Every question from past board papers on Heat transfer: conduction, convection, radiation, newest paper first. Open any question for its full worked answer.
Three identical heat conducting rods are connected in series as shown in the figure. The rods on the sides have thermal conductivity \(2K\) while that in the middle has thermal conductivity \(K\). The left end of the combination is maintained at temperature \(3T\) and the right end at \(T\). The rods are thermally insulated from outside. In steady state, temperature at the left junction is \(T_1\) and that at the right junction is \(T_2\). The ratio \(T_1/T_2\) is
A cup of coffee cools from 90°C to 80°C in t minutes, when the room temperature is 20°C. The time taken by a similar cup of coffee to cool from 80°C to 60°C at a room temperature same at 20°C is :
The unit of thermal conductivity is :
The power radiated by a black body is P and it radiates maximum energy at wavelength, \(\lambda_0\). If the temperature of the black body is now changed so that it radiates maximum energy at wavelength \(\frac34\lambda_0\), the power radiated by it becomes nP. The value of n is
Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are \(K_1\) and \(K_2\). The thermal conductivity of the composite rod will be :
A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be :
A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is \(U_1\), at wavelength 500 nm is \(U_2\) and that at 1000 nm is \(U_3\). Wien's constant, \(b = 2.88\times10^{6}\) nmK. Which of the following is correct ?
A body cools from a temperature \(3T\) to \(2T\) in 10 minutes. The room temperature is \(T\). Assume that Newton's law of cooling is applicable. The temperature of the body at the end of next 10 minutes will be
