Blackbody

Q.

If temperature of a black body increases from $7^{\circ }Cto{287}^{\circ }$ , then the rate of energy radiation increases by

1. 

2. 16

3. 4

4. 2

Q. if radius of spherical ball is measured as ⊂5.2+0.2⊃ cm then percentage error in the calculation of volume of ball is

Q. A uniform spherical ball is moving with terminal velocity inside a liquid. The rate of heat loss varies with the radius (r) of the ball as Options: a- r b-r^2 c- r^4 d-r^4

Q. It takes 20 min to melt 10 g of ice, when rays from the sun are focussed by a lens of diameter 5 cm on a block ofice. If the latent heat for ice is 80 cal/g, the heat received per unit area per unit time at the surface of earth(in cal cm-2 min-1) is(1) 2.04(3) 0.204(2) 3.04(4) 204

Q. 1 kcal per hour of heat flowing through a rod ofiron. When the rod is cut down to 4 pieces then what will be the heat flowing through each piecehaving same diferential temperature?

Q. A refrigerator based on carnots cycle receives heat from 227^° c and rejects heat at 727^° c . let work required per unit heat received be x . if the same machine is used as carnots engine then its efficiency is y . then ratio of x and y is

Q.

A black body is at a temperature of 2880 K. The

energy of radiation emitted by this object with

wavelength between 499 nm and 500 nm is $U_1$,

between 999 nm and 1000 nm is $U_2$ and between

1499 nm and 1500 nm is $U_3$. The Wein's constant

b = 2.88 x ${10}^6$ nm K. Then

1. U₁>U₂

2. U₂>U₁

3. U₁=0

4. U₃=0

Q. Two diagonally opposite corners of a square made ofa four thin rods of same material, same dimensionsare at temperature 40^° C and 10^° C. If only heat conduction takes place, then the temperature difference between other two corners will be(1) 10^° C(2) 15^° C(3) 25^° C (4)0^0

Q. If the temperature of the body is increases from 27 degree C to 327 degree C the wavelength becomes

Q.

A black body at 200 K is found to exit maximum energy at a wavelength of 14 $\mu$ m. When its temperature is raised to 1000K, the wavelength at which maximum energy is emitted is

1. 14 μm

2. 70 μF

3. 2.8 μm

4. 2.04 mm

Q. An ideal black body at room temperature is thrown into a furnace. It is observed that

1. initially it is the darkest body and at later times the brightest
2. it is the darkest body at all times
3. it cannot be distinguished at a times
4. initially it is the darkest body and at later times it cannot be distinguished

Q. HEAT: Multi Correct: Two spheres A and B having radii rA and rB where rB =2rA emit radiations with peak intensities at wave lengths 400 nm and 800 nm respectively. If their temperature are TA and TB respectively in Kelvin scale, their emissive powers are EA and EB and energies emitted per second are PA and PB then A. TA / TB = 2 B. PA / PB = 4 C. EA / EB = 8 D. EA / EB = 4

Q. A black body of temperature T is inside a chamber of temperature $T_0$. Now the closed chamber is slightly opened to sun such that temperature of black body (T) and chamber $\left(T_0\right)$ remains constant

1. black body will absorb more radiation
2. black body will absorb less radiation
3. black body emit more energy
4. black body emit energy equal to energy absorbed by it

Q. The spectrum from a black body radiation is a

1. Line spectrum
2. Band spectrum
3. Continuous spectrum
4. Line and band spectrum both

Q. A heated body emits radiation which has maximum intensity near the frequency f_0 .The emissivity of the material is 0.5, if absolute temperature of the body is doubled, then maximum intensity of radiation will have the frequency ?

Q.

The wavelength of maximum energy released during an atomic explosion was $2.93\times {10}^{-10}m$. Given that Weins constant is $2.93\times {10}^{-3}{m}^{-K}$, the maximum temperature attained must be of the order of

1. 

2. 

3. 

4. 

Q. A solid iron sphere of density ρ, emissivity e, and specific heat C has radius R. If it is heated to temperature 400 K and suspended inside a chamber whose walls are almost 0 K, then what is the time required for the temperature of the sphere to drop to 200 K?

Q. A black body at a temperature of ${327}^{\circ }\text{C}$ radiates $4{\text{cal cm}}^{-2}{\text{s}}^{-1}$ heat per unit area per unit time. At a temperature of ${927}^{\circ }\text{C}$, the rate of heat radiated per unit area per unit time in ${\text{cal cm}}^{-2}{\text{s}}^{-1}$ will be

1. $16$
2. $32$
3. $64$
4. $128$

Q. 18 36 ML OF PURE WATER TAKE 100 SEC TO EVAPORATE FROM VESSEL AND HEATER CONNECTED TO AN ELECTRIC SOURCE DELIVER 806 WATT HEAT OF VAPOURISATION OF WATER IS

Q.

Explain why : (a) a body with large reflectivity is a poor emitter (b) a brass tumbler feels much colder than a wooden tray on a chilly day (c) an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace (d) the earth without its atmosphere would be inhospitably cold (e) heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water

Q. 2 solid spheres A and B made of same material have radii r and R respectively. both the spheres are cooled from the same temperature under conditions valid for newtons law of cooling . the rate of change in temperature is

Q. The plots of intensity vs wavelength for two black bodies having same area at temperatures $T_1$ and $T_2$ such that $T_2=2T_1$ is shown in the figure. Let the energy radiated per second by body 1 and body 2 be $E_1$ and $E_2$ respectively. Pick the correct statement.

1. $E_1=16E_2$
2. $E_2=16E_1$
3. $E_2=4E_1$
4. None of the above

Q. A black body radiates heat energy at the rate of $2\times {10}^5{\text{J-s}}^{-1}{\text{m}}^{-2}$ at a temperature of ${127}^{\circ }\text{C}$. The temperature of black body, at which the rate of heat radiation is $32\times {10}^5{\text{J-s}}^{-1}{\text{m}}^{-2}$ is

1. ${273}^{\circ }\text{C}$
2. ${527}^{\circ }\text{C}$
3. ${873}^{\circ }\text{C}$
4. ${927}^{\circ }\text{C}$