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 electrochemical equivalent of a material in an electrolyte depends on
- (a)
the amount of material present in electrolyte
- (b)
the amount of charge passed through electrolyte
- (c)
the current through the electrolyte
- (d)
the nature of the material of electrolyte
Two heater wires of equal length are first connected in series and then in parallel. The ratio of heat produced in two cases is
- (a)
2:1
- (b)
1:2
- (c)
4:1
- (d)
1:4
A certain charge liberates 1.6 g of oxygen. The same charge will liberate how many grans of silver:
- (a)
1.6g
- (b)
2.16g
- (c)
10.8g
- (d)
21.6g
An ammeter connected in series with a silver. Voltmeter reads 0.810 A. If the weight of silver deposited in 20 minutes is 1.071 g, the error in the reading of ammeter is (Electro-chemical equivalent of silver is 1.118 X 10-3 gC-1)
- (a)
+0.12 A
- (b)
+0.012 A
- (c)
-0.012 A
- (d)
-0.12 A
A resistor R1 dissipates the power P when connected to a certain source of e.m.f. If a resistor R2 is put in series with R1, the power dissipated by R1
- (a)
increases
- (b)
decreases
- (c)
remains the same
- (d)
either increases or decreases depending on the relative values of R1 and R2.
For a given temperature difference which of the following pairs will generate maximum thermo e.m.f?
- (a)
Silver-gold
- (b)
Iron copper
- (c)
Lead-nickel
- (d)
Antimony-bismuth
In a thermocouple, the thermo e.m.f. is of the order of
- (a)
microvolt
- (b)
millivolt
- (c)
one volt
- (d)
a fraction of one volt
For a thermocouple the netural temperature is 2700C when its cold junction is at 200C. What will be the neutral temperature and the temperature of inversion when the temperature of cold junction is increased to 400C?
- (a)
2900C, 5800C
- (b)
2700C, 5800C
- (c)
2700C, 5000C
- (d)
2900C, 5400C
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
The e.m.f. in a thermocouple one junction of which is kept at 00C, is given by E=at+bt2. The peltier coefficient is
- (a)
(a + 2 bt)t
- (b)
[a + 2b(t-273)]t
- (c)
(a + 2bt)(t + 273)
- (d)
NONE OF THE ABOVE
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
The temperature of the cold junction of a thermocouple is 00C and the temperature of hot junction is T0C. The e.m.f. is E = 16T-0.04 T2(\(\mu \)V). The inversion temperature Ti is
- (a)
2000C
- (b)
4000C
- (c)
1000C
- (d)
3000C
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)
\(S=\frac { { \pi }^{ } }{ { T }^{ 2 } } \)
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
Which of the following statements is correct?
- (a)
Both Peltier and Joule effects are reversible
- (b)
Both Peltier and Joule effects are reversible
- (c)
Joule effect is reversible, whereas Peltier effect is irreversible
- (d)
Joule effect is irreversible, whereas Peltier effect is reversible
When two equal resistances are connected in parallel to the plates of a cell of negligible internal resistance, the power developed is \(\rho \), when the same resistances are connected in series across the same cell, the power developed is
- (a)
\(\rho \)/4
- (b)
\(\rho \)/2
- (c)
\(\rho \)
- (d)
4\(\rho \)
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
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