Science Focus Topic 6 Notes: Transferring Energy | Print |
Energy can be transferred in three ways

Radiation Transfers Energy

Energy can be transferred even though there are no particles to transfer the energy.  This type of energy transfer is called radiation.  Radiation is the
transfer of energy without any movement of matter.  Energy that is transferred in this way is called radiant energy or electromagnetic radiation (EMR for short).
Radiant energy travels in waves (much like a tsunami). 

These waves can travel through space, air, glass and many other materials.  There are different forms of EMR, including radio waves, microwaves, visible light and X-rays. 

If the energy source is a warm object, like the sun, some of the thermal energy is transferred as a type of EMR called infrared radiation (IR) or 'heat radiation'.

Properties (characteristics) of Radiant Energy are:
Waves of radiant energy can travel in a vacuum.
All waves travel, across empty space, at an extremely high speed (300 Million m/s).
Radiant energy travels in a straight line.
they behave like waves
they can be absorbed and reflected by objects
All kinds of radiant energy interact with matter:
Reflection occurs if the energy cannot penetrate the surface of the material it comes into contact with.
Absorption occurs if the energy penetrates part way into the object.
Transmission occurs if the energy penetrates completely, passing through the object with no absorption of energy.

Absorbing / Emitting Energy

Dull dark objects absorb radiant energy when they are cool, and emit radiant energy when they are hot. (eg. asphalt sidewalk)
Light, shiny objects or surfaces do not absorb radiant energy readily and do not emit radiant energy readily. (eq. ice surface)
Radiant emission of energy from the body depends on surface area (smaller areas help to retain heat, whereas, larger areas radiate heat). This is evident in the adaptations of many species of animals who have successfully adapted to their environments.(desert animals - eg. Fox p. 140) (killer whales-The killer whale's fusiform body shape and reduced limb size decreases the amount of surface area exposed to the external environment. This helps killer whales conserve body heat.) The polar bear has black skin to absorb radiant energy with transparent hair that transmitts ultraviolet radiation to the skin.

Most radiation (82%) people are exposed, to comes from natural sources. By far the largest source is radon, an odorless, colorless gas given off by natural radium in the Earth's crust. Artificial radiation, mostly from medical uses and consumer products, accounts for about eighteen percent of our total exposure. The nuclear industry is responsible for less than one percent.

Radiation can be detected, measured and controlled.

The measurement of radiation is by the amount of radioactivity present
or the amount of radiant energy given off.

Radiation in the Environment

Radiation is a natural part of our environment. Humans have always lived on earth in the presence of radiation. Natural radiation reaches earth from outer space and continuously radiates from the rocks, soil, and water on the earth. Background radiation is that which is naturally and inevitably present in our environment. Levels of this can vary greatly. People living in granite areas or on mineraliscd sands receive more terrestrial radiation than others, while people living or working at high altitudes receive more cosmic radiation. A lot of our natural exposure is due to radon. a gas which seeps from the earth's crust and is present in the air we breathe.

Conduction, Energy Through Solids

In solids, where the particles are closely packed together, thermal energy can be transfered from one particle to another very easily. Thermal conduction is the process of transferring thermal energy by the direct collisions of the particles. The spaces between the particles, in different solids, determines how quickly these collisions can take place. Good conducting materials are those materials where there is little space between the particles - like most metals. Poor conductors, like glass and wood are called heat insulators. These insulators when wrapped around an object slow down the rate of thermal conduction.

Metals are good conductors of heat, so they are used extensively in cooking, because they transfer heat efficiently from the stove top or oven to the food.
Hot and cold packs are used to treat muscle injuries.

The Safety Lamp (The Davy Lamp) Davy invented his miner's safety helmet in 1815. The lamp of this safety helmet would burn safely and emit light even when there was an explosive mixture of methane and air present. Davy did not patent the lamp. (see explanation - Did You Know - p. 127)
The Radiator of a car transfers heat away from the engine, so that the gasoline being used will not ignite. (Antifreeze is used to achieve this)
The use of diamonds to transfer the heat generated by small electronic devices. Diamonds are called "ice" with good reason. Objects feel cold not only because they are at a lower temperature than our bodies, but also because they can transfer or conduct the heat away from us. When you touch a diamond to your lips, it feels ice-cold because it robs your lips of their heat. The capacity of a diamond to conduct heat distinguishes it readily from other gems and exceeds that of copper, an excellent thermal conductor, by about 4 times at room temperature. This exceptional property of diamond is increasingly being used for extracting heat from electronic devices to make them smaller and more powerful.
A Great Science Resource can be found at Science Net.

Convection, Energy on the Move

Thermal energy can be transferred by fluids in a third way, by the circular motion of the particles, called convection.

In convection, the warmer particles transfer their energy to the cooler particles as they move in a circular pattern, called a convection current. A simple experiment

Lava lamps are good examples to see this in action.

Birds and para-gliders make use of 'thermals' to help them soar and glide - helping them to conserve energy when they migrate.
Convection currents are also involved in creating the force of magnetism that surrounds the earth.
The convection oven is another of the many practical applications of convection.
The heat inside the oven, helps to provide uniform beating as the convection current transfers the heat evenly inside the oven.
Heating occurs through currents in a fluid, such as radiator water heating and flowing from the basement to heat a radiator on a floor above.

Analyzing Energy Transfer Systems

What happens when energy is transferred? The energy is not lost, it is only changed. Particles allow this transfer of energy to take place. The example of a Volleyball is given in the textbook on page 232.

Carrie's energy in her fist transferred to the ball, which transferred it to the floor. Conduction occurred, when the energy in her fist was conducted by the particles in her fist to the particles in the ball. The particles in the ball conducted the energy to the particles in the floor. The particles in the air were also warmed by the flight of the ball and the particles transferred this energy by convection currents which were created in the air.

Features of Energy Transfer Systems

All energy systems have five common features:

Energy Source - this is where the energy comes from that can be transferred throughout the energy system. The energy source can be mechanical, chemical, radiant, nuclear or electrical.
Direction of Energy Transfer - energy is always transferred away from the concentrated sources. Changes in non-living systems spread out the energy evenly.
Transformations - energy can change its form when it is transferred
Waste Heat - almost all of the energy is transferred directly from particle to particle, but some of the energy can be lost to the surroundings.
Control Systems - a control device can start and stop the transfer of energy (a thermostat in a home heating system)

Topic Review p. 236
Wrap-Up (Topics 4-6) p. 237