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Final Physics Reminders

Posted on October 31, 2012 at 3:45 AM

Final Reminders Physics Answers

Kinetic Particle Theory

1. The air molecules move in random direction. They collide on the smoke particles in all directions with uneven forces. The smoke particles will move in the direction of the resultant force.

2. See above.

3. Standard, temperature increases, kinetic energy increases.

4. During melting, heat energy is taken in increases the potential energy of the particles. The increase in potential energy causes particles to move apart. Since the kinetic energy remains unchanged, the temperature remains constant.

 

Transfer of thermal energy

1. When heat is applied, the particles gain energy and vibrate faster. This causes the particles to collide on neighbouring particle and thus transferring the energy to them. This process of collision and vibration continues till the whole solid is heated up.

2. When heat is applied, the particles gain energy and vibrate faster. This causes the particles to collide on neighbouring particle and thus transferring the energy to them. Good conductors like metals also contain free moving electrons. When the electrons gain energy, it moves faster and collide with other particles quickly, thus transferring the energy.

3. When the liquid is heated, it gains energy and expands. The volume of the liquid increases and for the same mass of liquid, it becomes less dense. The less dense liquid will rise and the cooler and denser liquid at the top will sink to the bottom to be heated. This sets up a convection current that heats up the entire liquid.

4. Simply, the transfer of heat is by electromagnetic radiation.

5. During the day, the land, being a better conductor of heat, gains heat faster than the sea. The warmer air above the land rises and the cooler air from the sea moves in to create the sea breeze. During the night, the land, being a better conductor of heat, loses heat faster than the sea. The warmer air above the water rises and the cooler air from the land moves in to create the land breeze.

6. Dark coloured, dull and rough surfaces are better absorber and emitter of radiation.

7. Insert rods of same dimension but different materials into a hot water tub. Stick a piece wax at the end of each rod, the rod that is the best conductor will be the rod that melts the wax first.

8. Place equal amount of water at 20˚C in 2 cups, 1 painted black, the other white. Place the 2 cups under the hot sun and insert a thermometer in each of the cup. The cup with the black surface will have a faster increase in temperature indicating that a black surface is a better absorber of heat. (For emitter use, hot water at 80˚C in a cool room, check that the black surface cools faster)

9. Heat some water in a beaker to boil. When it boils, add in a potassium manganate crystal at the bottom of the beaker. The crystal will dissolve to form a purple streak indication the path of the convection current.

10. The lid is to reduce heat loss by convection.

11. The vacuum flask has 3 features that keeps a liquid hot. First there is a vacuum layer between the walls of the container which prevents heat loss by conduction and convection. Secondly, its shiny inner walls will reflect heat back into the liquid to keep it hot. The bottle also has a plastic stopper at the top to reduce heat loss by convection.

12. The doubled layer window has a layer of air between them. Since the air is a poor conductor of heat, it keeps the room cool when temperature is high and keeps it warm when outside temperature is cold.

 

Temperature (Pure)

1. Volume of a fixed mass of liquid, pressure of a fixed volume of gas

2. 0 and 100˚C

3. -

4. Place an uncalibrated liquid in glass in pure melting ice. Measure the length of mercury in melting ice. Place the thermometer in steam just above the boiling water, measure the length of mercury. Finally place the thermometer in the unknown substance, measure its length. Find the temperature of the unknown by using the formula _______.

5. Use thinner bulb of thermometer.

6. Use thinner capillary tube.

 

 

Thermal Properties

1. Specific heat capacity measures the amount of energy needed to raise the temperature of a unit mass of substance by 1 ˚C while heat capacity measures the amount of energy needed to raise the temperature of a substance by 1˚C. (Pure)

2. See above

3. The more energetic particles on the surface gains sufficient energy and overcomes the forces of attraction holding the particles together. The average kinetic energy of the liquid decreases after the evaporation, hence energy decreases.

4. Evaporation occurs at all temperature and boiling occurs only at boiling point. Evaporation occurs on the surface and boiling occurs throughout the liquid. Evaporation results in cooling but boiling does not.

Waves

1. definition

2. definition

3. Period is the time taken for a complete oscillation. Frequency measures the number of complete oscillation in 1 sec.

4. -

5. Longitudinal wave - particles vibrate parallel to wave motion but for transverse it is perpendicular.

 

 

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