General
✓✗The length of a wire is 1.0 m when the tension in it is 4 N and 1.1 m when the tension is 6 N. Its natural length is
- 0.7 m
- 0.8 m
- 0.9 m
- 0.95 m
General
✓✗Two layers of equal thickness and area with conductivities 3K and K are placed in contact. The outer face of the 3K layer is at 100°C and that of the K layer at 20°C. In steady state, the interface temperature is
- 40°C
- 60°C
- 80°C
- 70°C
General
✓✗Two identical mercury drops, each of radius r, merge into a single drop. If S is the surface tension, the energy released is
- 4πr2S(2 − 21/3)
- 4πr2S
- 8πr2S
- 4πr2S(2 − 22/3)
General
✓✗A black body at 2000 K has \( \lambda_m \) = 1.45 μm. A second black body radiates 16 times as much power per unit area. Its \( \lambda_m \) is
- 1.45 μm
- 0.725 μm
- 0.36 μm
- 2.9 μm
General
✓✗Which of the following is more elastic?
- Steel
- Clay
- Glass wool
- Rubber
General
✓✗On a new scale of temperature (which is linear) and called the W scale, the freezing and boiling points of water are 39°W and 239°W respectively. What will be the temperature on the new scale, corresponding to a temperature of 39°C on the Celsius scale?
- 78°W
- 200°W
- 117°W
- 139°W
General
✓✗In a hydraulic lift, the areas of the small and large pistons are 1 cm2 and 100 cm2. A force of 10 N on the small piston can support a load of
- 100 N
- 10 000 N
- 1000 N
- 10 N
General
✓✗Two black bodies of the same surface area are at 400 K and 200 K. The ratio of the powers they radiate is
- 4 : 1
- 16 : 1
- 8 : 1
- 2 : 1
General
✓✗A metal sphere of radius R is lowered into the sea to a depth h. If \( \rho \) is the density of sea water and B the bulk modulus of the metal, the decrease in the radius is about
- \( \dfrac{\rho g h}{3BR} \)
- \( \dfrac{\rho g h R}{3B} \)
- \( \dfrac{\rho g h R}{B} \)
- \( \dfrac{3\rho g h R}{B} \)
General
✓✗Water is poured into a large tank at a steady rate so that its level stays 5 m above a small hole of area 1 cm2 at its bottom. Taking g = 10 m s−2, the rate at which water must be poured in is
- 1 L s−1
- 10 L s−1
- 0.1 L s−1
- 0.5 L s−1
General
✓✗Heat is supplied at a constant rate to a substance. The flat portion during boiling is longer than that during melting because
- latent heat of vaporisation is larger than latent heat of fusion
- boiling point is higher
- the liquid is denser
- specific heat of the liquid is small
General
✓✗An air bubble of radius r rises steadily through a liquid of density \( \rho \) and viscosity \( \eta \) (air density negligible). Its terminal speed is
- \( \dfrac{r^2\rho g}{9\eta} \)
- \( \dfrac{2r^2\rho g}{3\eta} \)
- \( \dfrac{2r^2\rho g}{9\eta} \)
- \( \dfrac{9r^2\rho g}{2\eta} \)
General
✓✗For most metals, the shear modulus G compared with the Young's modulus Y is
- equal to Y
- about 10Y
- about Y/3
- about 3Y
General
✓✗When heat flows through a composite wall in steady state, the layer with the lowest thermal conductivity has
- the smallest temperature drop
- the largest heat current
- the largest temperature drop
- zero temperature drop
General
✓✗A burn from steam at 100°C is more severe than one from water at 100°C because
- water has a lower specific heat
- steam has a lower density only
- steam releases extra latent heat when it condenses
- steam is hotter than 100°C