Which of the following statements is wrong ?

(a) Rough surfaces are better radiators than smooth surface

(b) Highly polished mirror like surfaces are very good radiators

(c) Black surfaces are better absorbers than white ones

(d) Black surfaces are better radiators than white

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Half part of ice block is covered with black cloth and rest half is covered with white cloth and then it is kept in sunlight. After some time clothes are removed to see the melted ice. Which of the following statements is correct ?

(a) Ice covered with white cloth will melt more

(b) Ice covered with black cloth will melt more

(c) Equal ice will melt under both clothes

(d) It will depend on the temperature of surroundings of ice

Concept Questions :-

Conduction
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If between wavelength $\mathrm{\lambda }$ and $\mathrm{\lambda }+\mathrm{d\lambda }$, ${\mathrm{e}}_{\mathrm{\lambda }}$ and ${\mathrm{a}}_{\mathrm{\lambda }}$ be the emissive and absorptive powers of a body and ${\mathrm{E}}_{\mathrm{\lambda }}$ be the emissive power of a perfectly black body, then according to Kirchoff's law, which is true ?
(a) ${\mathrm{e}}_{\mathrm{\lambda }}$= ${\mathrm{a}}_{\mathrm{\lambda }}$${\mathrm{E}}_{\mathrm{\lambda }}$           (b) ${\mathrm{e}}_{\mathrm{\lambda }}$${\mathrm{E}}_{\mathrm{\lambda }}$=${\mathrm{a}}_{\mathrm{\lambda }}$
(c) ${\mathrm{e}}_{\mathrm{\lambda }}$${\mathrm{a}}_{\mathrm{\lambda }}$${\mathrm{E}}_{\mathrm{\lambda }}$               (d) ${\mathrm{e}}_{\mathrm{\lambda }}$${\mathrm{a}}_{\mathrm{\lambda }}$${\mathrm{E}}_{\mathrm{\lambda }}$ = constant

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When p calories of heat is given to a body, it absorbs q calories; then the absorbtion power of body will be ?
(a) p/q                          (b) q/p
(c) ${\mathrm{p}}^{2}/{\mathrm{q}}^{2}$                      (d) ${\mathrm{q}}^{2}/{\mathrm{p}}^{2}$

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In rainy season, on a clear night the black seat of a bicycle becomes wet because -

1. It absorbs water vapour

2. Black seat is good absorber of heat

3. Black seat is good radiator of heat energy

4. None of the above

Concept Questions :-

Difficulty Level:

There is a rough black spot on a polished metallic plate. It is heated upto 1400 K approximately and then at once taken in a dark room. Which of the following statements is true ?

(a) In comparison with the plate, the spot will shine more

(b) In camparison with the plate, the spot will appear more black

(c) The spot and the plate will be equally bright

(d) The plate and the black spot can not be seen in the dark room

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Which of the following is the example of ideal black body ?

(a) Kajal                                 (b) Black board
(c) A pin hole in a box              (d) None of these

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A piece of blue glass heated to a high temperature and a piece of red glass at room temperature, are taken inside a dimly lit room. Then  -

1. The blue piece will look blue and red will look as usual

2. Red look brighter red and blue look ordinary blue

3. Blue shines like brighter red compared to the red piece

4.  Both the pieces will look equally red.

Concept Questions :-

Stefan-Boltzmann law
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Which of the following law states that “good absorbers of heat are good emitters”  ?
(a) Stefan’s law                (b) Kirchoff’s law
(c) Planck’s law                (d) Wein’s law

Concept Questions :-

Stefan-Boltzmann law

Difficulty Level:

According to Wein's law -
(a) ${\mathrm{\lambda }}_{\mathrm{m}}\mathrm{T}$= constant                 (b) $\frac{{\mathrm{\lambda }}_{\mathrm{m}}}{\mathrm{T}}$= constant
(c) $\frac{T}{{\mathrm{\lambda }}_{\mathrm{m}}}$= constant                 (d) $\mathrm{T}+{\mathrm{\lambda }}_{\mathrm{m}}$= constant

Concept Questions :-

Wien displacement law