Emissive and Absorptive Power

Q. 58.If temperature of ideal black body increased by 10% what will be % increase in quantity of radiation emitted from its surface

Q. The graph shown in the adjacent diagram represents the variation of temperature $\left(T\right)$ of two bodies, $x$ and $y$ having same surface area, with time $\left(t\right)$ due to the emission of radiation. Find the correct relation between the emissivity $\left(e\right)$ and absorptivity $\left(a\right)$ of the two bodies.

1. $e_x>e_y$ and $a_x<a_y$
2. $e_x<e_y$ and $a_x>a_y$
3. $e_x>e_y$ and $a_x>a_y$
4. $e_x<e_y$ and $a_x<a_y$

Q. 22. There is a temperature difference of 1K between two black patches of skin on patients chest each patch have area A. The radiant thermal power emitted from them differ by 2%, then temperature of two patches (1) 100K, 101K (2) 300K, 301K (3) 200K, 201K(4) 400K, 401K

Q. The operating temperature of an incandescent bulb (with a tungsten filament) of power $60\text{W}$ is $3000\text{K}$. If the surface area of the filament be $25{\text{mm}}^2$. Find its emissivity $e$.$(\sigma =5.67\times {10}^{-8}\text{W}/{\text{m}}^2-{\text{K}}^4)$

1. $0.52$
2. $0.48$
3. $0.64$
4. $0.36$

Q. The graph shown in the adjacent diagram represents the variation of temperature $\left(T\right)$ of two bodies, $x$ and $y$ having same surface area, with time $\left(t\right)$ due to the emission of radiation. Find the correct relation between the emissivity $\left(e\right)$ and absorptivity $\left(a\right)$ of the two bodies.

1. $e_x>e_y$ and $a_x<a_y$
2. $e_x<e_y$ and $a_x>a_y$
3. $e_x>e_y$ and $a_x>a_y$
4. $e_x<e_y$ and $a_x<a_y$

Q. A spherical body radiates $300\text{W}$ power at $650\text{K}$. If the radius were halved and temperature doubled, then find the power radiated.

1. $600\text{W}$
2. $900\text{W}$
3. $300\text{W}$
4. $1200\text{W}$

Q. A thin brass rectangular sheet of sides $15.0\text{cm}$ and $12.0\text{cm}$ is heated in a furnace to ${527}^{\circ }\text{C}$ and taken out in vacuum. Find the electric power needed to maintain the sheet at this temperature, given that its emissivity is $0.250$.
(Take $\sigma =5.67\times {10}^{-8}{\text{W/m}}^2-{\text{K}}^4$)

1. $300\text{W}$
2. $209\text{W}$
3. $250\text{W}$
4. $400\text{W}$

Q. A spherical body having radius $r$ is radiating energy $Q$ at a given temperature, in a particular time. If its radius is doubled then for same time and temperature, energy radiated will be

1. $\frac{1}{2}Q$
2. $\frac{1}{4}Q$
3. $2Q$
4. $4Q$

Q. The four surfaces used in the Leslie's cube experiment of a cube are kept

1. at different temperatures
2. at same temperature
3. two surfaces at same temperature and two at different temperature
4. three surfaces at same temperature and one at different temperature

Q. A spherical body of area $300{\text{cm}}^2$ has emissive power of $3000{\text{J/m}}^2\text{s}$. Find the amount of thermal energy radiated by the body in $10\text{s}$.

1. $1000\text{J}$
2. $5000\text{J}$
3. $9000\text{J}$
4. $900\text{J}$