Unit D Section 3.0 Devices and systems convert energy with varying efficiencies.
4.1 – Energy Forms and Transformations • Energy is the ability to do work • Common forms of Energy:
Chemical Energy is the energy found in chemicals, including food • Glucose is a common molecule used for the production of energy in humans • Chemical energy in the form of glucose can transformed to mechanical energy for movement
Thermocouples • A Thermocouple is a device that can convert Thermal energy to Electrical energy • Consists of two metals joined together that conduct heat at slightly different rates • When the metals heated, this difference in conduction results in electricity flowing from one metal to the other
The temperature affects the amount of electricity produced, so you can use a thermocouple as a thermometer • A thermocouple can be useful to ensure surfaces, like steel or other metals or metal alloys, are appropriately heated for machining, or to gauge when a container or location is too warm and coolants need to be introduced.
3.2 Energy Transformations involving Electrical and Mechanical Energy • Danish scientist, Hans Christian Oerstedconducted an experiment where he deflected a (magnetic) compass needle with a current carrying wire • He found that there is a relationship between electricity and magnetism
Faraday, constructed the first electric motor • He used electromagnetic forces to move an object • An Electromagnet is a coil of insulated wire (usually wrapped around a soft iron core) that becomes a magnet when current flows through it
How do you keep an electromagnet spinning in a magnetic field? The trick is to switch the direction that the current travels through the coil just as it aligns with the magnetic field of the permanent magnet. Reversing the current reverses the polarity (the north and south ends) of the electromagnet. It will then continue turning in order to align the opposite way. Changing the polarity of the electromagnet every half turn causes the electromagnet to be continuously pushed and pulled by the permanent magnet.
Electric Motors 3 Parts: • Commutator: is a split ring that breaks the flow of electricity for a moment and then reverses the connection of the coil • Stationary Magnetic Field • Armature: is the rotating shaft with coil wrapped around it
Polarity: A potential difference between two points of an electric circuit describing which of the two points has the higher electric potential
Direct Current: current that flows in only one direction • Symbol: DC • Devices that use it: • most devices that consume electricity -- cars, planes, light rail systems, computers, consumer electronics, and pretty much anything with a battery -- actually run on DC
Alternating Current: current that flows back and forth 60 times per second • Symbol: AC • Devices that use it: electricity in your household circuits • http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electricity/mainselecact.shtml
Transformers • device that changes electricity at one voltage into electricity at a different voltage • a step-up transformer increases the voltage • a stepdown transformer decreases the voltage
Generating Electricity • Michael Faraday demonstrated that electrical current could be generated by moving a conducting wire through a magnetic field • This is called Electromagnetic Induction • This discovery provided a way to generate a steady supply of large amounts of energy (A Generator)
One simple way to think about a generator is to imagine it acting like a pump pushing water through a pipe. Only instead of pushing water, a generator uses a magnet to push electrons along. A water pump moves a certain number of water molecules and applies a certain amount of pressure to them. In the same way, the magnet in a generator pushes a certain number of electrons along and applies a certain amount of "pressure" to the electrons.
Topic 3.3 Measuring Energy Input and output • Power: is the rate at which a device converts energy • Watt: is the unit of power (W) For an electrical device, the power is the current multiplied by the voltage. power (P), current (I), and voltage (V) is • P = I × V (watts = amperes × volts).
Power rating • The power rating of most small appliances in your home is: 1500 Watts or less • A stove might be 7000W • A calculator could be only 0.4W
Energy consumption • Energy consumption: the amount of energy a device uses • Recall that energy is measured in J - joules (watts × seconds). • The energy consumption of an electrical device is its input power multiplied by the time the device is used: E = P × t.
Kilowatt hours • Kilowatt hour: commonly used unit of electrical energy, equal to a power consumption of 1000 W for one hour • Electricity meters measure the energy used in kilowatt hours. The electric company then bills you for every kilowatt hour used. This cost can add up—a Canadian family's energy bill can be over $100 a month.
Law of conservation of energy • Law of conservation of energy: is the fundamental principle that energy cannot be created or destroyed • However, we usually find that the output energy of a device or system is smaller than the input energy, sometimes much smaller. • Most often, the missing energy is lost or dissipated as heat.
Efficiency • Efficiency: is the ratio of the useful energy output to the total energy input in a device or system; usually given as a percent
Comparing Efficiencies • fluorescent lights are about four times more efficient than incandescent lights. Although fluorescent tubes also produce more heat than light, they transform about 20% of their input energy into light. • Arc-discharge lamps are even more efficient. they produce light by passing an electric arc through a vapour of a metal such as mercury or sodium. Most cities use these high-efficiency lamps for streetlights.
Why reduce energy consumption? • Less electricity used = less money and reduces environmental impact
Improving Efficiency Increasing the efficiency of a device depends on its purpose • to decrease friction of moving parts as much as possible, you can use improved bearings and lubricants • Adding more insulation around the reduces the amount of heat escaping through the walls of the oven or the sides of the refrigerator