
1 : 2. They are connected (i) in series and (ii) in parallel. Compare the drift velocities of electrons in
the two wires in both the cases (i) and (ii).
CBSE TWENTY TWO YEAR PAPERS
(8)
AURORA CLASSES
Q.2
Q.3
Q.4
Q.5
Q.6
Q.7
(i)
(ii)
(iii)
Derive an expression for the resistivity of a good conductor. In terms of the relasation time of
electrons?
(i)
Calculate the equivalent resistance of the given electrical network between points A and B.
(ii)
Also calculate the current through CD and ACB, if a 10 V d.c source is connected
between A and B and the value of R is assumed as 2 .
Two wires X, Y have the same resistivity but their cross-sectional areas are in the ratio 2 : 3 and
length in the ratio 1 : 2. They are first connected in series and then in parallel to a d.c. source. Find out
the ratio of the drift speeds of the electrons in the two wires for the two cases.
Prove that the current density of a metallic conductor is directly proportional to the drift speed of
electrons.
n-identical cells, each of emf , internal resistance r connected in series are charged by a d.c, source of
`, using a resistance R.
(i)
Draw the circuit
(ii)
Deduce expressions for (a) the charging current and (b) the potential difference across the
combination of cells.
A potentiometer wire of length 1 m is connected to a driver cell of emf 3 V as shown in the figure.
When a cell of emf 1.5 V is used in the secondary circuit, the balance point is found to be 60 cm. On
replacing this cell by a cell of unknown emf, the balance point shifts to 80 cm.
Calculate unknown emf of the cell.
Explain with reason, whether the circuit works if the driver cell is replaced with a cell of emf 1V.
Does the high resistance R, used in the secondary circuit affect the balance point? Justify your answer.
3V
J
A
B
1.5 V

[2009]
Q.1
Q.2
Q.3
Q.4
Define electric flux. Write its S.I unit. A charge q is enclosed by a spherical surface of radius R. If the
radius is reduced to half, how would the electric flux through the surface change?
[2]
Calculate the current drawn from the batter in the given network.
[2]
A wire of 20  resistances is gradually stretched to double its original length. It is then cut into two
equal parts. These parts are then connected in parallel across a 4.0 volt battery. Find the current drawn
from the battery.
[2]
Draw 3 equipotential surfaces corresponding to a field that uniformly increases in magnitude but
remains constant along Z-direction. How are these surfaces different from that of a constant electric
field along Z-direction?
[2]
CBSE TWENTY TWO YEAR PAPERS
(9)
AURORA CLASSES
Q.5
(i)
(ii)
State the principal of working of a meter bridge.
In a meter bridge balance point is found at a distance l1 with resistances Rand S as shown in
the figure.
[3]
When an unknown resistance X is connected in parallel with the resistance S, the balance point shifts
to a distance 2. Find the expression for X in terms of 1, 2 and S.
[3]
[2010]
Q.1
State Kirchhoff’s rules. Use these rules to write the expression for the currents I1, I2 and I3 in the
circuit diagram shown.
[3]
I1
I2
I3
Q.2
E1 =2V
r1=4 
E2 =1V
r2=3 
E3= 4V
r3=2 
Two conducting wires X and Y of same diameter but different materials are joined in series across a
battery. If the number density of electrons in X is twice that in Y, the ratio of drift velocity of
electrons in the two wires.
[1]
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(10)
AURORA CLASSES
Q.3
Write any two factors on which internal resistance of a cell depends. The reading on a high resistance
voltmeter, when a cell is connected across it, is 2.2 V. When the terminals of the cell are also
connected to a resistance of 5 ohm as shown in the circuit, the voltmeter reading drops to 1.8 V. Find
the internal resistance of the cell.
[3]
+ V
_
+
_
R=5
K
[2011]
Q.1
In the given circuit, assuming point A to be at zero potential, use Kirchhoff’s rules to determine the
potential at point B.
[2]
2V
1A
B
2
R
A
Q.2
2A
D
C
1V
R1
2A
In the meter bridge experiment, balance point was observed at J with AJ = .
(i)
The values of R and X were doubled and then interchanged. What would be the new
position of balance point?
(ii)
If the galvanometer and battery are interchanged at the balance position, how will the balance
point get affected?
[2]
R
X
G
A
Q.3
B
J
Two heating elements of resistance R1 and R2 when operated at a constant supply of voltage, V,
consume powers P1 and P2 respectively. Deduce the expressions for the power of their combination
when they are, in turn connected in (i) series and (ii) parallel across the same voltage supply.
[3]
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(11)
AURORA CLASSES
[2012]
Q.1
Q.2
Q.3
Two wires of equal length, one of copper and the other of manganin have the same resistance.
Which wire is thicker?
[1]
Calculate the value of the resistance R in the circuit shown in the figure so that the current in the
circuit is 0.2 A. What would be the potential difference between points A and B?
[3]
Define relaxation time of the free electrons drafting in a conductor. How is it related to the drift
velocity of free electrons? Use this relation to deduce the expression for the electrical resistivity of the
material.
[3]
[2013]
Q.1
Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel with
each other across an external resistance R. What is the current through this resistance?
Q.2
Explain the term 'drift velocity' of electrons in a conductor. Hence obtain the expression for the
current through a conductor in terms of 'drift velocity'.
OR
Describe briefly, with the help of a circuit diagram, how a potentiometer is used to determine the
internal resistance of a cell.
Q.3
Define the current sensitivity of a galvanometer. Write its S.L unit. Figure shows two circuits each
having a galvanometer and a battery of 3 V. When the galvanometers in each· arrangement do not
show any deflection, obtain the ratio R1/R2.
[2014]
Q.1
Why is the use of a.c. voltage preferred over d.c. voltage? Give two reasons.
Q.2
A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable resistor ‘R’. Plot a graph
showing variation of terminal voltage ‘V’ of the cell versus the current ‘T’. Using the plot, show how
the emf of the cell and its internal resistance can be determined.
Q.3
Estimate the average drift, speed of conduction electrons in a copper wire of cross-sectional area 1.0 ×
10-7 m2 carrying a current of 1.5 A. Assume the density of conduction electrons to be 9 × 1028 m-3 .
(a)
Draw a labeled diagram of a moving coil galvanometer. Describe briefly its principle and
working.
(b)
Answer the following :
(i)
Why is it necessary to introduce a cylindrical soft iron core inside the coil of
galvanometer?
(ii)
Increasing the current sensitivity of a galvanometer may not necessarily increase its
voltage sensitivity. Explain, giving reason.
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a
AURORA CLASSES
Q.4
Answer the following :
(a)
Why are the connections between the resistors in a meter bridge made of thick copper strips?
(b)
Why is it generally preferred to obtain the balance point in the middle of the meter
bridge wire?
(c)
Which material is used for the meter bridge wire and why?
Or
A resistance of R  draws current from a potentiometer as shown in the figure. The potentiometer has
a total resistance R0. A voltage V is supplied to the potentiometer. Derive an expression for the
voltage across R when the sliding contact is in the middle of the potentiometer.
CBSE TWENTY TWO YEAR PAPERS
(13)
AURORA CLASSES
SAMPLE PAPER
Q.1
Q.2
Under what condition is the heat produced in an electric circuit
(i)
directly proportional
(ii)
inversely proportional to the resistance of the circuit?
A resistor ‘R’ is put in series with a voltmeter having electrodes made from a metal of chemical
equivalent ‘E’. A mass ‘m’ of the metal gets deposited in a time‘t’ when a current is made to flow
through the combination. Obtain an expression for the heat produced in the resistor during this time?
For the potentiometer circuit shown in the given figure, points ‘X’ and ‘Y’ represent the two terminals
of an unknown emf ‘E’. A student observed that when the jockey is moved form the end ‘A’ to the
end ‘B’ of the potentiometer wire, the deflection in the galvanometer remains in the same direction.
What are the two possible faults in the circuit that could result in this observation?
If the galvanometer deflection at the end ‘B’ is
E
( )
.
A

X
E

B
G
Y
more
less than that at the end ‘A’, which of the two faults, listed above, would be there in the
circuit? Give reasons in support of your answer in each case?
Give the nature of V- I graph for
(i) ohmic (ii) non- ohmic
current elements? Give one example of each type?
The given figure shows a network of resistances. Name the circuit so formed. What is the current
flowing in the arm BD of this circuit? State the two laws used to find the current in different branches
of this circuit?
B
20 
10 
(i)
(ii)
Q.3
Q.4
A
50 
60 
30 
D
Q.5
Q.6
Q.7
2V
Explain the cause of production of emf when the two junctions of two dissimilar metals are
maintained at different temperatures.
With the cold junction at ‘0oC’, the natural temperature for a thermo-couple is obtained at ‘270oC’.
The cold junction temperature is now lowered to ‘–10oC’. Obtain the
(i)
neutral temperature
(ii)
the temperature of inversion in this case.
What is the role of MnO2 in a dry cell?
A wire of resistivity ‘’ is stretched to three time’s its length. What will be its new resistively?
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AURORA CLASSES
Q.8
Q.9
Q.10
Q.11
Q.12
Q.13
Q.14
Q.15
A series battery of 10 lead accumulators each of emf 2V and internal resistance 0.25 ohm is charged
by a 220V D.C. source. To limit the charging current a resistance of 47.5 ohm is used in series in the
charging circuit. What is
(i)
the power supplied by D.C. source and
(ii)
power dissipated as heat? Account for the difference of power in (a) and (b).
A galvanometer coil has a resistance of 30 ohm and the meter shows full-scale deflection for a current
of 2.0 mA. Calculate the value of resistance required to convert it into an ammeter of range 2.0A?
Also calculate the net resistance of the ammeter?
Two wires ‘A’ and ‘B’ of the same material and having same length. Have there cross sectional area
in the ratio 1: 4. What would be the ratio of heat produced in these wires when same voltage is applied
across each?
Observations on a given device yielded the following current-voltage data.
Current
Voltage
Current
Voltage
(Amperes)
(Volts)
(Amperes)
(volts)
1.0
19.7
4.0
78.8
2.0
39.4
5.0
98.5
3.0
59.1
Draw V-I graph using the above data? What conclusion can you draw form the graph with regard to
ohmic or non-ohmic nature of the device?
A wire of resistance ‘4R’ is bent in the form of a circle. What is the effective resistance between the
ends of any diameter of the circle?
With the help of a circuit diagram explain how can you find the internal resistance of a primary cell?
Derive the necessary formula?
A student has two wires, one of iron and the other of copper. Both the wires are of equal length and
diameter. He first joins the two wires in series and passes electric current through the combination,
which increases gradually. After that he joins the two wires in parallel and repeats the process of
passing current. Which wire will glow first in each case and why?
For a thermocouple, name the temperature at which its
(i)
thermo emf changes its sign.
0.16
Resistance
(ii)
thermo electric power becomes zero.
(ohms)
0.06
0 2 4 6
Q.16 The given graph shows the variation of resistance of mercury with
temperature. Name the phemomenon shown by mercury in the
Temperature
temperature range 0<T <4k. Give one possible application of this
(Kelvin)
phenomenon?
Q.17 A household circuit has a fuse of 5A rating. Calculate the maximum number of bulbs of rating
60W –220 V each that can be connected in this household circuit?
3
Q.18 The V-I graphs of two resistors, and their series combination,
2
I
1
are shown in the adjoining figure. Which one on these
graphs represents the series combination of the other two?
Give reasons for your answer.
V
Q.19 A voltmeter of resistance ‘RV’ and an ammeter of
resistance ‘RA’ are connected in a circuit to measure a
resistance ‘R’ as shown in the figure. The ratio of the
A
meter readings gives an apparent resistance ‘R’. Show
E
that ‘R’ and ‘R’ are related by the relation.
R
1/R = 1/R - 1/RV
V
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AURORA CLASSES
Q.20 Name any two types of button cell?
Q.21 Name one ohmic material and one non-ohmic device? Draw V–I graph for each?
Q.22 In the given circuit diagram, calculate the value of ‘R’ using Kirchoff’s laws?
2A

10V
E
R
2.5
4
1A
Q.23 In a part of the circuit shown in the figure, the rate of heat dissipation in 4 resistors is 100J/s.
Calculate the heat dissipated in the 3 resistors in 10 seconds?
R1
R2
4
2
R3
Q.24
Q.25
Q.26
Q.27
Q.28
Q.29
Q.30
Q.31
Q.32
Q.33
Q.34
A copper voltmeter and a bulb of rating 100W –220V are connected in series across a DC supply. If
0.198g of copper is deposited on the electrode in 40 minutes, calculate the potential difference across
the bulb assuming that its resistance is approximately constant. E.C.E of copper =0.00033g/C?
Two metallic wires of the same material and same length but different cross sectional areas are joined
together (i) in series (ii) in parallel, to source of emf. In which of the two wires will the drift – velocity
of electron be more in each of the two cases and why?
Two electric bulbs are rated as 220V –100W & 220V –60W. Which one of these has greater
resistance and why?
How does one remove the defect of polarization in a
(i) Daniel cell
(ii) Leclanche cell
Write the chemical equation for charging in
(i) lead accumulator
(ii) Alkali accumulator
Will the drift speed of free electrons in a metallic conductor increase of decrease with the increase in
its temperature?
The variation of p.d with length in case of two potentiometers A and B is given below. When of the
tow is more sensitive?
State Kirchoff’s laws for an electric network.
A simple Voltaic cell has a n e.m.f. of 1.0 V. Is there a net field inside the cell when (i) circuit is open
(ii) circuit is closed and steady current is drawn from it. Explain you answer in each case.
What is seeback effect? Draw a curve to show the variation of thermo-emf with the gradual increase
in the temperature of hot junction. Mark the neutral temperature and temperature of inversion of the
thermocouple on the curve.
A steady current flows in a metallic conductor of non-uniform cross-section. Which of the following
quantities is/are constant along the conductor: Current, current density, drift speed.
Explain how the average velocity of free electrons in a metal at constant temperature, in an electric
field, remain constant even though the electrons are being constantly accelerated by this electric field?
Two students X and Y perform an experiment on potentiometer separately using the circuit diagram
shown here.
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AURORA CLASSES
Keeping other things unchanged
(i)
X increases the value of distance R
(ii)
Y decreases the value of resistance S in the set up.
How would these changes affect the position of null point in each case and why?
Q.35 12 cells, each of emf 1.5V and internal resistance , are arranged in m rows each containing n cells
connected in series, as shown. Calculate the values of n and m for which this combination would send
maximum current through an external resistance of 15 .
Q.36 The I-V characteristics of a resistor are observed to deviate from a straight line for higher values of
current as shown below. Why?
Q.37 A cell of unknown emf E and internal resistance r, two unknown resistances R 1 and R2 (R2 >R1) and a
perfect ammeter are given. The current in the circuit is measured in five different situations :
(i)
Without any external resistance in the circuit,
(ii)
With resistance R1 only,
(iii) With resistance R2 only,
(iv)
With both R1 and R2 used in series combination and (v) With R1 and R2 used in parallel
combination. The current obtained in the five cases are 0.42A, 0.6A, 1.05A, 1.4A, and 4.2A,
but not necessarily in that order. Identify the currents in the five cases listed above and
calculate E, r,, R1 and R2.
Q.38 Six equal resistors, each of value ‘R’, joined together as shown in figure. Calculate the equivalent
resistance across ‘AB’. If a supply of emf ‘E’ is connected across ‘AB’, compute the current through
the arms ‘DE’ and ‘AB’?
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AURORA CLASSES
R
A
C
R
R
B
R
D
R
E
R
F
Q.39 Describe the formula for the equivalent EMF and internal resistance for the parallel combination of
two cells with EMF E1 and E2 and internal resistances r1 and r2 respectively. What is the corresponding
formula for the series combination? Two cells of EMF 1V, 2V and internal resistances 2 and 1
respectively are connected in
(i)
series,
(ii)
parallel.
What should be the external resistance in the circuit so that the current through the resistance be the
same in the two cases? In which case more heat is generated in the cells?
Q.40 For the circuit shown here, calculate the potential difference between points B and D
Q.41 State the steady value of the reading of the ammeter in the circuit shown below.
[1]
Q.42 For the circuit shown here, would the balancing length increase, decrease or remain the same, if
(i)
(ii)
R1 is decreased
R2 is increased
without any other change, (in each case) in the rest of the circuit. Justify your answers in each
case.
[2]
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AURORA CLASSES
Q.43 The galvanometer, in each of the two given circuits, does not show any deflection. Find the ratio of
the resistors R1 and R2, used in these two circuits.
[3]
Q.44 A current I flows through a wire of radius ‘r’ and the drift velocity ‘vd’. What is the drift velocity of
electrons through a wire of same material but having double the radius, when a current ‘2I’ flows
through it?
[1]
Q.45 The graph of variation of resistance R of a metal wire as a function of its diameter D is as follows.
Give the reason for the shape of the graph.
[1]
Q.46 Three resistors of resistance ‘r’ each are connected to get maximum possible resistance. Then they are
connected differently to get minimum possible resistance. Find the ratio between minimum and
maximum resistance so obtained.
[2]
Q.47 State the principle behind working of a potentiometer? The circuit diagram shows the use of a
potentiometer to measure a small emf produced by a thermocouple connected between X and Y. A
cell of emf 2V has negligible internal resistance. The potentiometer wire PQ is 1 m long and has
resistance 5Ω. The balance point S is found to be 40cm from P.
Calculate the value of emf generated by the thermocouple.
[3]
Q.48 A 60W bulb is connected to 220 V supply. How much current does it draw?
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AURORA CLASSES
Q.49 A piece of wire is redrawn by pulling it until its length is doubled .Compare the new resistance with
the original value.
Q.50 What is the equivalent resistance between terminals A and C of the given circuit?
Q.51 The ends of a resistance are connected to 19 cells in series, each of internal resistance 0.1 ohm. The
current is found to be 2A. The number of cells is reduced to 15 and an extra resistance of 9.5 ohm is
connected in series to the given resistance. The current becomes half. Find the given resistance and
the emf of each cell.
Q.52 A resistance R is connected across a cell, of Emf E, and internal resistance r. A potentionter now
measures the p.d, between the terminals of the cell, as V. State the expression for ‘r’ in terms of E, V
and R.
Q.53 In the meter bridge experiment, a student observed a balance point at the point J, where AJ = I. Draw
the equivalent Wheat stone Bridge circuit diagram for this set up.
The values of R and X are both doubled and then interchanged. What would be the new position of the
balance point ? If, in this set up, the galvanometer and battery are interchanged at the balance point
position, how will the balance point get affected?
Q.54 A parallel combination of two cells of Emf’s E1 & E2, and internal resistances r, and r2, is used to
supply currents to a load of resistance R. Write the expression for the current through the load in terms
of E1, E2r1 and r2.
Q.55 Write the nature of path of free electrons in a conductor in the
(i)
presence of electric field
(ii)
absence of electric field.
eE
t .
m
What is the average velocity of a free electron in the presence of an electric field? Do all electrons
have the same average velocity?
Between two successive collisions each free electron acquires a velocity from 0 to V where V =
Q.56 A potentiometer circuit is set up as shown. The potential gradient across the potentiometer wire is
0.025 V/cm and the ammeter present in the circuit reads 0.1 A, when the two way key is completely
switched off. The balance points, when the key between the terminals (i) 1 & 2 (ii) 1 & 3, is plugged
in, are found to be at lengths 40 cm and 100 cm respectively. Find the values of R and X.
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AURORA CLASSES
Q.57 Draw that the current versus potential difference characteristics for a cell. How can the internal
resistance of the cell be determined from this graph?
Q.58 Is current density a vector or scalar quantity? Deduce the relation between current density and
potential difference across a current carrying conductor of length I, area of cross-section A,
and
number density of free electrons n. How does the current density, in a conductor vary with
(a)
incrase in potenital gradient ?
(b)
increase in temperature?
(c)
increase in length?
(d)
increase in area of cross-section?
(Assume that the other factors remain constant in ear case.)
OR
Write the condition of balance in Wheatstone bridge. In the given Wheatstone bridge, the current in
the resistor 3R, is zero. Find the value of R, if the carbon resistor, connected in one arm of the bridge,
has the colour sequence of red, red and orange.
The resistances, of BC and CD arms are now interchanged and another carbon resistance is connected
in place of R so that the current through the arm BD is again zero. Write the sequence of colour bands
of this carbon resistor. Also find the value of current through it.
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AURORA CLASSES