To solve important questions of fluid mechanism click on the link given below=
Q.1. Show graphically how the energy emitted from a hot body varies with the wavelength of radiation. Give some of salient points of the graph.
Q.2. Explain why:
(a) a body with large reflectivity is a poor emitter.
(b) a brass tumbler feels much colder than a wooden tray on a chilly day.
.Q.3. Give four reasons why is mercury used in Thermometers
.Q.4. Give some merits of gas thermometers over those of mercury thermometers.
Q.5. Name the suitable thermometers to measure the following temperatures:(i) −80°C(ii) 60°C(iii) 250°C(iv)780°C(v) 2000°C
Q.7. What is meant by coefficient of linear expansion and coefficient of cubical expansion? Derive the
relationship between them.
Q.8. Two large holes are cut in a metal sheet. If the sheet is heated, how will the diameters of the holes change?
Q.9. In the above question (Q.8), will the distance between the two holes increase or decrease on heating?
Q.10. There are two spheres of the same radius and material at the same temperature, but one is solid while the other is hollow. Which sphere will expand more if:(i) They are heated to the same temperature.(ii) The same amount of heat is given to each of them.
Q.11. Two bodies of specific heats c1 and c2 , having same heat capacities are combined to form a single composite body. What is the specific heat of the composite body?
Q.12. Name the three modes of transfer of heat from one object to other. Also cite one example for each one of them.
Q.13. Define coefficient of thermal conductivity. Write its SI unit.
Q.14. Define thermal conduction and convection. How are these modes of transfer different from thermal radiation?
Q.15. Two rods A and B are of equal length. Each rod has its ends at temperatures T1 and T2 . What is the condition that will ensure equal rates of flow of heat through the rods A and B?
Q16. Distinguish between conduction, convection and radiation.
Q.17. Two vessels of different materials are identical in size and wall-thickness. They are filled with equal quantities of ice at 0°C. If the ice melts completely in 10 and 25 minutes respectively, compare the coefficients of thermal conductivity of the materials of the vessels.
Q.18. Two vessels A and B of different materials but having identical shape, size and wall- thickness are filled with ice and kept at the same place. Ice melts at the rate of 100 g min⁻¹ and 150 g min⁻¹ in A and B respectively. Assuming that heat enters the vessels through the walls only, calculate the ratio of thermal conductivities of their materials.
Q.19. Water in a closed tube is heated with one arm placed vertically above an arc lamp. Water will begin to circulate along the tube in a counterclockwise direction. Is this true or false?
Q.20. A sphere, a cube and a thin circular plate, all made of the same material and having the same mass, are initially heated to a temperature of 200°C. Which of these objects will cool fastest and which one slowest when left in air at room temperature? Give reasons.
.21. There are two rods of the same metal, same length, and same area of cross-section, but one of square cross-section and the other of circular cross-section. One end of each is kept immersed in steam. After the steady state is reached, the other ends of the rods are touched. Which one will be hotter? Give reason.
Q.22. Define Newton’s law of cooling. Write the expression.
Q.23. A solid sphere of copper of radius R and a hollow sphere of the same material of inner radius r and outer radius R are heated to the same temperature and allowed to cool in the same environment. Which of them starts cooling faster?
Q.24. On a hot day, a car is left in sunlight with all the windows closed. After some time, it is found that the inside of the car is considerably warmer than the air outside. Explain why.
q.25. How does tea in a thermos flask remain hot for long time?
Q.26. A blackened platinum wire , when gradually heated , first appears dull red then blue and finally white , explain why?
Q.27. In a coal fire, the pockets formed by coals appear brighter than the coals themselves. Is the temperature of such a pocket higher than the surface temperature of a glowing coal?