THERMAL PHYSICS – THERMOMETRY – HEAT PROPAGATION
Thermal Physics
Thermometry – Heat Propagation
01-(ENEM-MEC)
The result of direct conversion of solar energy is one of the various forms of alternative energy available. Solar heating is obtained by a dark plate covered in glass, through which a tube containing water passes. The water circulates, as shown in the diagram below.
Source: Adapted from PALZ, Wolfgang, “Solar energy and alternative sources”. Hemus, 1981.
The following statements are made regarding the materials used in the solar heater:
I. the hot water tank must be metallic to conduct heat better.
II. The glass covering has the function of better retaining heat, similar to what happens in a greenhouse.
III. the plate used is dark to better absorb the radiant energy of the Sun, heating the water more efficiently.
Among the statements above, it can be said that only the following is/are correct:
02-(ENEM-MEC)
Food refrigeration and freezing account for a significant portion of the
electrical energy consumption in a typical home. To reduce the heat losses of a refrigerator, some operational precautions can be taken:
I – Distribute the food on the shelves, leaving empty spaces between them, so that cold air can circulate downwards and hot air can circulate upwards.
II – Keep the freezer walls covered with a thick layer of ice, so that the increase in ice mass increases heat exchange in the freezer.
III – Clean the radiator (“grille” at the back) periodically, so that the grease and dust that accumulate on it do not reduce heat transfer to the environment.
For a traditional refrigerator, it is correct to indicate only,
a) operation I
b) operation II
c) operations I and II
d) operations I and III
e) operations II and III
03-(ENEM-MEC)
Jupiter, known as the gas giant, has lost one of its most prominent stripes, leaving its southern hemisphere strangely empty. Note the region where the stripe has disappeared, highlighted by the arrow.
Jupiter’s appearance is typically marked by two dark bands in its atmosphere—one in the northern hemisphere and one in the southern hemisphere. Since the gas is constantly in motion, the disappearance of the band on the planet is related to the movement of the various layers of clouds in its atmosphere. The sunlight reflected from these clouds generates the image that is captured by telescopes, in space or on Earth.
The disappearance of the southern strip may have been determined by a change
a) the temperature of the planet’s surface.
b) in the shape of the planet’s gaseous layer.
c) in the gravitational field generated by the planet.
d) in the chemical composition of the planet’s clouds.
e) the density of the clouds that make up the planet.
04-(ENEM-MEC)
Industrialized cities produce large amounts of gases such as CO2 , the main greenhouse gas. This is due to the amount of fossil fuels burned, mainly in transportation, but also in industrial boilers. In addition, these cities have the largest areas of asphalted and concreted soil, which increases heat retention, forming what are known as “heat islands”. This phenomenon occurs because these materials absorb heat and return it to the air in the form of thermal radiation.
In urban areas, due to the joint action of the greenhouse effect and “heat islands”, it is expected that electricity consumption
a) decrease due to the use of boilers by metallurgical industries.
b) increase due to the blocking of sunlight by greenhouse gases.
c) decrease due to the lack of need to heat water used in industries.
d) increase due to the need for greater cooling in industries and homes.
e) decrease due to the large amount of reused thermal radiation.
05-(ENEM-MEC)
In order to test the efficiency of microwave ovens, it was planned to heat samples of different substances, each with a certain mass, at 10°C in five ovens of different brands.
In this test, each oven operated at maximum power. The most efficient oven was the one that
A) provided the greatest amount of energy to the samples.
B) gave energy to the sample with the greatest mass in a longer period of time.
C) provided the greatest amount of energy in the least amount of time.
D) gave energy to the sample with the lowest specific heat more slowly.
E) delivered the least amount of energy to the samples in the least amount of time.
06-(ENEM-MEC)
When it comes to alternative fuel technology, many energy experts believe
that alcohols will grow in importance in the near future. Indeed, alcohols such as methanol and ethanol have found some niches for domestic use as fuels for many decades and have recently been gaining increasing acceptance as additives, or even as substitutes for gasoline in vehicles.
Some of the physical properties of these fuels are shown in the following table.
Consider that, in small volumes, the production cost of both alcohols is the same. Therefore, from an economic point of view, it is more advantageous to use
a) methanol, since its complete combustion provides approximately 22.7 kJ of energy per liter of fuel burned.
b) ethanol, as its complete combustion provides approximately 29.7 kJ of energy per liter of fuel burned.
c) methanol, as its complete combustion provides approximately 17.9 MJ of energy per liter of fuel burned.
d) ethanol, as its complete combustion provides approximately 23.5 MJ of energy per liter of fuel burned.
e) ethanol, as its complete combustion provides approximately 33.7 MJ of energy per liter of fuel burned.
07-(ENEM-MEC)
The color of a star is related to the temperature on its surface. Not very hot stars
(around 3,000K) appear reddish to us. Yellow stars like the Sun have a temperature of around 6,000K; the hottest stars are white or blue because their temperature is above 10,000K.
The table presents a spectral classification and other data for stars in these classes.
a) 20,000 times the luminosity of the Sun
b) 28,000 times the luminosity of the Sun
c) 28,850 times the luminosity of the Sun
d) 30,000 times the luminosity of the Sun
e) 50,000 times the luminosity of the Sun
08-(ENEM-MEC)
One of the processes used in waste treatment is incineration, which has advantages and disadvantages.
In São Paulo, for example, waste is burned at high temperatures and part of the energy released is transformed into electrical energy. However, incineration causes the emission of pollutants into the atmosphere.
One way to minimize the disadvantage of incineration, highlighted in the text, is
a) increase the volume of incinerated waste to increase the production of electrical energy.
b) encourage the use of filters in incinerator chimneys to reduce air pollution.
c) increase the volume of waste to reduce operational costs related to the process.
d) promote selective waste collection in cities to increase the volume of waste incinerated.
e) reduce the waste incineration temperature to produce a greater amount of electrical energy.
Exercises with ENEM characteristics
09-(UFPR-PR)
Analyze the following statements about concepts of thermology:
I) Heat is a form of energy.
II) Heat is the same as temperature.
III) The quantity that allows us to inform whether two bodies are in thermal equilibrium is temperature.
Only the following is/are correct:
10-(FATEC-SP)
Lord Kelvin (title of nobility given to the famous physicist William Thompson, 1824-1907) established a
association between the agitation energy of the molecules of a system and its temperature.
He deduced that at a temperature of -273.15 ºC, also called absolute zero, the thermal agitation of the molecules should cease. Consider a closed container with gas and a variation in volume
negligible under the conditions of the problem and, for convenience, that absolute zero corresponds to –273 ºC.
The correct statement is:
a) The state of agitation is the same for temperatures of 100 ºC and 100 K.
b) At a temperature of 0 ºC the state of agitation of the molecules is the same as at 273 K.
c) The molecules are more agitated at –173 ºC than at –127 ºC.
d) At –32 ºC the molecules are less agitated than at 241 K.
e) At 273 K the molecules are more agitated than at 100 ºC.
11-(UNIFESP-SP)
The following text was extracted from an article about freezing corpses to preserve them for many years, published in the newspaper O Estado de S. Paulo on 21.07.2002.
After clinical death, the body is cooled with ice. An injection of anticoagulants is administered and a special fluid is pumped into the heart, spreading throughout the body and pushing out the natural fluids. The body is placed in a chamber with nitrogen gas, where the fluids harden instead of freezing. Once the temperature reaches -321º, the body is taken to a tank of liquid nitrogen, where it is placed upside down.
The article does not state the temperature unit used.
Considering that the indicated value of -321º is correct and that it belongs to one of the scales, Kelvin, Celsius or Fahrenheit, it can be concluded that the scale used was:
a) Kelvin, since this is a scientific work and this is the unit adopted by the International System.
b) Fahrenheit, because it is a value lower than absolute zero and, therefore, can only be measured on this scale.
c) Fahrenheit, because the Celsius and Kelvin scales do not allow this numerical temperature value.
d) Celsius, because only it has negative numerical values to indicate temperatures.
e) Celsius, because it is an article published in Portuguese and this is the unit officially adopted in Brazil.
12-(UFPEL-RS)
It is common for the information panel in airplane cabins to display the outside temperature in two ways: in degrees Celsius and in Fahrenheit.
Select the alternative with the graph that correctly represents the temperatures recorded for the air, on the plane’s panel, when it moves from the ground to the top of the clouds.
13-(UNESP-SP)
A student develops a thermometer to be used specifically in his laboratory work.
The idea is to measure the temperature of a medium by reading the electrical resistance of a resistor, a copper wire for example, when in thermal equilibrium with that medium. Thus, to calibrate this thermometer on the Celsius scale, it takes as references the melting temperatures of ice and the boiling temperatures of water. After several measurements, it obtains the curve shown in the figure.
The correspondence between the temperature T, in °C, and the electrical resistance R, in Ω, is given by the equation
a) T = 100.(R – 16) / 6.6.
b) T = 100.6.6 / (R – 16).
c) T = (R – 6.6) / (6.6,100).
d) T = 100.(R – 16) / 16.
e) T = 100.(R – 6.6) / 16.
14-(UFMS-MS)
Through experiments, biologists observed that the singing rate of crickets of a certain species was related to the ambient temperature in a way that could be considered linear.
Experiments have shown that at a temperature of 21°C, crickets chirped an average of 120 times per minute; and at a temperature of 26°C, crickets chirped an average of 180 times per minute. Consider T to be the temperature in degrees Celsius and n to be the number of times the crickets chirped per minute.
Assuming that the crickets chirped an average of 156 times per minute, according to the model suggested in this question, it is estimated that the temperature should be equal to:
below). The bar of length L 1 has thermal conductivity k 1 , and the bar of length L 2 has thermal conductivity k 2 , where k 1 > k 2 . The two ends are maintained at fixed and different temperatures, T 1 and T 2 . Consider the three cross-sections highlighted in the figure. Cross-section 1 is in bar 1; cross-section 2 is in bar 2; and cross-section 3 is in the interface or coupling region of the bars.
it can be correctly stated that
a) the heat flux in cross-section 1 is greater than the heat flux in cross-section 2.
b) the heat flux in cross-section 2 is greater than the heat flux in cross-section 1.
c) the heat flow at the interface is zero.
d) the heat flow is the same in any of the three cross sections.
16-(UFCG-PB)
El Niño is a major environmental phenomenon affecting the planet’s atmosphere. Pressure and temperature conditions are essential for its occurrence. The following drawing is a diagram of the atmospheric circulation over the Pacific Ocean between the Australian continent and the region near the coast of Peru. The surface flow shown in the drawing represents the movement of air masses over the surface of the Pacific.
Regarding the climatic conditions of this region, present in the promotion of El Niño, it can be stated that
a) the rise of large air masses near the ocean, on the coast of Peru, reveals a high temperature zone.
b) near the ocean, on the Australian continent, atmospheric pressure must be very low, which justifies the direction of the surface flow.
c) near the ocean surface, off the coast of Peru, atmospheric pressure must be very high, which justifies the direction of the surface flow.
d) the air near the ocean, on the coast of Peru, must have very low temperatures.
e) the surface flow occurs from a region of very high temperatures to regions of very low temperatures.
17-(UNIMONTES-MG)
A radiometer (see figure) is a device consisting of a transparent bulb, inside which, isolated from the external environment, is a propeller made up of four very light plates. Each plate has a black face on one side and a white face on the other. The propeller can rotate freely (practically without friction).
The radiometer is used to demonstrate how thermal radiation is absorbed differently by dark and light objects. When thermal radiation hits the plates, due to the difference in absorption, the black sides heat up more than the white ones, which generates a convection current that causes air to circulate inside the device and causes the propeller to spin. The visual effect of the radiometer in operation is amazing, which makes it an excellent device for educational purposes.
If a radiometer is initially illuminated with an incandescent lamp (yellow light) and,
subsequently, with a mercury vapor lamp (white light), it is CORRECT to state that
a) the propeller will move faster when illuminated by the mercury vapor lamp, as white light has more thermal energy.
b) the propeller will move faster when illuminated by the mercury vapor lamp, as it also emits ultraviolet radiation, whose wavelength is longer than that of yellow light.
c) the propeller will move faster when illuminated by the incandescent lamp, as this generates a lot of radiation in frequency ranges higher than those generated by the mercury vapor lamp.
d) the propeller will move faster when illuminated by the incandescent lamp, as it generates a lot of infrared radiation, in addition to visible light.
18-(UFGO-GO)
An automobile has a water mixture in its cooling system. This mixture is
pumped, circulating the heat from the engine to the radiator, where the heat is dissipated to the environment. A driver starts the engine of this car and sets off on his journey. After 10 minutes, he observes, on the temperature indicator on the dashboard, that the mixture reaches the radiator at 90 ° C
and remains around that value throughout the trip. This is because
a) the radiator dissipates more heat than the engine produces.
b) the radiator dissipates more heat the higher the temperature of the aqueous mixture.
c) the engine releases less heat when heated above this temperature.
d) the engine stops producing heat above this temperature.
e) the radiator dissipates less heat above this temperature.
19-(UFPEL-RS)
We all know that the presence of water is essential to ensure the existence of life on our planet. A specific behavior of this important substance ensures, for example, that the “friendly” bear in the picture tries to secure its meal by catching the little fish that swims in a lake, below the layer of ice.
The formation of this layer of ice on the surface of the lake, allowing fauna and flora to remain alive in its liquid interior, is due to
a) the irregular expansion of water, which reaches maximum density at a temperature of 4°C.
b) the high specific heat of water, which releases large amounts of heat when cooled.
c) the high thermal conductivity of the ice, which allows the sun to continue to heat the lake water.
d) the solidification temperature of water, which remains equal to 0°C, regardless of the pressure to which it is subjected.
e) the high latent heat of solidification of water, which releases large amounts of heat when it passes into a solid state.
20-(ACAFE-SC)
The greenhouse effect is essential to maintaining the thermal balance of our planet because without it the Earth’s temperature would be approximately -20 ° C. One of the most important gases in this process is carbon dioxide, however, a 10% increase in its concentration would cause the average temperature of the planet to increase by approximately 3 ° C, bringing serious consequences.
for ocean levels and climate. This participation of carbon dioxide occurs because it is _______ to visible radiation and ________ to infrared radiation.
The alternative that completes the statement above, in sequence, is:
a) opaque – opaque
b) opaque – transparent
c) transparent – opaque
d) transparent – transparent
e) absorbent – transparent
21-(BRAZILIAN PHYSICS OLYMPIAD)
A student walks barefoot on a day when the ambient temperature is 28°C. At a certain point, the ceramic floor changes to a wooden floor, both being in thermal equilibrium.
The child then has the sensation that the ceramic was colder than the wood. After reflecting a little, he correctly concludes that:
a) the sensation that the temperatures are different in fact represents physical reality, since ceramics have a lower heat capacity than wood.
b) the sensation that the temperatures are different does not represent physical reality, since ceramics have a lower heat capacity than wood.
c) the sensation that the temperatures are different in fact represents physical reality, since the thermal conductivity of ceramics is greater than that of wood.
d) the sensation that the temperatures are different does not represent physical reality, since the thermal conductivity of ceramics is greater than that of wood.
e) there are not enough physical elements to state whether the thermal sensation corresponds to reality or not, since to do so it would be necessary to know the specific heats of ceramics, wood and also human skin.
22-(UFF-RJ)
Sailing is the sport that has won the most medals for Brazil in the Olympics. In the 2004 Athens Olympics alone, Brazil won two gold medals out of the four.
Knowing that the practice of this sport requires a strong interaction with the geographic space and nature, correctly characterize the
sea breeze.
a) It blows during the day from the ocean (with lower temperature) to the continent (with higher temperature).
b) It blows during the day from the ocean (with lower pressure) to the continent (with higher pressure).
c) It blows during the night from the continent (with higher temperature) to the ocean (with lower temperature).
d) It blows during the night from the continent (with higher pressure) to the ocean (with lower pressure).
e) It blows during the day or during the night, whenever there is rain that reduces the temperature.
23-(UNESP-SP)
A body I is placed inside an evacuated transparent glass bell. On the outside, in an environment at atmospheric pressure, a body II is placed close to the bell, but not in contact with it, as shown in the figure.
The temperatures of the bodies are different and the pins that support them are thermal insulators. Consider the forms of heat transfer between these bodies and indicate the correct alternative.
a) There is no heat exchange between bodies I and II because they are not in contact with each other.
b) There is no heat exchange between bodies I and II because the environment inside the bell is evacuated.
c) There is no heat exchange between bodies I and II because their temperatures are different.
d) There is heat exchange between bodies I and II and the transfer occurs by convection.
e) There is heat exchange between bodies I and II and the transfer occurs through electromagnetic radiation.
24- (UFG-GO)
Rural greenhouses are limited planting areas covered by transparent plastic tarps that
cause, among other things, the internal temperature to be higher than the external temperature. This is because:
a) the heated air next to the canvas descends by convection to the plants.
b) the tarpaulins are more transparent to visible light radiation than to infrared radiation.
c) a continuous net flow of energy is established from outside to inside the greenhouse.
d) the expansion of the air expels the cold air out of the greenhouse.
e) the air trapped in the greenhouse acts as a good conductor of heat, heating the soil.
25-(CPS-SP)
Ana, after listening attentively to a news report about “Walking to de-stress”, decides to follow this practice. So, she walks 9 km from her work, located in the central region, to her home, located in the suburban residential area.
On this route, she passes through the urban residential area and the park, taking 2.5 hours. Based on the graphic scheme and considering that Ana’s internal temperature remains constant throughout the route, it can be stated that
a) there is less heat transfer between Ana and the environment in the central region.
b) the greatest heat transfer between Ana and the environment occurs in the urban residential region.
c) during the journey, the smallest heat exchange between Ana and the environment occurs in the park region.
d) in rural areas there is the possibility of greater heat exchange between Ana and the environment.
e) the difference in temperature between the regions does not interfere with the heat transfer between Ana and the environment.