JEE Main Physics - Thermal and Chemical Effects of Currents
Exam Duration: 60 Mins Total Questions : 30
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 \(\sqrt { \rho } \)
Gases begin to conduct electricity at low pressure because
- (a)
gases turn to plasma
- (b)
mean free path increases
- (c)
temperature decreases
- (d)
electrons in atoms can move freely at low pressure
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
Thermopile is an instrument
A. for detecting and measuring infrared radiations.
B. in which a number of thermocouples are connected in series.
C. in which a number of thermocouples are connected in parallel.
D. in which a number of thermocouples are either connected in series or parallel.
- (a)
if A is correct only
- (b)
if A and B are correct only
- (c)
if A and D are correct only
- (d)
if D is correct only
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
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
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
Peltier coefficient for the junction of a pair of metals is proportional to
- (a)
T
- (b)
\(\sqrt { T } \)
- (c)
T2
- (d)
1/T
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
If the potential difference across a conductor of specific resistance \(\rho \) remains constant then heat produced is directly proportional to
- (a)
\(\rho \)
- (b)
\({ \rho }^{ 2 }\)
- (c)
1/\(\rho \)
- (d)
\(\sqrt { \rho } \)
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
If a wire of resistance 20\(\Omega \) is covered with ice and a voltage of 210 V applied across the ends of the resistance wire, then rate of melting of ice is
- (a)
0.97 g/s
- (b)
6.7 g/s
- (c)
2 g/s
- (d)
NONE OF THESE
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
If J is the current density, then the power transferred per unit volume in joules in a resistivity \(\rho \) is
- (a)
J2/\(\rho \)
- (b)
J2\(\rho \)
- (c)
\(\rho \)J
- (d)
\(\rho \)2J2
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
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\(\rho \)
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
The smallest temperature difference that can be measured with a combination of a thermocouple of thermo e.m.f. 30 \(\mu \)V per degree and a galvanometer of 50 \(\Omega \) resistance, capable of measuring a minimum current of 3 X 10-7A is
- (a)
0.5 degree
- (b)
1.0 degree
- (c)
1.5 degree
- (d)
2.0 degree
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
A short-circuit coil is placed in a time varying magnetic field. Electrical power is dissipated due to the current induced in the coil. If the number of turns were to be quadrupled and the wire-radius halved, the electrical power dissipated would be
- (a)
halved
- (b)
the same
- (c)
doubled
- (d)
quadrupled