electrical circuit
TRANSCRIPT
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CURRENT, RESISTANCE AND
VOLTAGE
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What is current?Current is the rate at which electrons flow past a point in a complete electrical circuit. At its most basic, current = flow.
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An ampere (AM-pir), or amp, is the international unit used for measuring current.
Amps are named for French mathematician/physicist Andrè-Marie Ampére (1775-1836)
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What is voltage?Voltage is the pressure from an electrical circuit’s power source that pushes charged electrons (current) through a conducting loop, enabling them to do work such as illuminating a light.
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In brief, voltage = pressure, and it is measured in volts (V). The term recognizes Italian physicist Alessandro Volta (1745-1827), inventor of the voltaic pile—the forerunner of today’s household battery.
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TYPES OF VOLTAGE1. Alternating current voltage
Commonly produced by utilities via generators, where mechanical energy—rotating motion powered by flowing water, steam, wind or heat—is converted to electrical energy
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2. Direct current voltage■ Travels in a straight line, and in one
direction only.■ Commonly produced by sources of stored
energy such as batteries.■ Sources of dc voltage have positive and
negative terminals. Terminals establish polarity in a circuit, and polarity can be used to determine if a circuit is dc or ac.
■ Commonly used in battery-powered portable equipment (autos, flashlights, cameras).
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What is resistance?
Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance. He is credited for formulating Ohm’s Law.
Resistance is a measure of the opposition to current flow in an electrical circuit.
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DEGREE OF RESISTANCEConductors: Materials that offer very little resistance where electrons can move easily. Examples: silver, copper, gold and aluminum.
Insulators: Materials that present high resistance and restrict the flow of electrons. Examples: Rubber, paper, glass, wood and plastic.
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ELECTRICAL CIRCUIT
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NODES the electrical junction between two or more components
CURRENT FLOWSCurrent flows from a high voltage to a lower voltage in a circuit. Some amount of current will flow through every path it can take to get to the point of lowest voltage (usually called ground).
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SERIES CIRCUITS
• There’s only one way for the current to flow in the above circuit
• Series components all have equal currents running through them
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PARALLEL CIRCUITS
• Components share two common nodes• Parallel components all have the same
voltage drop across them
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SERIES-PARALLEL CIRCUIT
Circuit is neither simple series nor simple parallel. Rather, it contains elements of both
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Basic Ohm's LawOhm’s Law is a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.To students of electronics, Ohm’s Law (E = IR) E = I x R
When spelled out, it means voltage = current x resistance, or volts = amps x ohms, or V = A x Ω.
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To find the Voltage, ( V )[ V = I x R ] V (volts) = I (amps) x R (Ω)
To find the Current, ( I )[ I = V ÷ R ] I (amps) = V (volts) ÷ R (Ω)To find the Resistance, ( R )[ R = V ÷ I ] R (Ω) = V (volts) ÷ I (amps)
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Example 1: Voltage (E) and resistance (R) are known
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Example 2: Voltage (E) and current (I) are known
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Example 3: Current (I) and resistance (R) are known. What is the voltage?
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1. If the circuit has a current of 2 amperes, and a resistance of 1 ohm, what is the voltage?
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RESISTOR COLOR CODING• The first and second
band represent the numerical value of the resistor,
• The color of the third band specify the power-of-ten multiplier.
If the band is gold, it specifies a 5% tolerance; silver specifies a 10% tolerance; if no band is present, the tolerance is 20%.
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■The colors brown, red, green, blue, and violet are used as tolerance codes on 5-band resistors only. All 5-band resistors use a colored tolerance band. The blank (20%) “band” is only used with the “4-band” code (3 colored bands + a blank “band”)
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Tolerance•Tolerance is the precision of the resistor and it is given as a percentage. For example a 390 resistor with a tolerance of ±10% will have a value within 10% of 390, between 390 - 39 = 351 and 390 + 39 = 429 (39 is 10% of 390).•BROWN: 1%•RED: 2%•GOLD: 5%•SILVER: 10%•NOTHING: 20%
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■THE END!!!