question_answer 1)
Directions : (1-5) Electric Current and Current Density The flow of charge in a particular direction constitutes the electric current. Current is measured in Ampere. Quantitatively, electric current in a conductor across an area held perpendicular to the direction of flow of charge is defined as the amount of charge flowing across that area per unit time. Current density at a point in a conductor is the ratio of the current at that point in the conductor to the area of cross section of the conductor of that point. The given figure shows a steady current flows in a metallic conductor of non-uniform cross section. Current density depends inversely on area so here \[{{J}_{1}}>{{J}_{2}}\] as \[{{A}_{1}}<{{A}_{2}}\]
What is the current flowing through a conductor, if one million electrons are crossing in one millisecond through a cross-section of it?
A)
\[2.5\,\,\times {{10}^{-10}}A\] done
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B)
\[1.6\times {{10}^{-10}}A\] done
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C)
\[7.5\times {{10}^{-9}}A\] done
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D)
\[8.2\times {{10}^{-11}}A\] done
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question_answer 2)
SI unit of electric current is:
A)
C s done
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B)
\[N\,\,{{s}^{-2}}\] done
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C)
\[C\,{{s}^{-1}}\] done
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D)
\[{{C}^{-1}}\,\,{{s}^{-1}}\] done
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question_answer 3)
A steady current flows in a metallic conductor of non-uniform cross section. Which of these quantities is constant along the conductor?
A)
Electric field done
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B)
Drift velocity done
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C)
Current done
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D)
Current density done
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question_answer 4)
A constant current I is flowing along the length of a conductor of variable cross-section as shown in the fig. The quantity which does not depend upon the area of cross-section is :
A)
electron density done
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B)
current density done
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C)
drift velocity done
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D)
electric field done
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question_answer 5)
When a current of 40 A flows through a conductor of area \[10\text{ }{{m}^{2}}\], then the current density is :
A)
\[4\text{ }A/{{m}^{2}}\] done
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B)
\[1\text{ }A/{{m}^{2}}\] done
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C)
\[2\text{ }A/{{m}^{2}}\] done
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D)
\[8\text{ }A/{{m}^{2}}\] done
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question_answer 6)
Directions : (6-10) Factors Affecting Resistance According to Ohm's law, the current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor i.e. \[I\propto V\]\[\Rightarrow \,\frac{V}{I}=R\], where R is resistance of the conductor. Electrical resistance of a conductor is the obstruction posed by the conductor to the flow of electric current through it. It depends upon length, area of cross-section, nature of material and temperature of the conductor. We can write, \[R\propto \frac{l}{A}\]or\[R=\rho \frac{l}{A}\], where p is electrical resistivity of the material of the conductor.
Dimensions of electric resistance is :
A)
\[\left[ M{{L}^{2}}{{T}^{-2}}{{A}^{-2}} \right]\] done
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B)
\[\left[ M{{L}^{2}}\,{{T}^{-3}}\,{{A}^{-2}} \right]\] done
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C)
\[\left[ {{M}^{-1}}\,{{L}^{-2}}\,{{T}^{-1}}\,A \right]\] done
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D)
\[\left[ {{M}^{-1}}\,{{L}^{2}}\,{{T}^{2}}\,{{A}^{-1}} \right]\] done
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question_answer 7)
If \[1\mu A\] current flows through a conductor when potential difference of 2 volt is applied across its ends, then the resistance of the conductor is :
A)
\[2\times {{10}^{6}}\Omega \] done
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B)
\[3\times {{10}^{5}}\Omega \] done
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C)
\[1.5\times {{10}^{5}}\Omega \] done
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D)
\[5\times {{10}^{7}}\Omega \] done
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question_answer 8)
Specific resistance of a wire depends upon :
A)
length done
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B)
cross-sectional area done
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C)
mass done
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D)
none of these done
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question_answer 9)
The slope of the graph between potential difference and current through a conductor is :
A)
a straight line done
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B)
curve done
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C)
first curve then straight line done
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D)
first straight line then curve done
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question_answer 10)
The resistivity of the material of a wire 1.0m long 0.4 mm in diameter and having a resistance of 2.0 ohm is :
A)
\[1.57\times {{10}^{-6}}\Omega \,m\] done
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B)
\[5.25\times {{10}^{-7}}\Omega \,m\] done
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C)
\[7.12\times {{10}^{-5}}\Omega \,m\] done
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D)
\[2.55\times {{10}^{-7}}\Omega \,m\] done
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question_answer 11)
Directions : (11-15)
Temperature Dependence of Resistivity
The resistance of a conductor at temperature \[t{}^\circ C\] is given by \[{{R}_{t}}={{R}_{0}}\left( 1+\alpha t \right)\]
Where \[{{R}_{t}}\] is the resistance at \[t{}^\circ C\], \[{{R}_{0}}\] is the resistance at \[0{}^\circ C\] and \[\alpha \] is the characteristics constants of the material of the conductor.
Over a limited of range of temperatures, that is not too large. The resistivity of a metallic conductor is approximately given by \[{{\rho }_{t}}={{\rho }_{0}}\left( 1+\alpha t \right)\].
Where \[\alpha \] is the temperature coefficient of resistivity. Its unit is \[{{K}^{-1}}\]or \[{}^\circ {{C}^{-1}}\].
For metals \[\alpha \] is positive i.e., resistance increases with rise in temperature.
For insulators and semiconductors, \[\alpha \] is negative i.e., resistance decreases with rise in temperature.
Fractional increase in resistivity per unit increse in temperature is defined as :
A)
resistivity done
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B)
temperature coefficient of resistivity done
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C)
conductivity done
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D)
drift velocity done
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question_answer 12)
The material whose resistivity is insensitive to temperature is :
A)
silicon done
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B)
copper done
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C)
silver done
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D)
nichrome done
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question_answer 13)
The temperature coefficient of the resistance of a wire is 0.00125 per\[{}^\circ C\]. At 300 K its resistance is 1 ohm. The resistance of wire will be 2 ohms at:
A)
1154 K done
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B)
1100 K done
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C)
1400 K done
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D)
1127K done
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question_answer 14)
The temperature coefficient of resistance of an alloy used for making resistors is :
A)
small and positive done
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B)
small and negative done
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C)
large and positive done
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D)
large and negative done
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question_answer 15)
For a metallic wire the ratio V/I (V = applied potential difference and I = current flowing) is:
A)
independent of temperature done
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B)
increases as the temperature rises done
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C)
decreases as the temperature rises done
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D)
increases or decreases as temperature rises depending upon the metal. done
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question_answer 16)
Directions : (16-20) Relation between V, \[\varepsilon \] and r of a cell Emf of a cell is the maximum potential difference between two electrodes of the cell when no current is drawn from the cell. Internal resistance is the offered by the electrolyte of a cell when the resistance electric current flows through it. The internal resistance of a cell depends upon the following factors; (i) distance between the electrodes (ii) nature and temperature of the electrolyte (iii) nature of electrodes (iv) area of electrodes. For a freshly prepared cell, the value of internal resistance is generally low and goes on increasing as the cell is put to more and more use. The potential difference between the two electrodes of a cell in a closed circuit is called terminal potential difference and its value is always less than the e.m.f. of the cell in a closed circuit. It can be written as\[V=\varepsilon -Ir\].
The terminal potential difference of two electrodes of a cell is equal to emf of the cell when:
A)
\[I\ne 0\] done
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B)
\[I=0\] done
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C)
both [a] and [b] done
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D)
neither [a] nor [b] done
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question_answer 17)
A cell of emf s and internal resistance r gives a current of 0.5 A with an external resistance of \[12\,\Omega \] and a current of 0.25 A with an external resistance of \[25\,\,\Omega \]. What is the value of internal resistance of the cell?
A)
\[5\,\Omega \] done
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B)
\[1\,\Omega \] done
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C)
\[7\,\Omega \] done
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D)
\[3\,\Omega \] done
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question_answer 18)
Choose the wrong statement :
A)
Potential difference across the terminals of a cell in a closed circuit is always less than its emf. done
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B)
Internal resistance of a cell decrease with the decrease in temperature of the electrolyte. done
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C)
Potential difference versus current graph for a cell is a straight line with a -ve slope. done
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D)
Terminal potential difference of the cell when it is being charged is given as\[V=\varepsilon +Ir\]. done
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question_answer 19)
An external resistance R is connected to a cell of internal resistance r, the maximum current flows in the external resistance when
A)
\[R=r\] done
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B)
\[R<r\] done
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C)
\[R>r\] done
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D)
\[R=1/r\] done
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question_answer 20)
If external resistance connected to a cell has been increased to 5 times, the potential difference across the terminals of the cell increases from 10 V to 30 V. Then, the emf of the cell is :
A)
30V done
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B)
60 V done
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C)
50 V done
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D)
40 V done
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question_answer 21)
Directions : (21-25) Mechanism of Current flow in a conductor Metals have a large number of free electrons nearly \[{{10}^{28}}\] per cubic metre. In the absence of electric field, average terminal speed of the electrons in random motion at room temperature is of the order of \[{{10}^{5}}\,m{{s}^{-1}}\]. When a potential difference V is applied across the two ends of a given conductor, the free electrons in the conductor experiences a force and are accelerated towards the positive end of the conductor. On their way, they suffer frequent collisions with the ions/atoms of the conductor and lose their gained kinetic energy. After each collision, the free electrons are again accelerated due to electric field, towards the positive end of the conductor and lose their gained kinetic energy in the next collision with the ions/atoms of the conductor. The average speed of the free electrons with which they drift towards the positive end of the conductor under the effect of applied electric field is called drift speed of the electrons.
Magnitude of drift velocity per unit electric field is :
A)
current density done
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B)
current done
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C)
resistivity done
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D)
mobility done
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question_answer 22)
The drift speed of the electrons depends on
A)
dimensions of the conductor done
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B)
number density of free electrons in the conductor done
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C)
both [a] and [b] done
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D)
neither [a] nor [b] done
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question_answer 23)
We are able to obtain fairly large currents in a conductor because :
A)
the electron drift speed is usually very large done
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B)
the number density of free electrons is very high and this can compensate for the low values of the electrons drift speed and the very small magnitude of the electron charge done
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C)
the number density of free electrons as well as the electron drift speeds are very large and these compensate for the very small magnitude of the electron charge done
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D)
the very small magnitude of the electron charge has to be divided by the still smaller product of the number density and drift speed of get the electric current. done
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question_answer 24)
Drift speed of electrons in a conductor is very small i.e. \[i={{10}^{-4}}\,m{{s}^{-1}}\]. The electric bulb glows immediately. when the switch is closed because :
A)
drift velocity of electron increases when switch is closed done
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B)
electrons are accelearated towards the negative end of the conductor done
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C)
the drifting of electrons takes place at the entire length of the conductor done
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D)
the electrons of conductor move towards the positive end and protons of conductor move towards negative end of the conductor. done
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question_answer 25)
The number density of free electrons in a copper is \[8.5\times {{10}^{28}}\,{{m}^{-3}}\]. How long does an electron take to drift from one end of a wire 3.0 m long to its other end ? The area of cross-section of the wire is \[2.0\times {{10}^{-6}}\,{{m}^{2}}\] and it is carrying a current of 3.0 A.
A)
\[8.1\times {{10}^{4}}s\] done
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B)
\[2.7\times {{10}^{4}}s\] done
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C)
\[9\times {{10}^{3}}s\] done
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D)
\[3\times {{10}^{3}}s\] done
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question_answer 26)
Directions : (26-30)
Grouping of Cells
A single cell provides a feeble current. In order to get a higher current in a circuit, we often use a combination of cells. A combination of cells is called a battery. Cells can be joined in series, parallel or in a mixed way.
Two cells are said to be connected in series when negative terminal of one cell is connected to positive terminal of the other cell and so on. Two cells are said to be connected in parallel if positive terminal of each cell is connected to one point and negative terminal of each cell connected to the other point. In mixed grouping of cells, a certain number of identical cells are joined in series and all such rows are then connected in parallel with each other.
To draw the maximum current from a combination of cells, how should the cells be grouped ?
A)
Parallel done
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B)
series done
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C)
Mixed grouping done
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D)
Depends upon the relative values of internal and external resistances. done
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question_answer 27)
The total emf of the cells when n identical cells each of emf \[\varepsilon \] are connected in parallel is :
A)
\[n\varepsilon \] done
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B)
\[{{n}^{2}}\varepsilon \] done
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C)
\[\varepsilon \] done
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D)
\[\frac{\varepsilon }{n}\] done
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question_answer 28)
4 cells each of emf 2V and internal resistance of \[1\Omega \] are connected in parallel to a load resistor of \[2\Omega \]. Then the current through the load resistor is :
A)
2A done
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B)
1.5 A done
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C)
1A done
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D)
0.888 A done
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question_answer 29)
If two cells out of n number of cells such of internal resistance 'r' are wrongly connected in series, then total resistance of cell is :
A)
2nr done
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B)
nr - 4r done
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C)
nr done
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D)
r done
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question_answer 30)
Two identical non-ideal batteries are connected in parallel. Consider the following statements. (i) The equivalent e.m.f. is smaller than either of the two e.m.f. (ii) The equivalent internal resistance is smaller than either of the two internal resistances
A)
Both (i) and (ii) are correct done
clear
B)
(i) is correct but (ii) is wrong done
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C)
(ii) is correct but (i) is wrong done
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D)
Both (i) and (ii) are wrong. done
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question_answer 31)
Directions : (31-35)
Kirchhoff's Rules
In 1942, a German physicist Kirchhoff extended Ohm's law to complicated circuits and gave two laws, which enable us to determine current in any part of such a circuit.
According to Kirchhoff's first rule, the algebraic sum of the current meeting at a junction in a closed electric circuit is zero. The current flowing in a conductor towards the junction is taken as positive and the current flowing away from the junction is taken as negative.
According to Kirchhoff s second rule, in a closed loop the algebraic sum of the emfs and algebraic sum of the products of current and resistance in the various arms of the loop is zero. While traversing a loop, if negative pole of the cell is encountered first, then its e.m.f. is negative, otherwise positive..
Kirchhoff's Ist law follows :
A)
law of conservation of energy done
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B)
law of conservation of charge done
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C)
law of conservation of momentum done
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D)
Newton's third law of motion done
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question_answer 32)
The value of current I in the given circuit is :
A)
4.5 A done
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B)
3.7 A done
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C)
2.0 A done
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D)
2.5 A done
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question_answer 33)
Kirchhoff s IInd law is based on :
A)
law of conservation of momentum of electron done
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B)
law of conservation of charge and energy done
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C)
law of conservation of energy done
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D)
none of these done
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question_answer 34)
Point out the right statements about the validity of Kirchhoff s junction rule :
A)
The current flowing towards the junction are taken as positive. done
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B)
The current flowing away from the junction are taken as negative. done
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C)
bending or reorienting the wire does not change the validity of Kirchhoff's junction rule. done
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D)
All of the above. done
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question_answer 35)
Potential difference between A and B in the circuit shown here is :
A)
4 V done
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B)
5.6 V done
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C)
2.8 V done
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D)
6 V done
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question_answer 36)
Directions : (36-40) Wheatstone Bridge and Its Applications Wheatstone bridge is an arrangement of four resistances P, Q, R and S connected as shown in the figure. Their values are so adjusted that the galvanometer G shows no deflection. The bridge is then said to be balanced when this condition is achieved. In the setup shown here, the points B and D are at the same potential and it can be shown that\[\frac{P}{Q}=\frac{R}{S}\]. This is called the balancing condition. If any three resistances are known the fourth can be found. The practical form of wheatstone bridge is slide wire bridge or meter bridge. Using this the unknown resistance can be determined as \[S=\left( \frac{100-l}{l} \right)\times R\] where l is the balancing length of the Meter bridge.
In a wheatstone bridge circuit, \[P=5\Omega \], \[Q=6\Omega \], \[R=10\,\Omega \] and \[S=5\Omega \]. What is the value of additional resistance to be used in series with S, so that the bridge is balanced?
A)
\[9\,\Omega \] done
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B)
\[7\,\Omega \] done
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C)
\[10\,\Omega \] done
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D)
\[5\,\Omega \] done
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question_answer 37)
A wheatstone bridge consisting of four arms of resistances P, Q, R, S is most sensitive when :
A)
all the resistances are equal done
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B)
all the resistances are unequal done
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C)
the resistances P and Q are equal but R > > P and S > > Q done
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D)
the resistances P and Q are equal but R < < P and S < < Q. done
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question_answer 38)
When a metal conductor connected to left gap of a meter bridge is heated, the balancing point
A)
shifts towards right done
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B)
shifts towards left done
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C)
remains unchanged done
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D)
remains at zero done
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question_answer 39)
The percentage error in measuring resistance with a meter bridge can be minimized by adjusting the balancing point close to :
A)
0 done
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B)
20 cm done
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C)
50 cm done
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D)
80 cm done
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question_answer 40)
In a meter bridge experiment, the ratio of left gap resistance to right gap resistance is 2 : 3. The balance point from left is :
A)
20 cm done
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B)
50 cm done
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C)
40 cm done
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D)
60 cm done
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question_answer 41)
Directions : (41-45)
Potentiometer: An ideal Voltmeter
Potentiometer is an apparatus used for measuring the emf of a cell or potential difference between two points in an electrical circuit accurately. It is also used to determine the internal resistance of a primary cell. The potentiometer is based on the principle that, if V is the potential difference across any portion of the wire of length / and resistance R. then \[V\propto l\] or \[V=kl\] where k is the potential gradient. Thus, potential difference across any portion of potentiometer wire is directly proportional to length of the wire of that portion. The potentiometer wire must be uniform. The resistance of potentiometer wire should be high.
Which one of the following is true about potentiometer?
A)
Its sensitivity is low. done
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B)
It measures the emf of a cell very accurately done
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C)
It is based on deflection method done
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D)
None of these done
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question_answer 42)
A current of 1.0 mA is flowing through a potentiometer wire of length 4 cm and of resistance \[4\Omega \]. The potential gradient of the potentiometer wire is :
A)
\[{{10}^{-3}}\,V\,{{m}^{-1}}\] done
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B)
\[{{10}^{-5}}\,V\,{{m}^{-2}}\] done
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C)
\[2\times {{10}^{-3}}\,V\,{{m}^{-1}}\] done
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D)
\[4\times \,{{10}^{-3}}\,V\,{{m}^{-1}}\] done
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question_answer 43)
Sensitivity of a potentiometer can be increased by
A)
decreasing potential gradient along the wire done
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B)
increasing potential gradient along the wire done
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C)
decreasing current through the wire done
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D)
Increasing current through the wire done
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question_answer 44)
A potentiometer is an accurate and versatile device to make electrical measurements of EMF because the method involves
A)
potential gradients done
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B)
a condition of no current flow through the Galvanometer done
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C)
a combination of cells, galvanometer and resistances done
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D)
cells done
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question_answer 45)
In a potentiometer experiment, the balancing length is 8 m, when the two cells \[{{E}_{1}}\] and \[{{E}_{2}}\] are joined in series. When the two cells are connected in opposition the balancing length is 4 m. The ratio of the e.m.f of two cells \[\left( {{E}_{1}}/{{E}_{2}} \right)\] is :
A)
1 : 2 done
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B)
2 : 1 done
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C)
1 : 3 done
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D)
3 : 1 done
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question_answer 46)
Directions : (46-50) Heat Produced bt Electric current Whenever an electric current is passed through a conductor, it becomes hot after some time. The phenomenon of the production of heat in a resistor by the flow of an electric current through it is called heating effect of current or Joule heating. Thus, the electrical energy supplied by the source of emf is converted into heat. In purely resistive circuit, the energy expended by the source entirely appears as heat. But if the circuit has an active element like a motor, then a part of the energy supplied by the source goes to do useful work and the rest appears as heat. Joule's law of heating form the basis of various electrical appliances such as electric bulb, electric furnace, electric press etc.
Which of the following is a correct statement?
A)
Heat produced in a conductor is independent of the current flowing. done
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B)
Heat produced in a conductor varies inversely as the current flowing. done
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C)
Heat produced in a conductor varies directly as the square of the current flowing. done
clear
D)
Heat produced in a conductor varies inversely as the square of the current flowing. done
clear
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question_answer 47)
If the coil of a heater is cut to half, what would happen to heat produced?
A)
Doubled done
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B)
Halved done
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C)
Remains same done
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D)
Becomes four times done
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question_answer 48)
A 25 W and 100 W are joined in series and connected to the mains. Which bulbs will glow brighter?
A)
100 W done
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B)
25 W done
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C)
both bulbs will glow brighter done
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D)
none will glow brighter done
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question_answer 49)
A rigid container with thermally insulated wall contains a coil of resistance\[100\,\Omega \], carrying current 1A. Change in its internal energy after 5 min will be :
A)
0 kJ done
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B)
10 kJ done
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C)
20 kJ done
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D)
30 kJ done
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question_answer 50)
The heat emitted by a bulb of 100 W in 1 min is :
A)
100 J done
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B)
1000 J done
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C)
600 J done
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D)
6000 J done
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