JEE Physics - Current Electricity Chapter Sample Question Paper With Answer Key
Exam Duration: 60 Mins Total Questions : 50
In order to have maximum current from a battery in an external wire of resistance R, the cells must be an external wire of resistance R, the cells must be arranged in such a combination so that the internal resistance r of the battery is
- (a)
r = R if cells are connected in series
- (b)
r = R if cells are connected in parallel
- (c)
r = R if cells are arranged in series-parallel combination
- (d)
r < R if cells are arranged in series-parallel combination
On dipping a conducting rod in boiling water, its conducitivity
- (a)
increases
- (b)
decreases
- (c)
remains unchanged
- (d)
decreased for thin rod but increases for thick rod
A conducting wire of lenght 'l' and radius of cross- section 'a' has resistance 4 ohms. It is melted to form a wire of length 4l. Then resistance of new wire is
- (a)
4 ohm
- (b)
16 ohm
- (c)
1 ohm
- (d)
64 ohm
A uniform copper wire carries a current I ampere and has n carriers per \(metre^{3}\). The length of the wire is l metre and its area of cross-section a \(metre^{2}\). If the charge on a carrier is q coulombs, the drift velocity in \(ms^{-1}\) is given by
- (a)
\(naq\over l\)
- (b)
\(I\over naq\)
- (c)
\(Iln\over a\)
- (d)
\(I\over nalq\)
Tungsten wire obeys Ohm's law because
- (a)
the wire becomes hot when current flows
- (b)
the resistance is proportional to temperature
- (c)
the current is proportional to potential difference at constant temperature
- (d)
the current is proportional to the number of charge carriers
For making standard resistances such as 1.00 ohm, the material of the wire should best have a temperature coefficient of resistance which is
- (a)
low
- (b)
high
- (c)
negative
- (d)
zero
Electrical resistance can be
A. wire-bound resistance
B. carbon resistance
C. markedly with distance from the centre
D. decreases with distance from the centre
- (a)
A is correct
- (b)
A, B are correct
- (c)
A, C,D are correct
- (d)
A, B, C, D all are correct
In comparison to darbon resistances, the wattage of wire-wound resistance. In general, are
- (a)
higher
- (b)
lower
- (c)
comparable
- (d)
negligibly small
Conductivity increases in the order of
- (a)
silver, copper, aluminium, pure germanium
- (b)
pure germanium, aluminium, copper, silver
- (c)
pure germanium, copper, aluminium, silver
- (d)
copper, aluminium, silver, pure germanium
Instrument used to measure resistance is
- (a)
metre bridge
- (b)
voltmeter
- (c)
potentiometer
- (d)
electrometer
A uniform wire of resistance 4 ohm is cut into two equal lenghths. Each wire is drawn to twice its length. Resistance of each wire will be
- (a)
16 ohm
- (b)
2 ohm
- (c)
4 ohm
- (d)
8 ohm
What is the colour code of (100 \(^{+}_{-}\) 50%) ohm resistance ?
- (a)
Brown Yellow Red Gold
- (b)
Brown Orange Brown silver
- (c)
Brown Black Brown Gold
- (d)
Brown Brown Black Silver
The wire on a metre bridge is 100 cm long. For the most accurate measurement of an unknown resistance, the balance-point on the wire in cm should best be in the range
- (a)
0-20 cm
- (b)
20-40 cm
- (c)
40-60 cm
- (d)
60-80 cm
In a metre bridge experimeter, an unknown resistance P is compared with a known resistance Q. Then P should best be
- (a)
much lower in value than Q
- (b)
much higher in value than Q
- (c)
on the right of Q in the bridge circult
- (d)
the same order as Q
A metre bridge is connected across a battery of 2 volts and a resistance of 995 ohms. The potential drop per cm of the metre bridge wire is 0.1 mV. The resistance of wire is
- (a)
5 ohm
- (b)
10 ohm
- (c)
15 ohm
- (d)
20 ohm
The e.m.f of two cells may be compared using
- (a)
voltmeter
- (b)
voltameter
- (c)
potentiometer
- (d)
wheatstone bridge (or metre bridge)
A cube of side 10 cm has resistance of 50 ohm across two opposite faces. The electrical conductivity of its material in siements per metre is
- (a)
0.2
- (b)
\(2 \times 10^{-15}\)
- (c)
\(20 \times10^{-3}\)
- (d)
0.02
A wire of radius r and resistance R is drawn so that its length becomes n times the original length. The new resistance of the wire will be
- (a)
nR
- (b)
\(n^{2}R\)
- (c)
\(\sqrt n R\)
- (d)
2nR
The sensitivences of a potentiometer can be increased by
- (a)
increasing the e.m.f of the cell
- (b)
decreasing the length of the wire
- (c)
increasing the length of the wire
- (d)
decreasing the resistance connected in series with the cell
Choos ethe CORRECT statement
- (a)
Parallel grouping of cells is used for maximum current (or power) when the external resistance is small as compared to total internel resistance
- (b)
Series grouping of cells is used for maximum current (or power) when the external resistance is large as compared to total internal resistance
- (c)
Series-parallel grouping of cells is used for maximum current (or power) when
\(R_{s}>R>R_{p}\)
where R - external resistance
\(R_{s}\) = total internal resistance of parallel grouping of cells - (d)
All of the above
Choose CORRECT statement
- (a)
In the absence of an electric field, there will be no current in a conductor
- (b)
A moving coil galvanometer can be converted into an ammeter by using a low resistance in series
- (c)
A moving coil galvanometer can be converted into a voltmeter by using a high resistance in paralle
- (d)
All of the above
Which of the following is NOT a universal law ?
- (a)
Ohm's law
- (b)
Charge conservation
- (c)
Coulomb's law of electrostatic force
- (d)
Equation of continuity
The steady current flows in a metallic condutor of non-uniform cross- section. The quantity/quantities constant along the length of the conductor is/are
- (a)
current, electric field and drift velocity
- (b)
drift speed only
- (c)
current and drift speed
- (d)
current only
If there is an increase in length by 0.1% due to streching, the percentage increase in its resistance will be
- (a)
0.1%
- (b)
0.2%
- (c)
1%
- (d)
2%
At what temperature, the resisitance of a copper wire will become three times its value at \(0^{o}\) c ? (Temperature coefficient of resistance for copper = 4 \(\times 10^{-3}\) per \(^{o}C\))
- (a)
\(400^{o}C\)
- (b)
\(450^{o}C\)
- (c)
\(500^{o}C\)
- (d)
\(550^{o}C\)
A 2 \(\Omega\) resister is connected in series with R \(\Omega\) resistor. This combination is connected across a cell. When the potential difference across 2 \(\Omega\) resistor is balanced on a potentiometer wire, null point is obtained at a length of 300 m cm. When the same procedure is repeated for R \(\Omega\) resistor, null point is obtained at a length of 350 cm. Value of R is
- (a)
2.33 \(\Omega\)
- (b)
3.33 \(\Omega\)
- (c)
4.66 \(\Omega\)
- (d)
5 \(\Omega\)
Two cells of same e.m.f. E but of different internal resistance \(r_{1}\) and \(r_{2}\) are connected in series with an external resistance R. The potential drop across the first cell is found to be zero. The external resistance R is
- (a)
\(r_{1}\) + \(r_{2}\)
- (b)
\(r_{1}\) - \(r_{2}\)
- (c)
\(r_{2}\) - \(r_{1}\)
- (d)
\(r_{1}\)\(r_{2}\)
The masses of three wires of copper wire are in the ratio 1 : 3 : 5 and lengths are in the ratio 5 : 3 : 1. Then the ratio of their electrical resistances are
- (a)
1 : 3 : 5
- (b)
5 : 3 : 1
- (c)
1 : 15 : 25
- (d)
125 : 15 : 1
A carbon resistance has coloures strips as brown, green, orange and silver respectively. The resistance is
- (a)
15 K\(\Omega \ ^{+}_{-}\) 10%
- (b)
10 K\(\Omega \ ^{+}_{-}\) 10%
- (c)
15 K\(\Omega \ ^{+}_{-}\) 5%
- (d)
10 K\(\Omega \ ^{+}_{-}\) 10%
The terminal potential different of a battery exceed its e.m.f. when it is connected
- (a)
in parallel with a battery of higher e.m.f.
- (b)
in series with a battery of higher e.m.f.
- (c)
in series with a battery of lower e.m.f.
- (d)
in parallel with a battery of lower e.m.f.
The conductivity of superconductor is
- (a)
infinite
- (b)
very large
- (c)
very small
- (d)
zero
Two resistances \(R_{1}\) and \(R_{2}\) are made of different materials. The temperature coefficient of material of \(R_{1}\) is \(\alpha\) and that of material \(R_{2}\) is -\(\beta \). The resistance of series combination of \(R_{1}\) and \(R_{2}\) will not change with temperature if \(R_{1}\)/\(R_{2}\) equals
- (a)
\(\alpha \over \beta\)
- (b)
\(\alpha + \beta\over\alpha -\beta\)
- (c)
\(\alpha^{2}+\beta^{2}\over\alpha+\beta\)
- (d)
\(\beta\over\alpha\)
A wire of rasistance R and of radius r is drawn into another wire of radius 2r, the new resistance will be
- (a)
R/2
- (b)
R/16
- (c)
2R
- (d)
4R
Voltmeters \(V_{1}\) and \(V_{2}\) are connected in series across a DC line. \(V_{1}\) reads 80 V and has a per volt resistance of 200\(\Omega\). \(V_{2}\) has a total resistance of 32 K ohm. The line voltage is
- (a)
120V
- (b)
160V
- (c)
220V
- (d)
240V
If n, e, \(\tau \) and m represent electron density, charge, relaxation time and mass of an electron respectively, then the resistance of a wire of lenght l and cross-section A is
- (a)
\(2m3\over ne^{2}\tau A\)
- (b)
\(2m\tau A\over ne^{2}l\)
- (c)
\({ne^{2}\tau\over 2m}.{A\over l}\)
- (d)
\({ne^{2}m\over 2\tau}.{l\over a}\)
For which of the following dependence of drift velocity \(\vartheta _{d}\) on electric field E, is Ohm's law obeyed?
- (a)
\(\vartheta _{d} \propto E^{2}\)
- (b)
\(\vartheta _{d} \propto E^{1/2}\)
- (c)
\(\vartheta _{d} \propto E\)
- (d)
\(\vartheta _{d} \propto E^{0}\)
The dimensions of electrical conductivity are
- (a)
\(M^{-1}L^{-3}T^{-3}A\)
- (b)
\(M^{-1}L^{-3}T^{-3}A^{2}\)
- (c)
\(ML^{-3}T^{3}A^{-2}\)
- (d)
\(M^{0}L^{0}T^{0}A^{0}\)
All the edges of a block with parallel faces are unequal. Its tangent edge is twice its shortest edge. The ratio of the maximum to minimum resistance between parallel faces is
- (a)
8
- (b)
4
- (c)
2
- (d)
None of these
Two wires of resistance R1 and R2 have temperature coefficient of resistance \(\alpha_1 \ and \ \alpha_2\) respectively. These are joined in series. The effective temperature coefficient of resistance is
- (a)
\(\alpha_1+\alpha_2\over2\)
- (b)
\(\sqrt{\alpha_1+\alpha_2}\)
- (c)
\(\alpha_1R_1+\alpha_2R_2\over R_1+R_2\)
- (d)
\(\sqrt{R_1R_2\alpha_1\alpha_2}\over\sqrt{R^2_1+R^2_2}\)
The temperature coefficient of a resistance wire is 0.00125 per degree. The resistance at 300 k is 1\(\Omega\). At what temperature its resistance will be 2\(\Omega\)?
- (a)
1154K
- (b)
1100K
- (c)
600K
- (d)
1400K
A fuse wire with a radius of 1mm blows at 1.5A. If the fuse wire of the same material should blow at 3.0A. The radius of the wire must be
- (a)
2mm
- (b)
\(\sqrt2\)mm
- (c)
0.5mm
- (d)
8.0mm
Two identical fuses are rated at 10A. If they are joined
- (a)
in series, the combination acts as a fuse of rating 20A
- (b)
in parallel, the combination acts as a fuse of rating 5A
- (c)
in series, the combination acts as a fuse of rating 10A
- (d)
in series, the combination acts as a use of rating 6A
A wire when connected to 220V mains supply has power dissipation P1. Now, the wire is cut into two equal pieces which are connected in parallel to same supply. Power dissipation in this case is P2. Then P1:P2 is
- (a)
1
- (b)
2
- (c)
3
- (d)
4
The same mass of copper is drawn into two wires 2mm and 3mm thick. The two wires are connected in series and current is passed through them. The ratio of heat produced in the two wires is
- (a)
\(9\over 4\)
- (b)
\(3\over 2\)
- (c)
\(2\over 3\)
- (d)
\(81\over 16\)
In a large building, there are 15 bulbs of 40W, 5 bulbs of 100W, 5 fans of 80W and 1 heater of 1kW. The voltage of the electric mains is 220V. The minimum capacity of the main fuse of the building will be
- (a)
8A
- (b)
10A
- (c)
12A
- (d)
14A
Two electric bulbs marked 25W-220V and 100W-220V are connected in series to a 440V supply. Which of the bulbs will fuse?
- (a)
Both
- (b)
100W
- (c)
25W
- (d)
Neither
Resistance of a given wire is obtained by measuring the current flowing in it and the voltage difference applied across it. If the percentage errors in the measurement of the current and the voltage difference are 3% each, then error in the value of resistance of the wire is
- (a)
6%
- (b)
zero
- (c)
1%
- (d)
3%
I a wire is stretched to make it 0.1% longer, its resistance will
- (a)
increase by 0.2%
- (b)
decrease by 0.2%
- (c)
decrease by 0.05%
- (d)
increase by 0.05%
If 400\(\Omega\) of resistance is made by adding four 100\(\Omega\) resistance of tolerance 5%, then the tolerance of the combination is
- (a)
20%
- (b)
5%
- (c)
10%
- (d)
15%
The current in the primary circuit of a potentiometer is 0.2A. The specific resistance and cross-section of the potentiometer wire are 4X10-7\(\Omega -m\) and 8X10-7m2 respectively. The potential gradient will be equal to
- (a)
0.2 V/m
- (b)
1 V/m
- (c)
0.3 V/m
- (d)
0.1 V/m
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