Q1
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
If $10^{6}$ electrons/s are flowing through an area of cross section of $10^{-4}$ m $^{2}$ then the current will be :-
A.
$1.6 \times 10^{-7}$ A
B.
$1.6 \times 10^{-13}$ A
C.
$1 \times 10^{-6}$ A
D.
$1 \times 10^{2}$ A
Q2
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
The current in a conductor varies with time t as $I = 2t + 3t^{2}$ A where I is amperes and t in seconds. Electric charge flowing through a section of the conductor during t = 2 s to t = 3 s is :-
A.
10 C
B.
24 C
C.
33 C
D.
44 C
Q3
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
10,000 electrons are passing per minute through a tube of radius $1\mathrm{cm}$ . The resulting current is:
A.
$10000\mathrm{A}$
B.
$0.25 \times 10^{-16}\mathrm{A}$
C.
$10^{-9}\mathrm{A}$
D.
$0.5 \times 10^{-19}\mathrm{A}$
Q4
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
There are $8.4 \times 10^{22}$ free electrons per cm $^{3}$ in copper. The current in the wire is 0.21 A (e = $1.6 \times 10^{-19}$ C). Then the drifts velocity of electrons in a copper wire of 1 mm $^{2}$ cross section, will be :-
A.
$2.12 \times 10^{-5}$ m/s
B.
$0.78 \times 10^{-5}$ m/s
C.
$1.56 \times 10^{-5}$ m/s
D.
none of these
Q5
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
There is a current of 40 amperes in a wire of $10^{-6}\mathrm{m}^2$ area of cross-section. If the number of free electrons per $\mathrm{m}^3$ is $10^{29}$ , then the drift velocity will be
A.
$1.25\times 10^{3}\mathrm{m / s}$
B.
$2.50\times 10^{-3}\mathrm{m / s}$
C.
$25.0\times 10^{-3}\mathrm{m / s}$
D.
$250\times 10^{-3}\mathrm{m / s}$
Q6
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
S.I. unit of current is :-
A.
C
B.
A
C.
A/s
D.
N/s
Q7
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
When no current flows through a conductor:
A.
the free electrons do not move
B.
the average speed of a free electron over a large period of time is zero
C.
the average velocity of a free electron over a large period of time is zero
D.
the average of square of velocities of all the free electrons at an instant is zero
Q8
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
The number of free electrons per 10 mm of an ordinary copper wire is about $2 \times 10^{21}$ . The average drift speed of the electrons is 0.25 mm/s. The current flowing is:-
A.
0.8 A
B.
8 A
C.
80 A
D.
5 A
Q9
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
In a Neon discharge tube $2.9 \times 10^{18}$ Ne $^{+}$ ions move to the right each second, while $1.2 \times 10^{18}$ electrons move to the left per second; electron charge is $1.6 \times 10^{-19}$ C. The current in the discharge tube is :-
A.
1 A towards right
B.
0.66 A towards right
C.
0.66 A towards left
D.
zero
Q10
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
Two wires each of radius of cross section r but of different materials are connected together end to end (in series). If the densities of charge carriers in the two wires are in the ratio 1:4, the drift velocity of electrons in the two wires will be in the ratio:
A.
1 : 2
B.
2 : 1
C.
4 : 1
D.
1 : 4
Q11
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
A current I flows through a uniform wire of diameter d when the electron drift velocity is v. The same current will flow through a wire of diameter d/2 made of the same material if the drift velocity of the electrons is
A.
v/4
B.
v/2
C.
2v
D.
4v
Q12
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
A wire has a non-uniform cross-section as shown in figure. A steady current flows through it. The drift speed of electrons at points P and Q is $v_{P}$ and $v_{Q}$ , then :-
A.
$\mathrm{v_P} = \mathrm{v_Q}$
B.
$\mathrm{v_P} < \mathrm{v_Q}$
C.
$\mathrm{V_P > V_Q}$
D.
data is insufficient
Q13
Allen
1. ELECTRIC CURRENT & DRIFT VELOCITY
MCQ
The plot represents the flow of current through a wire for different time intervals. The ratio of charges flowing through the wire corresponding to these time intervals is (see figure) :-
A.
2 : 1 : 2
B.
1 : 3 : 3
C.
1 : 1 : 1
D.
2 : 3 : 4
Q14
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
Three copper wires are there with lengths and cross-sectional areas as $(\ell, A)$ ; $\left(2\ell, \frac{A}{2}\right)$ and $\left(\frac{\ell}{2}, 2A\right)$ . Resistance:
A.
minimum for the wire of cross-sectional are $\frac{A}{2}$
B.
minimum for the wire of cross-sectional are $A$
C.
minimum for the wire of cross-sectional area $2A$
D.
same for all the three cases.
Q15
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
A wire of uniform cross-section A, length ℓ and resistance R is bent into a complete circle; the resistance between any two of diametrically opposite points will be:-
A.
$\frac{R}{2}$
B.
$\frac{R}{4}$
C.
$\frac{R}{8}$
D.
4R
Q16
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
The electric resistance of a certain wire of iron is R. If its length and radius both are doubled, then:-
A.
the resistance will be halved and the specific resistance will remain unchanged
B.
the resistance will be halved and the specific resistance will be doubled
C.
the resistance and the specific resistance, will both remain unchanged
D.
the resistance will be doubled and the specific resistance will be halved.
Q17
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
When a piece of aluminium wire of finite length is drawn to reduce its diameter to half its original value, its resistance will become :
A.
two times
B.
four times
C.
eight times
D.
sixteen times
Q18
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
As the temperature of a metallic resistor is increased, the product of resistivity and conductivity :-
A.
increases
B.
decreases
C.
may increase or decrease
D.
remains constant.
Q19
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
If a wire is stretched, so that its length is 20% more than its initial length, the percentage increase in the resistance of the wire is :-
A.
40%
B.
10%
C.
44%
D.
25%
Q20
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter the change in the resistance of the wire will be:-
A.
300%
B.
200%
C.
100%
D.
50%
Q21
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
On increasing the temperature, the specific resistance of a conductor and a semiconductor-
A.
both increase
B.
both decrease
C.
increases and decreases respectively
D.
decreases and increases respectively
Q22
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
A conductor with rectangular cross section has dimensions $(a \times 2a \times 4a)$ as shown in figure. Resistance across AB is x, across CD is y and across EF is z. Then
A.
$x = y = z$
B.
$x > y > z$
C.
$y > x > z$
D.
$x > z > y$
Q23
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
Specific resistance of a conductor increases with:-
A.
increase in temperature.
B.
increase in cross-sectional area
C.
increase in cross-sectional area and decrease in length.
D.
decrease in cross-sectional area.
Q24
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
The temperature coefficient of resistance of a wire is 0.00125 per degree celcius. At 300 K its resistance is 1 ohm. The resistance of the wire will be 2 ohms at a temperature:-
A.
1154 K
B.
1127 K
C.
600 K
D.
1400 K
Q25
Allen
2. OHM'S LAW & ELECTRICAL RESISTANCE
MCQ
The current voltage graph for a given metallic conductor at two different temperatures $T_{1}$ and $T_{2}$ are as shown in the figure. Then :-
A.
$\mathrm{T}_{1} > \mathrm{T}_{2}$
B.
$\mathrm{T}_{1} = \mathrm{T}_{2}$
C.
nothing can be said about $\mathrm{T}_{1}$ and $\mathrm{T}_{2}$
D.
$\mathrm{T}_{1} < \mathrm{T}_{2}$