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# Electric current

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Electrical current

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### Electric current

1. 1. Chapter 23 Electric Current
2. 2. Flow of Charge • Charge flows when there is potential difference (voltage) • Analogy: water flows from high pressure to low pressure, as shown below, until equilibrium occurs • To continue water flow, a pump is needed
3. 3. Electric Current • Electric current = flow of electric charge • Meaning, the flow of electrons • What is the charge of an electron? – Answer: 1.60 × 10-19 coulombs • How many electrons would you need to have a charge of 1 coulomb? – Answer: 6.25 x 1018 electrons! • The rate at which electrons flow is measured in amperes, or amps for short • 1 amp = 1 coulomb / second (That’s a lot of electrons!) The bulb on this slide requires 2.4 amps!
4. 4. Voltage Sources • Batteries and electric generators remove negative charges from positively charged objects • The difference in charge results in the creation of a potential difference, measured in Volts • In the analogy below, the pump and battery create the potential difference • The valve and switch control the flow (on/off) • Water / Electrons flow from high pressure to low pressure
5. 5. Electrical Resistance • Voltage pushes charge. • To control how much charge flows, electrical resistance is applied to the flow • Consider a water hose – Resistance is less when the hose is shorter and… – Resistance is less when the hose is wider – Example: closing the end of the water hose controls how fast the water comes out • In electric currents – Resistance is less when the wire is shorter – Resistance is less when the wire is thicker • Electrical resistance is measured in Ohms, the symbol Ω • In drawings, it is represented by
6. 6. Ohm’s Law • Voltage = current x resistance (V = IR) • Voltage (volts), current (amperes), resistance (ohms) • Volts = amps / ohms Question 1. How much current will flow through a lamp that as a resistance of 60Ω when 12V are impressed across it? I = V/R = 12V/60Ω = 0.20A 2. What is the resistance of an electric frying pan that draws 12A when corrected to a 120V circuit? R = V/I = 120V/12A = 10Ω
7. 7. End of Part 1