IISER Physics - Thermal and Chemical Effects of Currents
Exam Duration: 45 Mins Total Questions : 30
How long will it take a current of 50A to produce 32g of oxygen by the electrolysis of water? Oxygen has an atomic mass of 16 and a valence of 2.
- (a)
7720 s
- (b)
30880 s
- (c)
15440 s
- (d)
NONE OF THESE
When 1 gram of water is formed by the combination of hydrogen and oxygen, 3800 calories of heat are evolved. Minimum voltage required to decompose 9 gram of water is
- (a)
1.67 volt
- (b)
2.22 voit
- (c)
1.49 volt
- (d)
9.00 volt
The heat produced in a conductor is
- (a)
independent of resistivity \(\rho \) of matereial of conductor
- (b)
proportional to \(\rho \)
- (c)
inversely proportional to \(\rho \)
- (d)
proportional to \(\sqrt { \rho } \)
The volume of hydrogen liberated at N.T.P. by the charge which liberates 0.3177g of copper. (Atomic weight = 63.546) is
- (a)
224 cc
- (b)
112 cc
- (c)
56 cc
- (d)
NONE OF THESE
In an electrolysis experiment a current I passes through two different cells in series, one containing a solution of CuSO4 and the other a solution of AgNO3. The rate of increase of teh weights of the cathodes in the two cells will be
- (a)
in the ratio of the densities of Cu and Ag
- (b)
in the ratio of atomic weights of Cu and Ag
- (c)
in the ratio of half the atomic weight of Cu to half the atomic weight of Ag
- (d)
in the ratio of half the atomic weight of Cu to the atomic weight of Ag
Thomson coefficient for lead is
- (a)
zero
- (b)
negative
- (c)
positive but less than one
- (d)
positive but greater than one
In a copper voltameter experiment current is decreased to one-fourth of teh initial value but it is passed for four times the earlier duration. The amount of copper deposited will be
- (a)
same
- (b)
one-fourth the previous value
- (c)
four-times the previous value
- (d)
one-sixth of the previous value
Choose INCORRECT statement
- (a)
Seebeck effect may be used as a thermoelectric generator
- (b)
Peltier effect may be used as a thermoelectric referigerator
- (c)
Thermopile is used to measure heat radiations
- (d)
Thermopile is used to detect heat radiations
Of the following the one that does not make use of chemical effect of electric current is
- (a)
electrotyping
- (b)
extraction of metals from ores
- (c)
voltaic cell
- (d)
thermostat
Of the following the one that does not make use of thermoelectric effect is
- (a)
thermoelectric generator
- (b)
thermoelectric thermometer
- (c)
thermopile
- (d)
thermograph
At the temperature of inversion, thermoelectric current
- (a)
flows from copper to iron through hot junctiion
- (b)
flows from iron to copper through hot junction
- (c)
is maximum
- (d)
does not depend on the temperature of cold junction
The e.m.f. in a thermocouple one junction of which is kept at 00C, is given by E = at + bt2. The value of the Thomson coefficient is
- (a)
2at
- (b)
2bt
- (c)
2b (t + 273)
- (d)
bt
Specific heat of electricity can be defined by which one of the following:
- (a)
Peltier's coefficient
- (b)
Thomson's coefficient
- (c)
Seeback's coefficient
- (d)
Joule's coefficient
If a current is passed in thermocouple formed of two dissimilar metals, one junction is heated and other is cooled. If \({ \pi }_{ 1 }\) and \({ \pi }_{2 }\) are the Peltier coefficients of cold and hot junctions, then the net e.m.f. across the junction is
- (a)
\(1/2{ { {( { \pi }_{ 1} }^{ }+\pi }_{ 2 } }^{ })\)
- (b)
\({ { { { \pi }_{ 2 } }^{ }-\pi }_{ 1 } }^{ }\)
- (c)
\({ { { { \pi }_{ 2 } }^{ 2 }-\pi }_{ 1 } }^{ 2 }\)
- (d)
\(\sqrt { { \pi }_{ 1 }{ \pi }_{ 2 } } \)
The relation between Seeback coefficient (or thermoelectric power) S and Peltier coefficient \(\pi \) is given by
- (a)
S = \(\pi \)T
- (b)
\(S=\frac { { \pi }^{ } }{ { T }^{ } } \)
- (c)
\(S=\frac { { \pi }^{ 2 } }{ { T }^{ } } \)
- (d)
\(S=\frac { { \pi }^{ } }{ { T }^{ 2 } } \)
The cause of heat production in a current carrying conductor is
- (a)
collisio of free electrons with one another
- (b)
high drift speed of free electrons
- (c)
collisions of free electrons with atoms or ions of the conductor
- (d)
high resistance value
Three electric bulbs of 40W, 60W and 100W use the tungsten wire of the same diameter. Which bulb uses longer wire?
- (a)
60W
- (b)
100W
- (c)
40W
- (d)
All use the same length
If the electric current in a lamp decreases by 5%, then the power output decreases by
- (a)
20%
- (b)
10%
- (c)
5%
- (d)
2.5%
Two resistances R1 and R2 when connected in series consume, power equal to 25 W. When connected in parallel they consume 100 W. What is the ratio of power of each?
- (a)
1/4
- (b)
1/3
- (c)
1/2
- (d)
1
In a D.C. circuit, the power dissipated per unit volume is directly proportional to
- (a)
current
- (b)
electric field
- (c)
resistivity
- (d)
square of electric field
A 50C rise in temperature is observed in a conductor by passing a current. When the current is doubled, the rise in temperature will be nearly
- (a)
100C
- (b)
160C
- (c)
200C
- (d)
120C
The maximum current that flows through a fuse wire, before it blows out, varies with its radius r as
- (a)
r1/2
- (b)
r2/3
- (c)
r
- (d)
r3/2
When a copper voltameter is connected with a battery of e.m.f. 12V, 2 g of copper is deposited in 30 minutes. If the same voltameter is connected across a 6V battery, the mass of copper deposited in 45 minutes would be
- (a)
1g
- (b)
1.5g
- (c)
2g
- (d)
2.5g
If a cell of constant electromotive force produces the same amount of heat during the same time in two independent resistance R1 and R2, when connected seperately one after the other, across the cell, then the internal resistance of the cell is
- (a)
(R1+R2)
- (b)
(R1-R2)/2
- (c)
\(\sqrt { { R }_{ 1 }{ R }_{ 2 }/2 } \)
- (d)
\(\sqrt { { R }_{ 1 }{ R }_{ 2 } } \)
A current passing through a copper voltameter deposits 0.002 kg of copper on cathode plate in 100 minutes. If there are 1025 coper atoms in one kg of copper, the electric charge delivered to cathode by Cu++ ions per second will be
- (a)
0.53 C
- (b)
0.71 C
- (c)
1.06 C
- (d)
10.06 C
A 25W, 220V bulb and another 100W,220V bulb are connected in series. This arrangement is then connected to the mains. Which bulb will glow brighter?
- (a)
25W
- (b)
100W
- (c)
first 25W and then 100W
- (d)
both with same brightness
If two bulbs of wattage 25 and 30 W, each rated at 220 volts are connected in series with a 440 volt supply, which bulb will fuse?
- (a)
25W bulb
- (b)
30 W bulb
- (c)
neither of them
- (d)
both of them
In electrolysis, the amount of mass deposited or liberated at an electrode is directly proportional to
- (a)
amount of charge
- (b)
square of current
- (c)
concentration of electrolyte
- (d)
square of electric charge
An electric kettle has two heating elements. One brings it to boil in ten minutes and the other in fifteen minutes. If two heating filaments are connected in parallel, the water in kettle will boil in
- (a)
6 minutes
- (b)
8 minutes
- (c)
25 minutes
- (d)
5 minutes
A wire of length L and 3 identical cells of negligible internal resistances are connected in series. Due to the current, the temperature of the wire is raised by \(\Delta \)T in a time t. A number N of similar cells is now connected in series with a wire of the same material and gross-section but of length 2L. The temperature of the wire is raised by the same amount \(\Delta \)T in the same time t. Then value of N is
- (a)
4
- (b)
6
- (c)
8
- (d)
9