# Electrical circuit

11. Oct 2016
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### Electrical circuit

• 2. 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.
• 3. 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)
• 4. 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.
• 5. 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.
• 6. TYPES OF VOLTAGE 1. 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
• 7. 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).
• 8. 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.
• 9. DEGREE OF RESISTANCE Conductors: 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.
• 11. NODES the electrical junction between two or more components CURRENT FLOWS Current 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).
• 12. 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
• 13. PARALLEL CIRCUITS • Components share two common nodes • Parallel components all have the same voltage drop across them
• 14. SERIES- PARALLEL CIRCUITCircuit is neither simple series nor simple parallel. Rather, it contains elements of both
• 15. Basic Ohm's Law Ohm’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, orV = A x Ω.
• 16. To find theVoltage, (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)
• 18. Example 1: Voltage (E) and resistance (R) are known
• 19. Example 2: Voltage (E) and current (I) are known
• 20. Example 3: Current (I) and resistance (R) are known. What is the voltage?
• 23. 1. If the circuit has a current of 2 amperes, and a resistance of 1 ohm, what is the voltage?
• 24. 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%.
• 25. ■ 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”)
• 27. 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%