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13.1 Degrees

13.1 Degrees. 1) one Celsius degree 2) one Kelvin degree 3) one Fahrenheit degree 4) both one Celsius degree and one Kelvin degree 5) both one Fahrenheit degree and one Celsius degree. Which is the largest unit: one Celsius degree, one Kelvin degree, or one Fahrenheit degree?.

lysander-theron
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13.1 Degrees

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  1. 13.1 Degrees 1) one Celsius degree 2) one Kelvin degree 3) one Fahrenheit degree 4) both one Celsius degree and one Kelvin degree 5) both one Fahrenheit degree and one Celsius degree Which is the largest unit: one Celsius degree, one Kelvin degree, or one Fahrenheit degree?

  2. 13.1 Degrees 1) one Celsius degree 2) one Kelvin degree 3) one Fahrenheit degree 4) both one Celsius degree and one Kelvin degree 5) both one Fahrenheit degree and one Celsius degree Which is the largest unit: one Celsius degree, one Kelvin degree, or one Fahrenheit degree? The Celsius degree and the Kelvin degree are the same size. The scales only differ by an offset, not by the size of the degree unit. For Fahrenheit, there are 180 degrees between boiling and freezing (212°F–32°F). For Celsius, there are 100 degrees between the same points, so the Celsius (and Kelvin) degrees must be larger.

  3. 13.2 Freezing Cold 1) yes, at 0 °C 2) yes, at -273 °C 3) yes, at 0 K 4) no It turns out that – 40°C is the same temperature as – 40°F. Is there a temperature at which the Kelvin and Celsius scales agree?

  4. 13.2 Freezing Cold 1) yes, at 0 °C 2) yes, at -273 °C 3) yes, at 0 K 4) no It turns out that – 40°C is the same temperature as – 40°F. Is there a temperature at which the Kelvin and Celsius scales agree? The Celsius and Kelvin scales differ only by an offset, which is 273 degrees. Therefore, a temperature on one scale can never match the same numerical value on the other scale. The reason that such agreement is possible for Celsius and Fahrenheit is the fact that the actual degree units have different sizes (recall the previous question).

  5. 13.4 Glasses 1) run hot water over them both 2) put hot water in the inner one 3) run hot water over the outer one 4) run cold water over them both 5) break the glasses Two drinking glasses are stuck, one inside the other. How would you get them unstuck?

  6. 13.4 Glasses 1) run hot water over them both 2) put hot water in the inner one 3) run hot water over the outer one 4) run cold water over them both 5) break the glasses Two drinking glasses are stuck, one inside the other. How would you get them unstuck? Running hot water only over the outer glass will allow the outer one to expand, while the inner glass remains relatively unchanged. This should loosen the outer glass and free it.

  7. 13.5a Steel Expansion I A steel tape measure is marked such that it gives accurate length measurements at room temperature. If the tape measure is used outside on a very hot day, how will its length measurements be affected? 1) measured lengths will be too small 2) measured lengths will still be accurate 3) measured lengths will be too big

  8. 13.5a Steel Expansion I A steel tape measure is marked such that it gives accurate length measurements at room temperature. If the tape measure is used outside on a very hot day, how will its length measurements be affected? 1) measured lengths will be too small 2) measured lengths will still be accurate 3) measured lengths will be too big The tape measure will expand, so its markings will spread out farther than the correct amount. When it is laid down next to an object of fixed length, you will read too few markings for that given length, so the measured length will be too small.

  9. 13.5b Steel Expansion II 1) gets larger 2) gets smaller 3) stays the same 4) vanishes Metals such as brass expand when heated. The thin brass plate in the movie has a circular hole in its center. When the plate is heated, what will happen to the hole?

  10. expansion 13.5b Steel Expansion II 1) gets larger 2) gets smaller 3) stays the same 4) vanishes Metals such as brass expand when heated. The thin brass plate in the movie has a circular hole in its center. When the plate is heated, what will happen to the hole? Imagine drawing a circle on the plate. This circle will expand outward along with the rest of the plate. Now replace the circle with the hole, and you can see that the hole will expand outward as well. Note that the material does NOT “expand inward” to fill the hole!!

  11. 14.1a Thermal Contact I Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? 1) the one with the higher initial temperature 2) the one with the lower initial temperature 3) the one with the greater mass 4) the one with the smaller mass 5) the one with the higher specific heat

  12. 14.1a Thermal Contact I Two objects are made of the same material, but have different masses and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? 1) the one with the higher initial temperature 2) the one with the lower initial temperature 3) the one with the greater mass 4) the one with the smaller mass 5) the one with the higher specific heat Since the objects are made of the same material, the only difference between them is their mass. Clearly, the object with less mass will be much easier to change temperature since there is not much material there (compared to the more massive object).

  13. 14.2 Two Liquids 1)the cooler one 2)the hotter one 3)both the same Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has a higher specific heat?

  14. 14.2 Two Liquids 1)the cooler one 2)the hotter one 3)both the same Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has a higher specific heat? Both liquids had the same increase in internal energy, because the same heat was added. But the cooler liquid had a lower temperature change. Since Q = mcDT, if Qandm are both the same and DT is smaller, then c (specific heat) must be bigger.

  15. 14.3a Night on the Field The specific heat of concrete is greater than that of soil. A baseball field (with real soil) and the surrounding parking lot are warmed up during a sunny day. Which would you expect to cool off faster in the evening when the sun goes down? 1) the concrete parking lot 2) the baseball field 3) both cool off equally fast

  16. 14.3a Night on the Field The specific heat of concrete is greater than that of soil. A baseball field (with real soil) and the surrounding parking lot are warmed up during a sunny day. Which would you expect to cool off faster in the evening when the sun goes down? 1) the concrete parking lot 2) the baseball field 3) both cool off equally fast The baseball field, with the lower specific heat, will change temperature more readily, so it will cool off faster. The high specific heat of concrete allows it to “retain heat” better and so it will not cool off so quickly – it has a higher “thermal inertia.”

  17. 14.4 Calorimetry 1)0 oC 2)20 oC 3)50 oC 4) 80 oC 5) 100 oC 1 kg of water at 100 oC is poured into a bucket that contains 4 kg of water at 0 oC. Find the equilibrium temperature (neglect the influence of the bucket).

  18. 14.4 Calorimetry 1)0 oC 2)20 oC 3)50 oC 4) 80 oC 5) 100 oC 1 kg of water at 100 oC is poured into a bucket that contains 4 kg of water at 0 oC. Find the equilibrium temperature (neglect the influence of the bucket). Since the cold water mass is greater, it will have a smaller temperature change! The masses of cold/hot have a ratio of 4:1, so the temperature change must have a ratio of 1:4 (cold/hot). Q1 = Q2 m1cDT1 = m2cDT2 DT1 / DT2 = m2 / m1

  19. 14.5 MoreCalorimetry 1)0oC 2)between0oC and 50oC 3)50oC 4) between 50oC and 100oC 5) 100oC A 1 kg block of silver (c = 234 J/kg 0C ) is heated to 100 0C, then dunked in a tub of 1 kg of water (c = 4186 J/kg 0C ) at 0 0C. What is the final equilibrium temperature?

  20. 14.5 MoreCalorimetry 1)0oC 2)between0oC and 50oC 3)50oC 4) between 50oC and 100oC 5) 100oC A 1 kg block of silver (c = 234 J/kg 0C ) is heated to 100 0C, then dunked in a tub of 1 kg of water (c = 4186 J/kg 0C ) at 0 0C. What is the final equilibrium temperature? Since cwater >> csilver it takes more heat to change the temperature of the water than it does to change the temperature of the silver. In other words, it is much “harder” to heat the water!! Thus, the final temperature has to be closer to the initial temperature of the water. Q1 = Q2 mc1DT1 = mc2DT2 DT1 / DT2 = c2 / c1

  21. 14.6 Adding Heat If you add some heat to a substance, is it possible for the temperature of the substance to remain unchanged? 1) yes 2) no

  22. 14.6 Adding Heat If you add some heat to a substance, is it possible for the temperature of the substance to remain unchanged? 1) yes 2) no Yes, it is indeed possible for the temperature to stay the same. This is precisely what occurs during a phase change – the added heat goes into changing the state of the substance (from solid to liquid or from liquid to gas) and does not go into changing the temperature! Once the phase change has been accomplished, then the temperature of the substance will rise with more added heat.

  23. 14.7 Hot Potato Will potatoes cook faster if the water is boiling faster? 1) yes 2) no

  24. 14.7 Hot Potato Will potatoes cook faster if the water is boiling faster? 1) yes 2) no The water boils at 100 °C and remains at that temperature until all of the water has been changed into steam. Only then will the steam increase in temperature. Since the water stays at the same temperature, regardless of how fast it is boiling, the potatoes will not cook any faster.

  25. 14.8 Water and Ice 1)0oC 2)between0oC and 50oC 3)50oC 4) greater than 50oC You put 1 kg of ice at 0oC together with 1 kg of water at 50oC. What is the final temperature? • LF = 80 cal/g • cwater = 1 cal/goC

  26. 14.8 Water and Ice 1)0oC 2)between0oC and 50oC 3)50oC 4) greater than 50oC You put 1 kg of ice at 0oC together with 1 kg of water at 50oC. What is the final temperature? • LF = 80 cal/g • cwater = 1 cal/goC • How much heat is needed to melt the ice? • Q = m Lf= (1000g)  (80 cal/g) = 80,000 cal • How much heat can the water deliver by cooling from 50oC to 0oC? • Q = cwaterm DT = (1 cal/goC)  (1000g)  (50oC) = 50,000 cal • Thus, there is not enough heat available to melt all the ice!!

  27. 14.9Ice and Steam 1)between0oC and 50oC 2)50oC 3) between50oC and 100oC 4) 100oC 5) greater than 100oC You put 1 kg of ice at 0oC together with 1 kg of steam at 100oC. What is the final temperature? • LF = 80 cal/g, Lv = 540 cal/g • cwater = 1 cal/goC

  28. 14.9Ice and Steam 1)between0oC and 50oC 2)50oC 3) between50oC and 100oC 4) 100oC 5) greater than 100oC You put 1 kg of ice at 0oC together with 1 kg of steam at 100oC. What is the final temperature? • LF = 80 cal/g, Lv = 540 cal/g • cwater = 1 cal/goC • How much heat is needed to melt the ice? • Q = m Lf= (1000g)  (80 cal/g) = 80,000 cal • How much heat is needed to raise the water temperature to 100oC? • Q = cwaterm DT = (1 cal/goC)(1000g)(100oC) = 100,000 cal • But if all of the steam turns into water, that would release 540,000 cal. Thus, some steam is left over, and the whole mixture stays at 100oC.

  29. 14.12Heat Conduction a)a rug b)a steel surface c) a concrete floor d) has nothing to do with thermal conductivity Given your experience of what feels colder when you walk on it, which of the surfaces would have the highest thermal conductivity?

  30. 14.12Heat Conduction a)a rug b)a steel surface c) a concrete floor d) has nothing to do with thermal conductivity Given your experience of what feels colder when you walk on it, which of the surfaces would have the highest thermal conductivity? All things being equal, bigger k leads to bigger heat loss. From the packet: Steel=50, Concrete=0.8, Human body=0.17, Wool=0.04, in units of W/m*C0).

  31. Three Containers Three containers are filled with water to the same height and have the same surface area at the base, but the total weight of water is different for each. Which container has the greatest total force acting on its base? 1 2 3 1)container 1 2) container 2 3) container 3 4) all three are equal

  32. Three Containers Three containers are filled with water to the same height and have the same surface area at the base, but the total weight of water is different for each. Which container has the greatest total force acting on its base? 1 2 3 1)container 1 2) container 2 3) container 3 4) all three are equal The pressure at the bottom of each container depends only on the height of water above it! This is the same for all the containers. The total force is the product of the pressure times the area of the base, but since the base is also the same for all containers, the total force is the same.

  33. The Straw I 1) water pressure 2) gravity 3) inertia 4) atmospheric pressure 5) mass When you drink liquid through a straw, which of the items listed below is primarily responsible for this to work?

  34. The Straw I 1) water pressure 2) gravity 3) inertia 4) atmospheric pressure 5) mass When you drink liquid through a straw, which of the items listed below is primarily responsible for this to work? When you suck on a straw, you expand your lungs, which reduces the air pressure inside your mouth to less than atmospheric pressure. Then the atmospheric pressure pushing on the liquid in the glass provides a net upward force on the liquid in the straw sufficient to push the liquid up the straw.

  35. Wood in Water I Two beakers are filled to the brim with water. A wooden block is placed in the second beaker so it floats. (Some of the water will overflow the beaker.) Both beakers are then weighed. Which scale reads alarger weight? 2 1 3 same for both

  36. Wood in Water I Two beakers are filled to the brim with water. A wooden block is placed in the second beaker so it floats. (Some of the water will overflow the beaker.) Both beakers are then weighed. Which scale reads alarger weight? 2 1 The block in B displaces an amount of water equal to its weight, since it is floating. That means that the weight of the overflowed water is equal to the weight of the block, and so the beaker in B has the same weight as that in A. 3 same for both

  37. Two Bricks Imagine holding two identical bricks in place under water. Brick 1 is just beneath the surface of the water, while brick 2 is held about 2 feet down. The force needed to hold brick 2 in place is: 1 2 1) greater 2) the same 3) smaller

  38. Two Bricks Imagine holding two identical bricks in place under water. Brick 1 is just beneath the surface of the water, while brick 2 is held about 2 feet down. The force needed to hold brick 2 in place is: 1 2 1) greater 2) the same 3) smaller The force needed to hold the brick in place underwater is: W – FB. According to Archimedes’ Principle, FB is equal to the weight of the fluid displaced. Since each brick displaces the same amount of fluid, then FB is the same in both cases.

  39. Archimedes I An object floats in water with 3/4 of its volume submerged. What is the ratio of the density of the object to that of water? 1) 1/4 2) 1/3 3) 4/3 4) 3/4 5) 2/1

  40. 10.12a Archimedes I An object floats in water with 3/4 of its volume submerged. What is the ratio of the density of the object to that of water? 1) 1/4 2) 1/3 3) 4/3 4) 3/4 5) 2/1 Remember that we have: so if the ratio of the volume of the displaced water to the volume of the object is 3/4, the object has 3/4 the density of water.

  41. 10.12b Archimedes II The object is now placed in oil with a density half that of water. What happens? 1) it floats just as before 2) it floats higher in the water 3) it floats lower in the water 4) it sinks to the bottom

  42. 10.12b Archimedes II The object is now placed in oil with a density half that of water. What happens? 1) it floats just as before 2) it floats higher in the water 3) it floats lower in the water 4) it sinks to the bottom We know from before that the object has 3/4 the density of water. If the water is now replaced with oil, which has 1/2 the density of water, the density of the object is larger than the density of the oil. Therefore, it must sink to the bottom.

  43. 10.15a Fluid Flow Water flows through a 1-cm diameter pipe connected to a 1/2-cm diameter pipe. Compared to the speed of the water in the 1-cm pipe, the speed in the 1/2-cm pipe is: (1) one quarter (2) one half (3) the same (4) double (5) four times

  44. 10.15a Fluid Flow Water flows through a 1-cm diameter pipe connected to a 1/2-cm diameter pipe. Compared to the speed of the water in the 1-cm pipe, the speed in the 1/2-cm pipe is: v1 v2 (1) one quarter (2) one half (3) the same (4) double (5) four times The area of the small pipe is less, so we know that the water will flow faster there. Since A r2, when the radius is reduced by1/2, the area is reduced by 1/4, so the speed must increase by 4 times to keep the flow rate (A v) constant.

  45. On Golden Pond A boat carrying a large chunk of steel is floating on a lake. The chunk is then thrown overboard and sinks. What happens to the water level in the lake? 1) rises 2) drops 3) remains the same 4) depends on the size of the steel

  46. On Golden Pond A boat carrying a large chunk of steel is floating on a lake. The chunk is then thrown overboard and sinks. What happens to the water level in the lake 1) rises 2) drops 3) remains the same 4) depends on the size of the steel Initially the chunk of steel “floats” by sitting in the boat. The buoyant force is equal to the weight of the steel, and this will require a lot of displaced water to equal the weight of the steel. When thrown overboard, the steel sinks and only displaces its volume in water. This is not so much water -- certainly less than before -- and so the water level in the lake will drop.

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