## Saturday, 6 September 2014

### THERMAL EFFECTS AND FIELDS PROBLEMS

THERMAL EFFECTS AND FIELDS

Take G = 6.67x10-11 Nm2kg-2                                        Permittivity of free space (Ɛo)= 8.84x10-12 Fm-1 Electron charge = -1.6x10-19C                                                        Electron mass = 9.1x10-31 kg

1. What is an adiabatic change?
2. What is the definition of gravitational potential energy?
3. What is meant by escape velocity?
4. Define specific heat capacity.
5. Define electrical potential.
6. Define an isothermal change.
7. What is meant by the greenhouse effect?
8. What determines whether a planet can retain its atmosphere?
9. Give two similarities between electrostatic force and gravitational force.
10. Write down the first law of thermodynamics, explaining all the symbols that you use.
11. In thermal conductivity if a metal pipe is lagged with an equal thickness of insulator:
(a) Across which will there be the greatest temperature difference or are they equal
(b) Through which will there be the greatest heat flow or are they equal?
12. Give two differences between electrostatic force and gravitational force.
13. What is the electric field inside a hollow charge conductor?
14. How does the electrical potential vary between two parallel charged plates?
15. How does the electric field vary between two parallel charges plates?
16. In gas equations do you use Kelvin or Centigrade?
17. Write down two assumptions made when deriving the kinetic theory of gases equation.
18. Under what conditions is Boyle’s law obeyed most closely for a real gas?
19. What is the change in internal energy for an ideal gas undergoing an isothermal change?
20. What is another way of writing the gravitational potential gradient in a field?
21. What are the units for electrical potential?
22. Write down two alternative units for the electric field intensity.
23. Write down an equation relating the root mean square velocity of gas molecules to the gas density defining any terms that you use.
24. What happens to a beam of light near a neutron star and why?
25. What is a black hole?
26. Write down an expression for Boltzmann’s constant.
27. What is the energy of a gas molecule of mass m at temperature T?
28. Give three properties of a synchronous of geostationary satellite.
29. Between which points on two planets must their separation be measured when calculating the gravitational attraction between them?
30. Define specific latent heat.
31. What happens to the temperature of a material while it is changing its state?
33. Which type of surface is the best emitter of thermal radiation?
34. What is the heat input for an ideal gas undergoing an adiabatic change?
35. Define absolute zero.
36. Define the triple point of water.
37. Define the unit of temperature (K).
38. Write down an equation for the energy changes for an electron being accelerated in a uniform electric field.
39. What is the relation between the electric field intensity at a point in a field and the force on a charge Q placed at that point?
40. What is the formula for the electric field intensity at a distance R from a point charge Q in a vacuum?
41. What is the formula for the electrical force on a charge q at a distance R from a point charge Q in a vacuum?
42. Write down two uses of static electricity.
43. A gas of volume 5m3 at a temperature of 18oC is heated to 100oC, the pressure rising from 1.0x105 Pa to 2.4x105 Pa. What is the new volume of the gas?
44. An electric field exists between two parallel plates 10cm apart and with a potential difference of 400V between them. Calculate the electric field intensity at a point 5 cm from the positive plate
45. Calculate the value of the gravitational intensity at the surface of a planet of mass 5x1025 kg and radius 3x105 m.
46. What is o?
47. How much energy is needed to vaporise 3.5 kg of water at 100 oC? The specific latent heat of vaporisation of water is 2.25x106 Jkg-1.
48. A gas is expanded isothermally, expanded adiabatically, compressed isothermally and finally compressed adiabatically. What is the area of the closed loop on the PV diagram equal to?
49. A vacuum flask contains liquid nitrogen. The outer surface of the inner walls of the flask is silvered – why?
50. How can you get an indication of the electric field intensity from a diagram showing the field lines?
51. Calculate the increase in velocity of an electron that has been accelerated through a potential difference of 2.5 kV.
52. Define electrical potential energy.
53. Define electric field intensity.
54. Which emits radiation of longer wavelength – a black body at 300 oC or a black body at 500 K?
55. If the Earth takes 365 days to orbit the sun at a distance of 150x109 m calculate the mass of the Sun.
56. In an adiabatic expansion does the temperature of a gas rise or fall?
57. In an isothermal compression does heat energy enter or leave the system?
58. Write down the equation that you would use to find the charge (Q) on an oil drop of mass m suspended in an electric field of intensity E.
59. Such a drop is held between two horizontal plates 20 mm apart with a p.d of 250V between them. The drop has a mass of 0.2 mg. Calculate the charge on the drop.
60. A gas is compressed isothermally, expanded adiabatically, expanded isothermally, and finally compressed adiabatically. What is the area of the closed loop on the PV diagram equal to?
61. What is the root mean square velocity of the molecules in a gas of density 1.04 kgm-3 at a pressure of
105 Pa?
62. Why do breezes blow from the sea to the land in the evening after a hot day?
63. What are the units for thermal conductivity?