Embibe Experts Solutions for Chapter: Heat Transfer, Exercise 5: Exercise (Analytical Questions)

Spheres $P \text{and }Q$ are uniformly constructed from the same material which is a good conductor of heat and the radius of $Q$ is thrice of radius of $P$. The rate of fall of temperature of $P$ is $x$ times that of $Q$ when both are at the same surface temperature. The value of $x$ is 

A sphere, a cube and a thin circular plate all made of same substance and all have same mass, These are heated to $200 º\mathrm{C}$ and then placed in a room, then the 

The power radiated by a black body is $P$, and it radiates maximum energy around the wavelength ${\lambda }_0$. If the temperature of the black body is now changed, so that, it radiates maximum energy around a wavelength $\frac{3{\lambda }_0}{4}$, the power radiated by it will increase by a factor of

A slab consists of two parallel layers of copper and brass of the same thickness and having thermal conductivities in the ratio $1 : 4$. If the free face of brass is at $100 º\mathrm{C}$ and that of copper at $0 º\mathrm{C}$, the temperature of interface is 

Out of the metal balls of same diameter one is solid and other is hollow. Both are heated to the same temperature at $300 º\mathrm{C}$ and then allowed to cool in the same surroundings then rate of loss of heat will be 

For a black body at temperature $727 °\mathrm{C}$, its radiating power is $60 \mathrm{W}$ and the temperature of the surrounding is $227 °\mathrm{C}$. If temperature of black body is changed to $1227{ }^{°}\mathrm{C}$, then its radiating power will be

Three discs $A, B$ and $C$ having radii $2 \mathrm{m}, 4 \mathrm{m}$ and $6 \mathrm{m}$ respectively are coated with carbon black on their outer surfaces. The wavelengths corresponding to maximum intensity are $300 \mathrm{nm}, 400 \mathrm{nm}$ and $500 \mathrm{nm}$ respectively. The power radiated by them are $Q_A, Q_B$ and $Q_c$ respectively then

The spectral emissive power $E_{\lambda }$ for a body at temperature T₁ is plotted against the wavelength and area under the curve is found to be A. At a different temperature T₂, the area is found to be 9A. Then ${\lambda }_1/{\lambda }_2=$