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Transcript
Electrical The amountPotential of work that can be done by some charge moving in a circuit. Work electrical potential charge W V= q Joules units: = Volt = V Coulomb Current The movement of electrons through a conductor. The rate at which charge flows. charge current time I= q t Coulombs units: = Ampere = Amp = A Second DC (Direct Current) – All charges move in one direction in the circuit. AC (Alternating Current) – charges move one way and then the other, changing direction from moment to moment. CIRCUIT: A path where electrons flow and their energy is used. RESISTANCE: Opposition to the flow of electrons in a circuit. THE DAM ANALOGY Dam = Battery, Outlet, Power Supply Water Depth = V = Voltage or Potential Pipe = Wire Water Wheel = Energy User/Converter (Light Bulb, Motor…) Valve = Resistance or Current Control GROUND or Lowest Potential How can the resistance change? • What are the variables that effect the resistance of the flow of the water in the Dam Analogy? • Resistance is much like friction. The more “friction” against a current, the more resistance. First variable • What would happen if we widen the path for the water? • The resistance would be less. • Therefore: R is in proportion to 1/A 2nd variable • What would happen if we shorten the path of the valve? • There would be less to flow through, therefore the resistance would be less. • Therefore, R is proportional to L 3rd variable • What would happen if we thicken the walls of the pathway for the water? • There would be more resistance. • Therefore, R is proportional to density of the material. 4th variable • What would happen if we heat up the pathway of the water? • The resistance would increase • As resistance goes up, temperature goes up. Summary • 1) 2) 3) 4) Resistance of an object depends on Cross-sectional area of the resistor Length of the resistor Density of the resistor Temperature of the resistor What does the dam analogy tell us about the relationship between I and R? As R increases, I …… DECREASES! or How could the current be increased in a circuit whose resistance is held constant? Increase the “push” or VOLTAGE Georg Simon Ohm Ohm’s Law: V Voltage I UNITS FOR Current RESISTANCE Resistance R Volts Can Be Written As: Ohm More Typically Written As: Amp V V IR R This tells you the number of volts necessary to push 1 amp of current through the device. I OR Power • Deriving power of a circuit • P = Work/time • How is work related to potential of a circuit? PRACTICE PROBLEMS 1. If it took 5 minutes for 10 C to flow in a circuit, what was the current while the circuit was working? I = 0.033A 2. How long would it take for a 10 A stove top to pass 500 C of charge? t = 50 s PRACTICE PROBLEMS 3. What is the voltage on a circuit that has a resistance of 95Ω and a current flowing through it of 0.5 A? V = 47.5 V 4. What is the resistance of a circuit that is hooked up to a 12 V battery and has 0.02 A flowing through it? R = 600Ω