* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Sc9 - D 2.2 (teacher notes)
Survey
Document related concepts
Switched-mode power supply wikipedia , lookup
Lumped element model wikipedia , lookup
Operational amplifier wikipedia , lookup
Nanofluidic circuitry wikipedia , lookup
Negative resistance wikipedia , lookup
Surge protector wikipedia , lookup
Power MOSFET wikipedia , lookup
Electrical ballast wikipedia , lookup
Opto-isolator wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Current source wikipedia , lookup
Rectiverter wikipedia , lookup
Transcript
Learning outcomes: 1 I can calculate resistance using Ohm’s law. 2.2 Modeling and Measuring Electricity The flow of a Rocky Mountain River is used as a model to demonstrate electricity. Energy source: energy must come from somewhere and so must water. Energy comes from a battery or other, and water comes from glaciers. Resistance and current: Resistance in electricity is when the electrons encounter friction. In the river resistance is when the water smashes into rocks in rapids. Current: The more electrons used, the more powerful the current in a conductor. The more water in the river, the more powerful the current in the river. Unless there is a change in elevation, water doesn’t flow…it sits in a pool. It will only flow if it gains potential energy. (going down a hill) In electricity, electrons will not flow if there is no “pump” for the electrons. It will only flow if there is an electric potential. (voltage) We can use water in pipes, to demonstrate resistance and current. The size of the pipe determines the volume of water allowed through it. Thin and long pipe = lots of resistance, restricted flow. Large and short pipe = no resistance, lots of flow. o The amount of resistance, in a circuit, determines the size of the current. Need a computer - Activity #1: http://phet.colorado.edu/en/simulation/ohms-law Activity #2 : http://phet.colorado.edu/en/simulation/resistance-in-a-wire Ohms law proves a Mathematical link between VOLTAGE (V), CURRENT (I), and RESISTANCE (R). The unit of resistance was named after Georg Simon Ohm, the Ohm. Graph analysis 1. What is the subject? 2. What conclusion can be made with this graph? 3. What are the controlled variables? Manipulated? Responding? Ohm's Law states that as long as temperature stays the same: the resistance of a conductor stays constant, and the current is directly proportional to the voltage applied Using Ohms law: Quantity Symbol Ohm’s Law Unit Voltage Current Resistance V I R Volts (V) Amperes (A) Ohms (Ω) Calculated with Ohm’s law V=I *R I=V/R R=V/I Measured with Voltmeter Ammeter ohmeter Solving a Problem… An electric stove is connected to a 240 – V outlet. If the current flowing through the stove is 20 A, what is the resistance of the heating element? Steps to solving the Problem Information and Solution 1. Identify know quantities. Current (I) = 20 A, voltage (V) = 240 V 2. Identify the unknown quantity. Resistance (R) 3. Use the correct formula. R=V/I 4. Solve the problem. R=V/I R = 12 Ω = 240V / 20 A Practice Questions… 1. A 30-V battery creates a current through a 15 Ω resistor. How much current is created? 2. A motor has an internal resistance of 40 Ω. The motor is in a circuit with a current of 4.0 A. What is the voltage? 3. A current of 625 mA runs through a bulb that is connected to 120 V. What is the resistance of the bulb? 4. A bulb of 15 Ω resistance is in a circuit powered by a 3 V battery. What is the current in this circuit? 5. A bulb of 40 Ω resistance is in a circuit powered by a 3 V battery. What is the current in this circuit? 6. An electric heater draws 10 A from a 120 – V source. What is the heaters resistance? 7. A current of 1.5 A flows through a 30 Ω resistor that is connected across a battery. What is the battery’s voltage?