Science: Heat Unit Exam Mr. Brovold
Name: Answer Key: Examples of 4-point questions Division ______
You may earn up to 4 marks for each question, depending on the level of understanding you demonstrate and the amount of relevant detail you include in your answer. As always, do your neatest and very best work.
1. Name three natural sources of heat. Sunlight, lightening, body heat, geothermal heat, meteorites
2. Define, with detail, the concept of “heat”. Thermal energy, the transfer of energy from a warmer object to a cooler object. The molecules in hot items are excited and show more rapid movement than cooler objects.
3. You blow up a balloon inside a warm classroom, and then walk outside, where it’s below freezing. What happens to the balloon, and why? The balloon loses heat to the outside air, and the molecules of air inside the balloon became less active, taking up less space, causing it to contract (shrink) and become smaller. The mass of the air inside the balloon did not change.
4. Explain the results of the experiment with the three buckets of water. What type of heat transfer is happening here? When the hand from the hot water was placed into the middle (room temp.)tub, the heat from the hand transferred to the cooler water, giving the sensation of coolness, and created a convection current in the cooler water; when the hand from the ice water was placed into the middle bucket, the heat was transferred to the hand, and made it feel warmer.
5. Name the type of heat transfer that occurs:
o Barbecue conduction convection
o electric stove heating a frying pan conduction o the sun warming the earth radiation
o wind patterns on the Earth convection
6. Compare and contrast radiant heat transfer and conductive heat transfer, and give examples. Both transfer thermal energy from a warmer object to a cooler object. In conduction, the objects are touching and the molecules collide. In radiation, the transfer takes place across space without touching each other. The heat is absorbed by the cooler object.
7. An object feels cold to the touch. Why is this happening? What does that tell you about the object? It means that the object you are touching is cooler (contains less thermal energy), therefore your body heat is transferred to the object. The loss of body heat in this area creates a sensation of coldness.
8. Why do we use an oven mitt to take a hot cake pan out of the oven? What scientific name would we give to what it does? The mitt acts as a barrier of air, which is a poor conductor of heat, between the objects and slows down the conduction of heat from the warmer object to the cooler object. This is called insulation.
9. You are going on a long hike in the mountains in January. Describe two features of the clothing you will wear in order to stay warm, and give reasons. Wear dark clothing that absorbs the sun’s heat, and well-insulated clothing to slow down body heat loss.
10. How does a thermometer work? When the temperature rises, the bulb of liquid absorbs heat, causing it to vibrate and expand (thermal expansion). The expanding liquid has no place to go but up into the tube, the distance depending on the temperature. When the temperature cools, the liquid contracts and moves back down the tube. 11. How does throwing sand on a fire put it out? Use the Fire Triangle in your answer. The sand smothers the fire, cutting off the oxygen supply, which is one of the elements of the fire triangle (fuel, oxygen, heat).
12. What are some things that may prevent some of the sun’s light energy from warming the earth, and why? Some areas on the earth’s surface are white or light-coloured, which reflects radiant heat, for example, mountaintops and glaciers, clouds, other atmospheric conditions.
13. How can heat from the sun affect global weather systems? The light energy from the sun transfers heat to air and water in the areas of most direct sunlight, which create warm air and water currents that move towards cooler areas, displacing cooler air and water (convection).
14. Define the term, ‘geothermal’. Give an example of a geothermal source of heat. Geothermal energy is heat that comes from deep in the Earth, usually from a volcano, a magma chamber, or radioactive decay in the Earth's core.
15. What do liquid thermometers and geysers have in common? They both operate on the principle of thermal expansion of liquids due to a source of heat, and they refill when cooled.
16. Explain the value of the experiment with the food colouring in the hot and cold water. What was the independent variable? The differences in the way the food colouring reacted in the cold water (nearly motionless) and hot water (moving quickly into the water) showed us that molecules move more rapidly when they have been heated, and that other objects will dissolve more quickly in heated water. The temperature is the independent variable.
BONUS QUESTION (as discussed in class): The application or removal of heat can change the state of matter of an object. Explain and support this statement. Use examples. The three states of matter are solid, liquid, and gas. When heat energy is applied to a solid object, the molecules vibrate more rapidly, causing them to separate and change the object to a liquid. If more heat is applied, the liquid may vibrate rapidly enough that the molecules separate and turn into a gas. Removal of heat may reverse the process, condensing gas back into a liquid, and turning liquid back into a solid. For example, heat applied to ice (a solid) will cause it to melt to water (liquid). More heat will cause the liquid to evapourate into steam (a gas). Removal of heat from the gas will cause it to condense back into a liquid, and then eventually into a solid.