IISER Physics - Current Electricity
Exam Duration: 45 Mins Total Questions : 30
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
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
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
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
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
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 \(\Omega\)
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
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
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)
\(\vartheta _{d} \propto E^{0}\)
Which property of free electrons causes increase in the resistance of a conductor with rise in temperature?
- (a)
number density
- (b)
Relaxation time
- (c)
Mass
- (d)
None of the above
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
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
An electric heater rated as (500W and 200V) varies the temperature of 1 kg water from 15oC to its boiling point in 15 min. The heat efficiency of the heater is
- (a)
79%
- (b)
97%
- (c)
69%
- (d)
96%
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%