Which Sample Is Most Likely To Undergo The Smallest Change In Temperature

Department Learning Objectives

Past the finish of this department, y'all will be able to exercise the following:

• Explain heat, rut capacity, and specific heat
• Distinguish between conduction, convection, and radiations
• Solve issues involving specific heat and heat transfer

Instructor Support

Instructor Support

The learning objectives in this section will help your students master the following standards:

• (6) Science concepts. The pupil knows that changes occur within a physical organization and applies the laws of conservation of energy and momentum. The student is expected to:
  • (F) contrast and give examples of unlike processes of thermal free energy transfer, including conduction, convection, and radiation.

Section Key Terms

conduction

convection

heat capacity

radiation

specific heat

Teacher Support

Teacher Back up

[BL] [OL] [AL] Review concepts of estrus, temperature, and mass.

[AL] Bank check prior knowledge of conduction and convection.

Heat Transfer, Specific Rut, and Heat Capacity

We learned in the previous department that temperature is proportional to the average kinetic energy of atoms and molecules in a substance, and that the boilerplate internal kinetic free energy of a substance is higher when the substance's temperature is higher.

If two objects at dissimilar temperatures are brought in contact with each other, energy is transferred from the hotter object (that is, the object with the greater temperature) to the colder (lower temperature) object, until both objects are at the same temperature. There is no net oestrus transfer once the temperatures are equal because the corporeality of heat transferred from one object to the other is the same as the corporeality of heat returned. One of the major effects of heat transfer is temperature modify: Heating increases the temperature while cooling decreases it. Experiments show that the heat transferred to or from a substance depends on three factors—the change in the substance's temperature, the mass of the substance, and certain physical properties related to the phase of the substance.

The equation for heat transfer Q is

where g is the mass of the substance and ΔT is the change in its temperature, in units of Celsius or Kelvin. The symbol c stands for specific estrus, and depends on the material and phase. The specific heat is the corporeality of heat necessary to modify the temperature of 1.00 kg of mass by 1.00 ºC. The specific heat c is a belongings of the substance; its SI unit is J/(kg $\cdot$ One thousand) or J/(kg $\cdot$ $\text{°C}$ ). The temperature change ( $\Delta T$ ) is the aforementioned in units of kelvins and degrees Celsius (simply not degrees Fahrenheit). Specific heat is closely related to the concept of heat chapters. Estrus capacity is the amount of rut necessary to change the temperature of a substance by 1.00 $\text{°C}$ . In equation form, heat chapters C is $C=mc$ , where g is mass and c is specific oestrus. Note that estrus capacity is the same as specific heat, but without any dependence on mass. Consequently, two objects made up of the aforementioned material merely with different masses volition have different heat capacities. This is considering the heat capacity is a property of an object, merely specific heat is a property of any object made of the same material.

Values of specific heat must exist looked upward in tables, because there is no uncomplicated way to calculate them. Table 11.two gives the values of specific rut for a few substances as a handy reference. We run across from this tabular array that the specific heat of h2o is five times that of glass, which ways that it takes five times as much oestrus to raise the temperature of 1 kg of water than to heighten the temperature of one kg of glass by the same number of degrees.

Teacher Support

Teacher Support

[BL] [OL] [AL]Explicate that this formula just works when there is no change in phase of the substance. The transfer of thermal free energy, oestrus, and phase change will be covered later in the affiliate.

Misconception Alarm

The units of specific heat are J/(kg $\cdot \text{°C}$ ) and J/(kg $\cdot$ Grand). Still, degrees Celsius and Kelvins are not always interchangeable. The formula for specific heat uses a difference in temperature and not absolute temperature. This is the reason that degrees Celsius may be used in place of Kelvins.

Substances	Specific Oestrus (c)
Solids	J/(kg $\cdot \text{°C}$ )
Aluminum	900
Asbestos	800
Physical, granite (average)	840
Copper	387
Glass	840
Gold	129
Human body (average)	3500
Ice (average)	2090
Iron, steel	452
Lead	128
Silverish	235
Wood	1700
Liquids
Benzene	1740
Ethanol	2450
Glycerin	2410
Mercury	139
Water	4186
Gases (at one atm constant pressure)
Air (dry)	1015
Ammonia	2190
Carbon dioxide	833
Nitrogen	1040
Oxygen	913
Steam	2020

Tabular array 11.two Specific Heats of Various Substances.

Snap Lab

Temperature Alter of State and Water

What heats faster, state or h2o? Yous will reply this question by taking measurements to study differences in specific heat capacity.

• Open flame—Tie back all loose pilus and habiliment before igniting an open flame. Follow all of your instructor's instructions on how to ignite the flame. Never leave an open up flame unattended. Know the location of fire safety equipment in the laboratory.

• Sand or soil
• Water
• Oven or heat lamp
• 2 small jars
• Two thermometers

Instructions

Procedure

1. Place equal masses of dry out sand (or soil) and water at the same temperature into two small jars. (The average density of soil or sand is about one.6 times that of water, and then you tin can get equal masses by using 50 percent more water past volume.)
2. Heat both substances (using an oven or a heat lamp) for the same amount of time.
3. Record the final temperatures of the two masses.
4. Now bring both jars to the aforementioned temperature past heating for a longer flow of time.
5. Remove the jars from the heat source and measure their temperature every v minutes for about 30 minutes.

Soil has an approximate specific estrus of 800 J / kg °C. A farmer monitors both the soil temperature of his field and the temperature of a nearby pond as winter sets in. Will the field or the pond accomplish 0 °C first and why?

1. The pond volition reach 0 °C beginning because of water's greater specific oestrus.

2. The field will reach 0 °C get-go because of soil'southward lower specific oestrus.

3. They will achieve 0° C at the same time because they are exposed to the same weather condition.

4. The h2o will have longer to heat as well as to absurd. This tells united states that the specific heat of h2o is greater than that of state.

Conduction, Convection, and Radiation

Whenever at that place is a temperature deviation, heat transfer occurs. Estrus transfer may happen speedily, such as through a cooking pan, or slowly, such as through the walls of an insulated cooler.

There are three different heat transfer methods: conduction, convection, and radiation. At times, all three may happen simultaneously. Encounter Figure 11.3.

Effigy 11.3 In a fireplace, heat transfer occurs by all three methods: conduction, convection, and radiation. Radiation is responsible for most of the heat transferred into the room. Heat transfer also occurs through conduction into the room, but at a much slower rate. Heat transfer past convection also occurs through cold air entering the room around windows and hot air leaving the room by rising up the chimney.

Conduction is heat transfer through direct physical contact. Heat transferred between the electric burner of a stove and the bottom of a pan is transferred by conduction. Sometimes, nosotros effort to control the conduction of heat to make ourselves more comfortable. Since the rate of rut transfer is different for different materials, we choose fabrics, such as a thick wool sweater, that irksome down the transfer of oestrus away from our bodies in winter.

Equally you walk barefoot across the living room rug, your feet feel relatively comfortable…until you step onto the kitchen's tile flooring. Since the carpeting and tile floor are both at the aforementioned temperature, why does one feel colder than the other? This is explained by dissimilar rates of oestrus transfer: The tile textile removes heat from your skin at a greater rate than the carpeting, which makes information technology feel colder.

Instructor Back up

Teacher Back up

[BL] [OL] [AL] Ask students what the current temperature in the classroom is. Ask them if all the objects in the room are at the same temperature. Once this is established, inquire them to identify their paw on their desk or on a metal object. Does it feel colder? Why? If their desk-bound is Formica laminate, and then it will feel cool to their hand considering the laminate is a good conductor of heat and draws heat from their hand creating a sensation of "cold" due to heat leaving the body.

Some materials only conduct thermal energy faster than others. In full general, metals (like copper, aluminum, gold, and silver) are good heat conductors, whereas materials like wood, plastic, and rubber are poor estrus conductors.

Figure 11.4 shows particles (either atoms or molecules) in two bodies at different temperatures. The (average) kinetic energy of a particle in the hot body is higher than in the colder body. If two particles collide, energy transfers from the particle with greater kinetic energy to the particle with less kinetic energy. When ii bodies are in contact, many particle collisions occur, resulting in a net flux of heat from the higher-temperature body to the lower-temperature body. The heat flux depends on the temperature divergence $\Delta T=T_{\text{hot}}-T_{\text{cold}}$ . Therefore, you will go a more astringent burn from boiling water than from hot tap water.

Figure 11.4 The particles in two bodies at different temperatures accept unlike average kinetic energies. Collisions occurring at the contact surface tend to transfer free energy from high-temperature regions to low-temperature regions. In this illustration, a particle in the lower-temperature region (correct side) has low kinetic energy before collision, but its kinetic free energy increases after colliding with the contact surface. In contrast, a particle in the college-temperature region (left side) has more kinetic free energy before collision, but its energy decreases afterwards colliding with the contact surface.

Convection is heat transfer by the movement of a fluid. This type of rut transfer happens, for example, in a pot humid on the stove, or in thunderstorms, where hot air rises up to the base of the clouds.

Tips For Success

In everyday language, the term fluid is commonly taken to hateful liquid. For example, when you are sick and the physician tells you lot to "button fluids," that but means to drink more beverages—non to breath more air. Nevertheless, in physics, fluid ways a liquid or a gas. Fluids movement differently than solid textile, and fifty-fifty have their own branch of physics, known equally fluid dynamics, that studies how they motion.

As the temperature of fluids increase, they aggrandize and become less dumbo. For instance, Figure 11.4 could correspond the wall of a airship with unlike temperature gases inside the balloon than outside in the surroundings. The hotter and thus faster moving gas particles within the airship strike the surface with more than force than the cooler air exterior, causing the balloon to expand. This decrease in density relative to its environment creates buoyancy (the trend to rise). Convection is driven by buoyancy—hot air rises considering it is less dense than the surrounding air.

Sometimes, we command the temperature of our homes or ourselves by controlling air movement. Sealing leaks around doors with atmospheric condition stripping keeps out the common cold wind in winter. The business firm in Effigy 11.5 and the pot of h2o on the stove in Figure 11.6 are both examples of convection and buoyancy past human pattern. Bounding main currents and large-calibration atmospheric circulation transfer energy from one part of the world to another, and are examples of natural convection.

Figure eleven.5 Air heated past the so-called gravity furnace expands and rises, forming a convective loop that transfers energy to other parts of the room. As the air is cooled at the ceiling and exterior walls, it contracts, eventually condign denser than room air and sinking to the floor. A properly designed heating system like this one, which uses natural convection, can be quite efficient in uniformly heating a home.

Figure 11.six Convection plays an important role in heat transfer inside this pot of water. Once conducted to the inside fluid, heat transfer to other parts of the pot is mostly by convection. The hotter water expands, decreases in density, and rises to transfer heat to other regions of the h2o, while colder water sinks to the bottom. This process repeats as long every bit in that location is water in the pot.

Radiation is a form of heat transfer that occurs when electromagnetic radiation is emitted or absorbed. Electromagnetic radiations includes radio waves, microwaves, infrared radiation, visible low-cal, ultraviolet radiations, X-rays, and gamma rays, all of which have different wavelengths and amounts of energy (shorter wavelengths have higher frequency and more energy).

Teacher Support

Teacher Support

[BL] [OL] Electromagnetic waves are as well often referred to as EM waves. We perceive EM waves of different frequencies differently. Just as we are able to see certain frequencies every bit visible light, we perceive certain others as heat.

You can feel the heat transfer from a fire and from the lord's day. Similarly, you tin can sometimes tell that the oven is hot without touching its door or looking inside—information technology may simply warm yous as y'all walk by. Some other example is thermal radiation from the human being torso; people are constantly emitting infrared radiation, which is non visible to the human eye, but is felt equally heat.

Radiations is the just method of estrus transfer where no medium is required, pregnant that the heat doesn't need to come into direct contact with or exist transported by whatsoever matter. The space between Earth and the sun is largely empty, without whatever possibility of heat transfer by convection or conduction. Instead, heat is transferred by radiation, and World is warmed as it absorbs electromagnetic radiation emitted past the lord's day.

Effigy eleven.7 Most of the estrus transfer from this fire to the observers is through infrared radiation. The visible light transfers relatively little thermal energy. Since peel is very sensitive to infrared radiations, y'all can sense the presence of a burn without looking at it directly. (Daniel X. O'Neil)

All objects absorb and emit electromagnetic radiation (run into Figure xi.seven). The charge per unit of estrus transfer by radiations depends mainly on the colour of the object. Black is the well-nigh effective absorber and radiator, and white is the least effective. People living in hot climates generally avert wearing black clothing, for case. Similarly, black asphalt in a parking lot will be hotter than adjacent patches of grass on a summertime day, considering blackness absorbs meliorate than green. The opposite is likewise true—blackness radiates better than dark-green. On a clear summertime night, the blackness asphalt will be colder than the green patch of grass, considering black radiates energy faster than green. In contrast, white is a poor absorber and also a poor radiator. A white object reflects well-nigh all radiation, like a mirror.

Teacher Support

Instructor Support

Inquire students to give examples of conduction, convection, and radiation.

Virtual Physics

Energy Forms and Changes

In this animation, you will explore estrus transfer with different materials. Experiment with heating and cooling the atomic number 26, brick, and h2o. This is done by dragging and dropping the object onto the pedestal and then holding the lever either to Heat or Cool. Elevate a thermometer abreast each object to measure its temperature—you can lookout how quickly information technology heats or cools in real fourth dimension.

Now allow'southward endeavour transferring heat betwixt objects. Heat the brick and so place information technology in the cool water. Now estrus the brick again, merely then place information technology on elevation of the atomic number 26. What exercise you find?

Selecting the fast frontward option lets you lot speed upwards the rut transfers, to save time.

Compare how apace the unlike materials are heated or cooled. Based on these results, what material exercise you lot think has the greatest specific oestrus? Why? Which has the smallest specific heat? Can you think of a real-globe situation where you would want to use an object with large specific heat?

1. Water will take the longest, and iron will accept the shortest time to heat, also as to absurd. Objects with greater specific heat would be desirable for insulation. For case, woolen clothes with large specific heat would prevent heat loss from the body.

2. Water volition accept the shortest, and fe will take the longest fourth dimension to oestrus, as well as to cool. Objects with greater specific heat would be desirable for insulation. For instance, woolen clothes with large specific heat would prevent heat loss from the torso.

3. Brick volition accept shortest and fe will have longest fourth dimension to heat up as well as to cool down. Objects with greater specific oestrus would be desirable for insulation. For instance, woolen clothes with large specific rut would forbid estrus loss from the body.

4. H2o volition accept shortest and brick volition accept longest fourth dimension to heat up as well as to absurd down. Objects with greater specific rut would be desirable for insulation. For example, woolen clothes with large specific rut would forbid estrus loss from the body.

Teacher Support

Teacher Support

Accept students consider the differences in the interactive exercise results if different materials were used. For instance, enquire them whether the temperature change would be greater or smaller if the brick were replaced with a block of iron with the same mass as the brick. Ask students to consider identical masses of the metals aluminum, aureate, and copper. Later on they have stated whether the temperature change is greater or less for each metallic, take them refer to Table 11.2 and check whether their predictions were correct.

Solving Heat Transfer Problems

Worked Example

Calculating the Required Heat: Heating Water in an Aluminum Pan

A 0.500 kg aluminum pan on a stove is used to oestrus 0.250 L of water from 20.0 $\text{°C}$ to 80.0 $\text{°C}$ . (a) How much oestrus is required? What per centum of the rut is used to raise the temperature of (b) the pan and (c) the water?

Strategy

The pan and the water are always at the same temperature. When yous put the pan on the stove, the temperature of the h2o and the pan is increased past the aforementioned amount. Nosotros employ the equation for heat transfer for the given temperature change and masses of h2o and aluminum. The specific oestrus values for water and aluminum are given in the previous table.

Give-and-take

In this example, most of the full estrus transferred is used to heat the water, even though the pan has twice every bit much mass. This is because the specific oestrus of water is over four times greater than the specific heat of aluminum. Therefore, it takes a bit more twice as much oestrus to attain the given temperature change for the h2o than for the aluminum pan.

H2o can blot a tremendous amount of energy with very little resulting temperature modify. This property of water allows for life on Globe because it stabilizes temperatures. Other planets are less habitable because wild temperature swings make for a harsh environment. You may take noticed that climates closer to large bodies of h2o, such as oceans, are milder than climates landlocked in the middle of a large continent. This is due to the climate-moderating issue of water'south big heat capacity—water stores large amounts of heat during hot weather and releases heat gradually when it's cold outside.

Worked Example

Calculating Temperature Increase: Truck Brakes Overheat on Downhill Runs

When a truck headed downhill brakes, the brakes must do work to convert the gravitational potential energy of the truck to internal energy of the brakes. This conversion prevents the gravitational potential free energy from being converted into kinetic energy of the truck, and keeps the truck from speeding upwardly and losing control. The increased internal energy of the brakes raises their temperature. When the colina is especially steep, the temperature increase may happen too quickly and cause the brakes to overheat.

Calculate the temperature increase of 100 kg of restriction material with an average specific heat of 800 J/kg $\cdot \text{°C}$ from a 10,000 kg truck descending 75.0 thousand (in vertical displacement) at a constant speed.

Strategy

We commencement calculate the gravitational potential energy (Mgh) of the truck, and then find the temperature increase produced in the brakes.

Discussion

This temperature is close to the humid indicate of water. If the truck had been traveling for some time, then just before the descent, the brake temperature would likely be college than the ambient temperature. The temperature increase in the descent would probable raise the temperature of the restriction material above the humid point of water, which would exist hard on the brakes. This is why truck drivers sometimes use a different technique for chosen "engine braking" to avoid called-for their brakes during steep descents. Engine braking is using the slowing forces of an engine in low gear rather than brakes to slow downwardly.

Practise Problems

five .

How much rut does it have to raise the temperature of 10.0 kg of h2o past one.0 °C ?

1. 84 J
2. 42 J
3. 84 kJ
4. 42 kJ

6 .

Summate the change in temperature of 1.0 kg of h2o that is initially at room temperature if 3.0 kJ of heat is added.

1. 358 °C
2. 716 °C
3. 0.36 °C
4. 0.72 °C

Bank check Your Agreement

Teacher Support

Teacher Support

Use these questions to assess student achievement of the section's learning objectives. If students are struggling with a specific objective, these questions will help identify which and direct students to the relevant content.

7 .

What causes heat transfer?

1. The mass departure between two objects causes heat transfer.

2. The density departure between two objects causes heat transfer.

3. The temperature divergence betwixt two systems causes estrus transfer.

4. The pressure level difference betwixt ii objects causes heat transfer.

8 .

When ii bodies of dissimilar temperatures are in contact, what is the overall direction of heat transfer?

1. The overall direction of oestrus transfer is from the higher-temperature object to the lower-temperature object.

2. The overall direction of heat transfer is from the lower-temperature object to the college-temperature object.

3. The direction of heat transfer is get-go from the lower-temperature object to the college-temperature object, so dorsum again to the lower-temperature object, and then-forth, until the objects are in thermal equilibrium.

4. The direction of oestrus transfer is offset from the higher-temperature object to the lower-temperature object, then dorsum again to the higher-temperature object, and so-forth, until the objects are in thermal equilibrium.

ix .

What are the dissimilar methods of heat transfer?

1. conduction, radiation, and reflection

2. conduction, reflection, and convection

3. convection, radiation, and reflection

4. conduction, radiation, and convection

10 .

Truthful or simulated—Conduction and convection cannot happen simultaneously

1. True
2. False

Source: https://openstax.org/books/physics/pages/11-2-heat-specific-heat-and-heat-transfer

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