Physical Sciences, Part 20

Question 1: Discuss models for the flow of electric charge.

Answer 1: Models that can be used to explain the flow of electric current, potential, and circuits include water, gravity, and roller coasters. For example, just as gravity is a force and a mass can have a potential for energy based on its location, so can a charge within an electrical field. Just as a force is required to move an object uphill, a force is also required to move a charge from a low to high potential. Another example is water. Water does not flow when it is level. If it is lifted to a point and then placed on a downward path, it will flow. A roller coaster car requires work to be performed to transport it to a point where it has potential energy (the top of a hill). Once there, gravity provides the force for it to flow (move) downward. If either path is broken, the flow or movement stops or is not completed.

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Question 2: Briefly define power, watt, and transformer.

Answer 2: Power: Measured in watts, electric power refers to the rate at which electrical energy is transferred by an electric circuit. It can be calculated using Joule’s law: P = V*I, where “P” is power, “V” is the potential difference (in volts) and “I” is current (in amps). Power can be generated, transmitted, and converted into various forms of light.Watt: A watt is the unit used to measure power. One watt is equal to one joule of energy per second. Transformer: A transformer is a device that uses induction to transfer current from one circuit to another. Two wound coils act as a pair of inductors. Voltage can be modified to be transferred to another circuit (as in transmission lines) or to a load, such as an electrical device plugged into a socket.

Question 3: Compare and contrast direct and alternating current.

Answer 3: Direct current (DC) is the flow of an electric charge in one direction. Batteries and solar cells typically use direct current. Alternating current (AC) is current that periodically reverses direction. AC is typically used in houses and other buildings. A diode is an electronic device used to conduct electric current in one direction. The process of conduction in one direction is known as rectification. A rectifier is used to convert alternating current to direct current. Diodes are also used to remove modulation from radio signals. An inverter is the opposite of a rectifier in that it converts direct current to alternating current. Electromotive force (emf) is what causes electrons to move when there is potential difference between two points (voltage). Devices that can provide emf include batteries, voltaic cells, thermoelectric devices, solar cells, electrical generators, transformers, and Van de Graaff generators.

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