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
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
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 e.m.f of two cells may be compared using
- (a)
voltmeter
- (b)
voltameter
- (c)
potentiometer
- (d)
wheatstone bridge (or metre bridge)
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
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
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)
\({ne^{2}m\over 2\tau}.{l\over a}\)
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\(\Omega\)
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)
\(\sqrt{R_1R_2\alpha_1\alpha_2}\over\sqrt{R^2_1+R^2_2}\)
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