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
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
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
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 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
Students (A, B, C) balance a Wheatstone bridge for measuring an unknown resistance 'A' uses ratio arm R=R,; 'B' uses \(R_{1} \ = \ 10 \ R_{2}\) and 'C' uses \(R_{1} \ = \ 100 \ R_{2}.\) Whose bridge is most sensitive?
- (a)
A's only
- (b)
A's and B's only
- (c)
C's only
- (d)
B's and C's only
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
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%
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 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
The resistance of a 10m long wire is 10\(\Omega\) . Its length is increased by 25% by stretching the wire uniformly. The resistance of wire will change to (approximately)
- (a)
12.5\(\Omega\)
- (b)
14.5\(\Omega\)
- (c)
15.6\(\Omega\)
- (d)
16.6\(\Omega\)
In a potentiometer experiment, the emf of a battery in the primary circuit is 20V and its internal resistance is 5\(\Omega\). There is a resistance box in series with the battery and the potentiometer wire, whose resistance can be varied from 120\(\Omega\) to 170\(\Omega\). Resistance of the potentiometer wire is 75\(\Omega\). The following potential differences cannot be measured using this potentiometer
- (a)
5V
- (b)
6V
- (c)
7V
- (d)
8V
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