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Transcript
Topic 2 ELECTRICITY WITHIN A CIRCUIT Circuits • Electric circuits provide a continuous pathway. Circuit Elements and Diagrams Most complex circuits are made up of only four basic elements. • Source: The source of electric energy. • Conductor: The wire through which current flows. • Load: Items along the circuit that convert electricity into other forms of energy. • Control: A switch or device that can turn the circuit or devices along it on or off. • . Circuit Elements and Diagrams • A battery is a combination of cells. • You can use a switch to “open” or “close” a circuit to control the flow of current through it. • A resistor is used to represent one of many different loads. Measuring Current • Electric current is the amount of charge that passes a point in a conducting wire every second. • The symbol for the current is I. • Electric current is measured in amperes (A) or milliamperes (mA). Measuring Current • An instrument used to measure very weak electric current is called a galvanometer. Larger currents are measured with an ammeter of milliammeter. The symbols for these instruments are a circle with “G,” “A,” or “mA” in the center, respectively. Measuring Voltage • The energy for pushing electrons through comes from separated positive and negative charges. • In a battery, energy from chemical reactions does the work of separating the charges. • All forms of energy are measured in joules (J). Measuring Voltage • The energy of electrons in an electric circuit is described by a standard unit of charge instead of the total energy of all of the changes. Measuring Voltage • Potential difference means the difference in energy per unit of charge between one point in the circuit and another point in the circuit. • Potential difference is commonly referred to as voltage. – The standard unit for potential difference is the volt (V), named after Alessandro Volta (17451827), who built the first battery. Voltage is measured with a voltmeter; the symbol for a voltmeter is a circle with “V” at the centre. Current and Voltage • Electric current is equal throughout a circuit. • For the electric current to flow in a circuit, the battery must be supplying energy & there must be a continuous pathway for the electric current to travel. • Factors that affect the strength of an electric current in a circuit include the number of cells, voltage of the bulbs, type & length of the conductor, and the presence of loads. Current and Voltage • Batteries provide electrical energy. • Loads use electrical energy. • The energy provided to a circuit is very close to the energy used. • The voltage across individual loads adds up to a voltage very similar to the voltage across the entire load. • Voltage is higher when loads are removed because there is less resistance within the circuit. Rivers of Electricity • The load of an electrical circuit is comparable to a water wheel in a water system: – A switch is comparable to a valve – An electrical current is comparable to a flow rate – Voltage is comparable to pressure – A battery is comparable to a pump – A conductor (wire) is comparable to a pipe