The temperature of the black body increases from T to 2T. The factor by which the rate of emission will increase, is?
4
2
16
8
Two rods of same material have same length and area. The heat ΔQ flows through them for 12 minutes when they are joint side by side. If now both the rods are joined in parallel, then the same amount of heat ΔQ will flow in :
24 min
3 min
12 min
6 min
Which of the following circular rods, (given radius r and length l) each made of the same material and whose ends are maintained at the same temperature will conduct most heat?
r = 2ro, l = 2lo
r = 2ro, l = lo
r = ro, l = lo
r = ro, l = lo
The temperature of inversion of a thermocouple is 620°C and the neutral temperature is 300oC, what is the temperature of cold junction?
20o C
320o C
-20o C
40o C
Mercury boils at 367oC. However, mercury thermometers are made such that they can measure temperature upto 500oC. This is done by
maintaining vacuum above mercury column in the stem of the thermometer
filling nitrogen gas at high pressure above the mercury column
filling oxygen gas at high pressure above the mercury column
filling nitrogen gas at low pressure above the mercury column
Which of the following circular rods, (given radius r and length l) each made of the same material and whose ends are maintained at the same temperature will conduct most heat?
r = 2ro ; l = 2 lo
r = 2ro ; l = lo
r = ro ; l = lo
r = ro ; l = lo
Consider a compound slab consisting of two different materials having equal lengths, thicknesses and thermal conductivities K and 2K respectively. The equivalent thermal conductivity of the slab is
3 K
A black body has a wavelength of A at temperature 2000 K. Its corresponding wavelength at temperature 3000 K will be
The temperature of the sun can be found out by using
Wien's displacement law
Kepler's law of motion
Stefan's Boltzmann law
Planck's law
The thermo emf of a hypothetical thermocouple varies with the temperature θ of hot junction as E = in volts, where the ratio is 700o C. If the cold junction is kept at 0o C, then the neutral temperature is
700o C
1400o C
390o C
no neutral temperature is possible for this thermocouple
D.
no neutral temperature is possible for this thermocouple
When two wires composed of dissimilar metals are joined at both ends and one of the ends is heated, there is a continuous current which flows in the thermoelectric circuit.
The emf set in the thermocouple, when its two junctions are kept at different temperatures is called thermo e.m.f
Given:-
E = aθ + bθ2
=
P = a + 2 bθ
At θ = Tn ,P = 0
⇒ 0 = a + 2 b T
⇒ Tn =
⇒ Tn = -
Tn = - 350o C
The temperature of the hot junction of a thermocouple at which the elctromotive force on the thermocouple attains its maximum value, when the cold junction is maintained at constant temperature of 0o C , called neutral temperature.
But neutral temperature can never be negative ( less than zero)