List of top Physics Questions on radiation

Two black bodies emit the same amount of radiation per second. The radius of the first is \( R_1 = 2 \, \text{m} \) and its temperature is \( T_1 = 400 \, \text{K} \). If the second body has a radius \( R_2 = 4 \, \text{m} \), what is its temperature \( T_2 \) in Kelvin?
Two statements are given one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A): X-rays are produced when slow moving electrons are stopped by a metal target of high atomic number.
Reason (R): X-rays consist of low-energy photons.
A source produces monochromatic light of frequency \( 5.0 \times 10^{14} \, \text{Hz} \) and the power emitted is 3.31 mW. The number of photons emitted per second by the source, on an average, is:
A radioactive substance has a half-life of 5 years. What is the probability that a single atom of this substance will decay within 5 years?
A star 'A' has radiant power equal to 3 times that of the Sun. The temperature of star 'A' is \( 6000 \, \mathrm{K} \) and that of the Sun is \( 2000 \, \mathrm{K} \). What is the ratio of their radii?

A bowl filled with very hot soup cools from $98^{\circ} C$ to $86^{\circ} C$ in 2 minutes when the room temperature is $22^{\circ} C$. How long it will take to cool from $75^{\circ} C$ to $69^{\circ} C$ ?

Match List I with List II:
List IList II
AMicrowavesiRadioactive decay of the nucleus
BGamma wavesiiRapid acceleration and deceleration of electrons in aerials
CRadio wavesiiiInner shell electrons
DX - raysivKlystron valve
Choose the correct answer from the options given below:
Parallel rays of light of intensity I=912 Wm$^{-2}$ are incident on a spherical black body kept in surroundings of temperature 300 K . Take Stefan constant $\sigma =5.7 \times 1^{-8} Wm ^{-2} K^{-4}$ and assume that the energy exchange with the surroundings is only through radiation The final steady state temperature of the black body is close to
The wavelength of radiation emitted by a body depends upon:

Figure shows a copper rod joined to a steel rod. The rods have equal length and equal cross-sectional area. The free end of the copper rod is kept at 0°C and that of steel rod is kept at 100°C. Find the temperature of the junction of the rod. 
Conductivity of copper = \( 390 \, \text{W/m°C} \)
Conductivity of steel = \( 46 \, \text{W/m°C} \)

If the radius of a star is \( R \) and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is \( Q \)?
The radiation emitted by a perfectly black body is proportional to: