V Current Electricity Introductory Physics Canadian AcademyGroup Members:
Current Electricity Construct and explain. Work in pairs or by yourself for these tasks. With each question: • Build it in the PhET simulation • Build it in the lab if possible • Draw the circuit diagram and answer the questions on the slide. You should be able to:http://phet.colorado.edu/en/simulation/ • Define current electricitycircuit-construction-kit-dc • Define resistance and state the factors that affect resistance in a metal wire • Define potential difference (voltage) Your finished work should be • Explain the effect of potential difference uploaded to SlideShare (or and resistance on a current Google Docs if it works) and • Draw basic circuit diagrams involving batteries, lamps, switches and wires embedded into a blog post. • Define electrical power including the relationship to voltage and current
Some basic circuit symbolsYou can use these to build the circuits on the next slides. wire cell battery junction + - + - cathode anode electron flow bulb/ lamp resistor conventional current What do these two components measure? switch V A voltmeter ammeter
A simple series circuit Build this circuit. Define current electricity. • A Label the direction of flow of electrons and the direction of the conventional current. What is the difference between them? Use the non-contact ammeter to measure the current in the circuit. • What happens if the cell is not included in the circuit? Explain. •
Switches and current Build this circuit. Measure the current with the switch in the open position. • A Close the switch and measure the current. Explain your answer. • Move the ammeter to different positions in the circuit and measure the current. Does position matter? • Are electrons ‘used up’ in the circuit? Are electrons ‘created’ in the cell?
Potential Difference (voltage) Modify the circuit to increase the potential difference by including two, then three, cells. What happens to the bulb? • Measure the current and potential difference. A Cells Current (A) Potential Difference (V) 1 2 3 Define potential difference (voltage). • V Complete the circuit diagram for three cells. Explain your results. •
Resistance (incandescent bulbs or lamps) Go to the following applet and see resistance at a molecular level and how a light bulb works. http://micro.magnet.fsu.edu/electromag/java/filamentr esistance/ Explain in your own words how moving charges cause a bulb to glow. What energy transfers and transformations are taking place? Explain what has happened when a cell (battery) has run out.
Resistance (incandescent bulbs or lamps) Build this circuit. Add bulbs and record your observations. Bulbs Current (A) Observations 1 2 A 3 4 5 Explain your findings in detail. Remove all the bulbs to create a short circuit and measure the current. Explain.
Conclusions Use your findings in the circuits so far to write your own Laws. Law of current in a loop. “ “ Law of voltage and current. (what’s the relationship?) “ “ Law of resistance and current. (what’s the relationship?) “ “ Why is it dangerous to have too little resistance in a circuit?
Arrange this equation based on your own observations. A = Ω VRIV potential difference resistance current 10
Arrange this equation based on your own observations. V potential difference I= RA current V Ω resistance 11
Parallel Circuits How many different routes can current take through this circuit? • Close the lower switch only. Observe the bulb and measure the current. • Close the upper switch only. Observe the bulb and measure the current. • Draw a circuit diagram for this set-up below: Close both switches. Observe the bulbs and measure the current at different positions. Observe the animation carefully. What happens to the electrons at junctions?
Law of Parallel Circuits Write your own Law, based on observations. Law of parallel circuits. “ “ Now test your Law using a third bulb in parallel. Draw the circuit diagram below and write your observations of the bulbs and of current.
More Parallel Circuits Close one switch at a time and record your observations. • Close both switches and record your observations. • Carefully observe the junctions. What is happening? Explain with reference to Draw a circuit diagram for resistance and junctions. this set-up below: • Do you need to modify your Law of Parallel Circuits?
Law of Parallel Circuits Modify your Law. Law of parallel circuits. “ “
More Resistance Use two cells and two bulbs in a circuit. Use CTRL-click to adjust the resistance of the bulbs (one is 20 ohms (Ω), the other is 10Ω). What is the difference between these two bulbs on a molecular level? • Wire up the bulbs in two different circuits: series and parallel. Draw the circuits below. Under each circuit, record and explain your observations. Series: Parallel:
Electrical Power Define electrical power and state its unit. • What is the relationship between electrical power and ‘power’ as we have studied in the previous unit? • Compare two methods of generating electrical power: one fossil-fuel based and one renewable. How do they work? What are the benefits/ disadvantages of each?
Extension If you finish with extra time: • Check the Laws you have written against published information. Do they concur? • Find out more about circuits and their components. • Find out about the difference between AC and DC. • Build your own circuits and draw the circuit diagrams below.
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