- Slides: 15
V Current Electricity Introductory Physics Canadian Academy Group Members: Daiki Kieran Kebin
Current Electricity Construct and explain. Work in pairs or by yourself for these tasks. With each question: • Build it in the Ph. ET 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 electricity • Define resistance and state the factors that circuit-construction-kit-dc affect resistance in a metal wire • Define potential difference (voltage) • Explain the effect of potential difference Your finished work should be and resistance on a current uploaded to Slide. Share (or • Draw basic circuit diagrams involving Google Docs if it works) and batteries, lamps, switches and wires embedded into a blog post. • Define electrical power including the relationship to voltage and current
Some basic circuit symbols You can use these to build the circuits on the next slides. battery cell wire junction + cathode bulb/ lamp anode + - electron flow resistor conventional current What do these two components measure? switch V A voltmeter ammeter
A simple series circuit Build this circuit. Define current electricity. • Is the flow of electrons 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. • It tells us the amount of amps. What happens if the cell is not included in the circuit? Explain. • There is no electrical current.
Switches and current Build this circuit. Measure the current with the switch in the open position. • 0 amps A Close the switch and measure the current. Explain your answer. • 0. 90 amps Move the ammeter to different positions in the circuit and measure the current. Does position matter? • Position doesn’t matter Are electrons ‘used up’ in the circuit? No, electrons are not used up. Are electrons ‘created’ in the cell? No, electrons are not created.
Potential Difference (voltage) Modify the circuit to increase the potential difference by including two, then three, cells. What happens to the bulb? • The bulb gets brighter Measure the current and potential difference. A V Complete the circuit diagram for three cells. Cells Current (A) Potential Difference (V) 1 0. 90 9. 00 2 1. 80 18. 00 3 2. 70 27. 00 Define potential difference (voltage). • the difference of electrical potential between two points. Explain your results. • The more batteries resulted a brighter bulb. • V= 10 A
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: The chemical within the battery runs out, not being able to move the electrons.
Resistance (incandescent bulbs or lamps) Build this circuit. Add bulbs and record your observations. A Bulbs Current (A) Observations 1 1. 80 2 0. 9 3 0. 6 4 0. 45 The bulb is very bright. The bulb has lost lots of brightness, every bulb you add the less bright it becomes 5 0. 36 Explain your findings in detail. Everytime you add a bulb, it loses brightness, this is because the energy is shared. In detail, the more bulbs there are, the more atoms the electrons run into. Remove all the bulbs to create a short circuit and measure the current. Explain. Everytime the distance of the wire increases, the amount of amps decreases, at the closest distance, there are 30, 000 amps. Also the battery caught fire.
Conclusions Use your findings in the circuits so far to write your own Laws. Law of current in a loop. “The current of electrons will always flow from the negative side to the positive side, in order for electrons to flow everything must be connected. “ Law of voltage and current. (what’s the relationship? ) “ The more batteries, the more voltage. If there is more voltage, there is more current. The shorter distance, the more voltage “ Law of resistance and current. (what’s the relationship? ) “ The more bulbs, the more resistance there will be “ Why is it dangerous to have too little resistance in a circuit?
Parallel Circuits How many different routes can current take through this circuit? • Three routes Close the lower switch only. Observe the bulb and measure the current. • Only the top bulb is powered. The electron flows through the outer part of the circuit Draw a circuit diagram for this set-up below: Close the upper switch only. Observe the bulb and measure the current. • Only the bottom bulb is powered. The electron flows through the bottom half of the circuit Close both switches. Observe the bulbs and measure the current at different positions. • The bulbs are not powered. The current has stopped Observe the animation carefully. What happens to the electrons at junctions? • The electrons split OR they are initially on top of each other, and they go towards different diresctions when they reach the junction.
Law of Parallel Circuits Write your own Law, based on observations. Law of parallel circuits. “ The total current flow in the circuit is equal to the sum of the current through all branches. “ 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. • One bulb is 1. 8 amps Close both switches and record your observations. • The energy is shared with the middle bulbs Draw a circuit diagram for this set-up below: Carefully observe the junctions. What is happening? Explain with reference to resistance and junctions. • Do you need to modify your 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.