Thermal Energy Heat
Thermal (Heat) Energy Definition A form of energy that flows from one place to another because of a difference in temperature. II. Temperature A measure of how hot something is.
III. Absorbing Heat Increases the internal energy of a substance. i. Two types: kinetic energy of particles as they move within the substance. ii. potential energy of the particles that can be harnessed for use.
IV. Movement Heat flows from warm to cool areas and continues to flow until all areas have reached the same temperature.
Measuring Heat Energy A form of energy, so it is measured in Joules, like all other forms of energy.
Heat and Expansion As the temperature of a substance increases, the substance typically expands, as the particles that make up the substance push away from each other and vibrate more rapidly. Gases and liquids expand more than solids-their molecules have more energy.
II. Because solids expand at different rates, the difference can be measured. Bimetallic strip: when a strip of copper and iron are fixed together and, when heated, bends, as the copper expands more than the iron. III. Thermostats Use of bimetallic strips. They switch an electrical circuit on and off in response to changes in temperature.
Thermal Capacity Definition The amount of change in temperature to a substance when a specific amount of heat is added. Differs from substance to substance if the same amount of heat is added. Also called specific heat capacity.
II. Measured in degrees Celsius, degrees Fahrenheit, or according to the absolute temperature scale. Celsius: freezing is 0 and boiling is 100 Fahrenheit: freezing is 32 and boiling is 212
III. Absolute temperature scale Measured in kelvins (K), units that are the same size as degrees Celsius units Scale starts at Absolute Zero, equivalent to -273C, a point at which no further energy can be removed from a substance.
Thermometers An instrument for measuring temperature Liquid expands when heated, or Wire whose resistance changes with a change in temperature
Heat Transfer Convection: Main way for heat energy to be transferred in liquids and gases. As a substance heats, the part nearest the heat source expands and becomes less dense, causing it to rise. Movement is a convection current.
D. For example, the pattern of winds around Earth are caused by convection currents and become stronger as the Sun’s energy heats the Earth further.
II. Conduction Way in which heat energy in a solid is transferred. As energy nearest heat source increases, the particles vibrate more, spreading some of their energy and causing the heat to move through the substance.
C. Metals are good conductors because, not only do their particles vibrate, but also the freely moving electrons carry heat more quickly than do vibrating particles. D. Insulators are substances that conduct heat slowly, such as wood, water, and air. E. Other insulators include those materials that trap air, including wool, fur, and feathers.
III. Radiation Transfers energy in the form of electromagnetic waves. Does not depend on particle movement. The only form of energy that can move through a vacuum (a space completely empty of matter).
D. All radiation types, light included, cause things to heat up. E. Infrared radiation causes the greatest increase in temperature. i. are emitted by by the Sun and other hot objects. Dark-colored objects absorb radiation.
IV. Vacuum flasks A container for keeping liquids at a constant temperature. Two glass containers, one inside the other, have a vacuum between them. Vacuum prevents the transfer of heat by conduction or convection.