HCI Worksheet 11 Kinetic Model Transfer of Thermal Energy Temperature (answers) (IP)

Hwa Chong Institution Sec 3 Physics 1 Name: ________________________________________ Class: __________ Date: ___________ Sec 3 Physics Worksheet 11 Kinetic Model of Matter, Transfer of Thermal Energy, Temperature & Thermometry (suggested answers) SECTION A: MULTIPLE CHOICE QUESTIONS 1. Diagram 1 shows smoke particles in a transparent box observed using a microscope. Small points of light are seen to move around, as shown in diagram 2. What does this experiment demonstrate about air molecules? A They are in continuous random motion. B They can be seen through a microscope. C They move more quickly when they are heated. D They move because of collisions with smoke particles. E They give out light when they collide with smoke particles. A 2. The diagram shows a model to demonstrate the behaviour of gas molecules. When the piston is vibrated more rapidly, the wooden disc is forced further up the tube. Weights have to be placed on the disc to return it to its original position. The model represents what happens to a gas when it is A cooled, then compressed. B cooled, then heated. C heated, then compressed. D heated, then cooled. E expanded then cooled. C

Hwa Chong Institution Sec 3 Physics 2 3. The volume of a constant mass of gas in a cylinder is reduced at a constant temperature. The pressure exerted by the molecules of the gas increases because A the gas molecules speed up. B the density of the gas increases. C the gas molecules collide with each other more often. D the gas molecules strike the cylinder walls more often. E there is a smaller area of the cylinder in contact with the gas. D 4. A student observes the Brownian motion of smoke particles in the air with a microscope. She sees moving points of light. These points of light come from A air particles are only moving randomly. B air particles are only vibrating. C smoke particles are only moving randomly. D smoke particles are only vibrating. E both smoke and air particles moving randomly. C 5. Some gas is heated in a sealed container. Which of the following does not increase? A The force due to the collisions between the gas molecules and the container walls. B The number of collisions per second by the gas molecules on the container walls. C The average kinetic energy of gas molecules. D The average speed of the gas molecules. E The average distance between gas molecules. E 6. Some gas trapped in a cylinder is compressed at con stant temperature by a piston. Which of the following will not change? A Density B Mass C Molecular spacing D Pressure E Volume B 7. When the temperature of a gas rises at a constant volume, its molecules A move closer together. B move with greater average speed. C collide with one another less often. D exert smaller forces on one another. E expand. B For an ideal gas, the temperature (in K) of a gas is directly proportional to the average kinetic energy of the gas molecules.

Hwa Chong Institution Sec 3 Physics 3 8. When a solid is heated, which of the following changes occurs? A The density increases. B The latent heat increases. C The melting point increases. D The molecules vibrate more rapidly. E The number of molecules increases. D 9. Which states of matter are very difficult to compress? A Gases only B Gases and liquids only C Gases, liquids and solids D Liquids and solids only E Solids only D In primary schools, we have learnt that matter takes up space. In solids and liquids, the particles are packed at about 10-9 m apart. To force them closer, the electrons of atoms start to repel one another. Interestingly, t he electrons are the ones that require the most space in an atom , not the heavy protons and neutrons. 10. A fixed mass of gas is heated while kept at a constant volume. How do the properties of the molecules of the gas change? Average speed Frequency of collision with walls Average distance apart A Increases Increases Unchanged B Increases Increases Decreases C Increases Unchanged Unchanged D Unchanged Increases Increases E Unchanged Unchanged Decreases A 11. Why does the pressure of a fixed mass of gas increase when it is heated at constant volume? A More molecules are created by heating. B The average mass of the molecules increases. C The average speed of the molecules increases. D The molecular collisions become more elastic. C 12. The Brownian motion of smoke particles is caused by A collisions between air molecules. B collisions between smoke particles. C collisions between smoke particles and air molecules. D convection currents in the air. C

Hwa Chong Institution Sec 3 Physics 4 13. If heat is removed from an object, its temperature will normally A fall. C rise. B fall, then rise. D rise then fall. A Unless a chemical reaction ensues and starts producing heat. 14. An unlit match is held near to a scorching bunsen flame. The match does not get hot enough to light because A the flame is not hot enough. B air is a bad conductor of heat. C the match head reflects radiation. D the flame does not radiate any heat sideways. B Technically, option A is not wrong; if the flame is very hot, it can ignite the matchstick by radiation. Option B is the default answer. 15. How may heat be transferred through a vacuum? A by convection only B by radiation only C by conduction only D by conduction and convection only B 16. Boiling water and ice can exist at the same time in a test tube. What does this experiment show? A Ice conducts heat well. B Metal gauze conducts heat poorly. C Water conducts heat well. D Water conducts heat poorly. D

Hwa Chong Institution Sec 3 Physics 5 17. A copper plate is heated to 100 C . It cools by emitting A electrons. B  -radiation. C infra-red radiation. D ultraviolet radiation. C According to Wien’s law (not in the syllabus), all types of electromagnetic waves can be radiated by an object above absolute zero. However, the different wavelengths do not radiate with the same intensity. The dominant wavelength emitted at ~ 373 K is infra-red. 18. By what process does a beaker of hot water lose energy? A conduction, convection and evaporation only B conduction, convection and radiation only C conduction, convection, evaporation and radiation D evaporation and radiation only C Evaporation removes the latent heat of vaporization from the hot water. Some energy is ne eded to change water from the liquid phase to the gaseous phase. 19. Which types of surface are the best absorbers and the best emitters of infra-red radiation? Best absorber Best emitter A black and dull black and dull B black and shiny white and dull C white and dull black and shiny D white and shiny white and shiny A Note: a good absorber must also be a good emitter. We can use the following example to illustrate this concept: a hot object placed in a room will eventually be cooled down to reach thermal equilibrium with the room. At thermal equilibrium, the rate of absorption and emission rate is the same for the object. If the absorption coefficient is higher than the emission coefficient , then the object can absorb net heat from the room even when it is at a higher temperature. Such a situation will violate the Second Law of Thermodynamics. In the molecular sense, Einstein showed that the probability of absorption for all radiation is the same as the probability of emission. 20. When you stand bare feet with one foot on a stone floor and the other on a carpet, the stone floor feels colder than the carpet. The most likely ex