Two rods, A and B, of different materials having the same cross-sectional area are welded together as shown in the figure. Their thermal conductivities are and . The thermal conductivity of the composite rod will be:
1.
2.
3.
4.
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 watts would be:
1. | 225 | 2. | 450 |
3. | 1000 | 4. | 1800 |
The coefficients of linear expansion of brass and steel rods are α1 and α2, lengths of brass and steel rods are l1 and l2 respectively. If (l2 - l1) is maintained the same at all temperatures, Which one of the following relations holds good?
1. α1l22 = α2l12
2. α12l2 = α22l1
3. α1l1 = α2l2
4. α1l2 = α2l1
A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at a wavelength of 250 nm is U1, at a wavelength of 500 nm is U2 and that at 1000 nm is U3. Given Wien's constant of the following is correct?
1. U3=0
2. U1>U2
3. U2>U1
4. U1=0
A piece of ice falls from a height \(h\) so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice, and all energy of ice gets converted into heat during its fall. The value of \(h\) is: (Latent heat of ice is \(3.4\times10^5\) J/kg and \(g=10\) N/kg)
1. | \(544\) km | 2. | \(136\) km |
3. | \(68\) km | 4. | \(34\) km |
The two ends of a metal rod are maintained at temperatures \(100^{\circ}\mathrm{C}\) and \(110^{\circ}\mathrm{C}\). The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures \(200^{\circ}\mathrm{C}\) and \(210^{\circ}\mathrm{C}\), the rate of heat flow will be:
1. 44.0 J/s
2. 16.8 J/s
3. 8.0 J/s
4. 4.0 J/s
A certain quantity of water cools from \(70^{\circ}\mathrm{C}\) to \(60^{\circ}\mathrm{C}\) in the first 5 minutes and to \(54^{\circ}\mathrm{C}\) in the next 5 minutes.
The temperature of the surroundings will be:
1. | \(45^{\circ}\mathrm{C}\) | 2. | \(20^{\circ}\mathrm{C}\) |
3. | \(42^{\circ}\mathrm{C}\) | 4. | \(10^{\circ}\mathrm{C}\) |
The temperature of a wire of length 1 meter and an area of cross-section 1cm2 is increased from \(0^{\circ} \mathrm {C}\) to \(100^{\circ} \mathrm {C}\). If the rod is not allowed to increase in length, the force required will be: \((\alpha = 10^{-5}/ ^{\circ} \mathrm {C} ~\text{and} ~Y = 10^{11} ~\text{N/m}^2)\)
1. | \(10^3 \mathrm{~N} \) | 2. | \(10^4 \mathrm{~N} \) |
3. | \(10^5 \mathrm{~N} \) | 4. | \(10^9 \mathrm{~N}\) |
A metal bar of length \(L\) and area of cross-section \(A\) is clamped between two rigid supports. For the material of the rod, its Young’s modulus is \(Y\) and the coefficient of linear expansion is \(\alpha\). If the temperature of the rod is increased by \(\Delta t^{\circ} \mathrm{C}\), the force exerted by the rod on the supports will be:
1. \(YAL\Delta t\)
2. \(YA\alpha\Delta t\)
3. \(\frac{YL\alpha\Delta t}{A}\)
4. \(Y\alpha AL\Delta t\)
When two ends of a rod wrapped with cotton are maintained at different temperatures and, after some time, every point of the rod attains a constant temperature, then:
1. | Conduction of heat at different points of the rod stops because the temperature is not increasing |
2. | The rod is a bad conductor of heat |
3. | Heat is being radiated from each point of the rod |
4. | Each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat |