One of the major effects of heat transfer is temperature change: heating increases the temperature while cooling decreases it. We assume that there is no phase change and that no work is done on or by the system. Experiments show that the transferred heat depends on three factors—the change in temperature, the mass of the system, and the substance and phase of the substance.
Figure 1. The heat Q transferred to cause a temperature change depends on the magnitude of the temperature change, the mass of the system, and the substance and phase involved. To double the temperature change of a mass m, you need to add twice the heat. To cause an equivalent temperature change in a doubled mass, you need to add twice the heat. The dependence on temperature change and mass are easily understood. Owing to the fact that the average kinetic energy of an atom or molecule is proportional to the absolute temperature, the internal energy of a system is proportional to the absolute temperature and the number of atoms or molecules.
Owing to the fact that the transferred heat is equal to the change in the internal energy, the heat is proportional to the mass of the substance and the temperature change. The transferred heat also depends on the substance so that, for example, the heat necessary to raise the temperature is less for alcohol than for water.
For the same substance, the transferred heat also depends on the phase gas, liquid, or solid. The symbol c stands for specific heat and depends on the material and phase. The specific heat is the amount of heat necessary to change the temperature of 1. Values of specific heat must generally be looked up in tables, because there is no simple way to calculate them.
In general, the specific heat also depends on the temperature. Table 1 lists representative values of specific heat for various substances. Except for gases, the temperature and volume dependence of the specific heat of most substances is weak.
We see from this table that the specific heat of water is five times that of glass and ten times that of iron, which means that it takes five times as much heat to raise the temperature of water the same amount as for glass and ten times as much heat to raise the temperature of water as for iron. In fact, water has one of the largest specific heats of any material, which is important for sustaining life on Earth. What percentage of the heat is used to raise the temperature of b the pan and c the water?
The pan and the water are always at the same temperature. When you put the pan on the stove, the temperature of the water and the pan is increased by the same amount. We use the equation for the heat transfer for the given temperature change and mass of water and aluminum. The specific heat values for water and aluminum are given in Table 1.
Because water is in thermal contact with the aluminum, the pan and the water are at the same temperature. Calculate the mass of water. Compare the percentage of heat going into the pan versus that going into the water. First, find the total transferred heat:.
In this example, the heat transferred to the container is a significant fraction of the total transferred heat. Although the mass of the pan is twice that of the water, the specific heat of water is over four times greater than that of aluminum. Therefore, it takes a bit more than twice the heat to achieve the given temperature change for the water as compared to the aluminum pan.
Figure 2. The smoking brakes on this truck are a visible evidence of the mechanical equivalent of heat. Truck brakes used to control speed on a downhill run do work, converting gravitational potential energy into increased internal energy higher temperature of the brake material. This conversion prevents the gravitational potential energy from being converted into kinetic energy of the truck.
The problem is that the mass of the truck is large compared with that of the brake material absorbing the energy, and the temperature increase may occur too fast for sufficient heat to transfer from the brakes to the environment.
Repeat Step 4 again once more and note the results. Then take another beaker and again half fill it with water. Then heat this water until 75 degrees Celsius and place the ball again within the water and repeat the previous steps like done for 45 degrees Celsius. This essay has been marked by a teacher! Sign up to view the whole essay and download a PDF with full teacher's notes.
Don't have an account yet? Create one now! Already have an account? Log in now! JavaScript seem to be disabled in your browser. You must have JavaScript enabled in your browser to utilize the functionality of this website. Join over 1. Page 1. Save View my saved documents Submit similar document. Share this Facebook. To investigate the factors which affect the rate of cooling of a hot object. Extracts from this document Introduction Aim To investigate the factors which affect the rate of cooling of a hot object.
Middle This is because a small volume of water will have fewer particles in. Conclusion I could have improved the investigation by increasing the amount of times I repeated each experiment. The above preview is unformatted text. Found what you're looking for? Here's what a teacher thought of this essay 4 star s.
Not the one? Search for your essay title Investigation to see the effect of temperature on the expansion of dough. Some materials simply conduct thermal energy faster than others. In general, metals like copper, aluminum, gold, and silver are good heat conductors, whereas materials like wood, plastic, and rubber are poor heat conductors.
Figure 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 two 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. Therefore, you will get a more severe burn from boiling water than from hot tap water.
Convection is heat transfer by the movement of a fluid. This type of heat transfer happens, for example, in a pot boiling on the stove, or in thunderstorms, where hot air rises up to the base of the clouds. In everyday language, the term fluid is usually taken to mean liquid. However, in physics, fluid means a liquid or a gas.
Fluids move differently than solid material, and even have their own branch of physics, known as fluid dynamics , that studies how they move. As the temperature of fluids increase, they expand and become less dense.
For example, Figure The hotter and thus faster moving gas particles inside the balloon strike the surface with more force than the cooler air outside, causing the balloon to expand. This decrease in density relative to its environment creates buoyancy the tendency to rise.
Convection is driven by buoyancy—hot air rises because it is less dense than the surrounding air. Sometimes, we control the temperature of our homes or ourselves by controlling air movement.
Sealing leaks around doors with weather stripping keeps out the cold wind in winter. The house in Figure Ocean currents and large-scale atmospheric circulation transfer energy from one part of the globe to another, and are examples of natural convection. Radiation is a form of heat transfer that occurs when electromagnetic radiation is emitted or absorbed. Electromagnetic radiation includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays, all of which have different wavelengths and amounts of energy shorter wavelengths have higher frequency and more energy.
We perceive EM waves of different frequencies differently. Just as we are able to see certain frequencies as visible light, we perceive certain others as heat. You can feel the heat transfer from a fire and from the sun. Similarly, you can sometimes tell that the oven is hot without touching its door or looking inside—it may just warm you as you walk by. Another example is thermal radiation from the human body; people are constantly emitting infrared radiation, which is not visible to the human eye, but is felt as heat.
The space between Earth and the sun is largely empty, without any possibility of heat transfer by convection or conduction. Instead, heat is transferred by radiation, and Earth is warmed as it absorbs electromagnetic radiation emitted by the sun. All objects absorb and emit electromagnetic radiation see Figure The rate of heat transfer by radiation depends mainly on the color of the object. Black is the most effective absorber and radiator, and white is the least effective.
People living in hot climates generally avoid wearing black clothing, for instance. Similarly, black asphalt in a parking lot will be hotter than adjacent patches of grass on a summer day, because black absorbs better than green.
The reverse is also true—black radiates better than green. On a clear summer night, the black asphalt will be colder than the green patch of grass, because black radiates energy faster than green. In contrast, white is a poor absorber and also a poor radiator. A white object reflects nearly all radiation, like a mirror.
Ask students to give examples of conduction, convection, and radiation. In this animation, you will explore heat transfer with different materials. Experiment with heating and cooling the iron, brick, and water. This is done by dragging and dropping the object onto the pedestal and then holding the lever either to Heat or Cool.
Drag a thermometer beside each object to measure its temperature—you can watch how quickly it heats or cools in real time. Heat the brick and then place it in the cool water. Now heat the brick again, but then place it on top of the iron. What do you notice? Selecting the fast forward option lets you speed up the heat transfers, to save time.
Have students consider the differences in the interactive exercise results if different materials were used. For example, ask 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, gold, and copper.
After they have stated whether the temperature change is greater or less for each metal, have them refer to Table What percentage of the heat is used to raise the temperature of b the pan and c the water? The pan and the water are always at the same temperature.
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