uggé: DC Circuits 2 Learning the Language for DC Circuits 2.1 Circuit Diagrams (a) circuit diagram is a representation that uses symbols to show the components in a circuit and how they are connected: Symbol Meaning battery light bulb switch oth sides switch is The short side must be drawn as indicates the connected Notes "open" in a positive end of for the circuit the battery bulb to diagram. light Symbols can be drawn in any orientation Wires connect at the points shown with X x (b) Use the symbols to draw a circuit for a battery, a light bulb, and a single wire. Make sure the diagram represents a circuit in which the bulb would light. x (c) Use the symbols to draw a DIFFERENT circuit diagram for a battery, a light bulb, and a single wire. Make sure the diagram represents a circuit in which the bulb would light. (d) Fill in the table below with some other symbols: Part of Circuit Sketch Schematic Symbol Notes (what does this element do?) Resistor mmeter Voltmeter Measures current through Measures potential difference across Ground Lesson activities adapted from LG and PUM, Etkina and Van Heuvelen, 2010
uggé: DC Circuits 2 2.2 Reason a. We learned that for a light bulb to glow, the two poles of a battery must be connected to the light bulb with conducting wires. Use you knowledge of the internal structure of conductors and understanding of the role of a battery to come up with analogies that can explain and predict phenomena related to electric circuits. fter you come up with your own analogies, examine two more analogies: one involving flowing water and the other involving a group of people running on a track. Remember that an analogy does not need to account for all aspects of a phenomenon. However, if you find similar aspects, make a note of them. Parts of the Electric Circuit attery Create your own analogy Parts of the water system analogy Parts of the running people system analogy Connecting wires Moving Electrons Light bulb, resistor b. Reason: Use the concept of potential difference to explain the role of a battery in a circuit. c. Describe an analogy between some part of a system with water flow in a pipe caused by a pump and the potential difference provided by a battery in a circuit. d. Describe an analogy between some part of a system with water flow in a pipe caused by a pump and the physical quantity electric current in a circuit. Lesson activities adapted from LG and PUM, Etkina and Van Heuvelen, 2010
uggé: DC Circuits 2 e. Use the flowing-water system, running-people system, and your own analogy to find analogies for the quantities potential difference and electric current. Fill in the table that follows. Electric Circuit Own analogy Water System Running People Potential difference between two points Current through wire f. Use the flowing-water system, running-people system, and your own analogy to find analogies for the quantities series circuit and parallel circuit. Fill in the table that follows. Observed Properties of the electric current When batteries are in series, the light bulb is brighter Own analogy Observed properties of the water system Observed properties of the running people system When identical batteries are in parallel, the lightbulb is the same brightness g. How can we explain the brightness of a light bulb using an energy explanation? Lesson activities adapted from LG and PUM, Etkina and Van Heuvelen, 2010
uggé: DC Circuits 2 2.3 Test your Ideas For each of the following circuits below; predict the brightness of the bulbs. Identify each circuit as series or parallel. Then, build the circuits using the PhET Circuit Construction Kit Simulation. re the results consistent with the predicted outcome? Explain the results using any of your analogies of electric phenomena. (a) (b) (c) (d) (e) 1 1 2 1 2 1 2 2 1 3 Circuit Prediction Results Explanation/Reconciliation a b c d e Lesson activities adapted from LG and PUM, Etkina and Van Heuvelen, 2010
uggé: DC Circuits 2 2.4 Reason (a) Consider the following partial circuit diagrams below, and indicate whether components between point and point are in parallel or in series: Consider the circuit drawn below, including batteries and and the three light bulbs: 1 2 3 (b) Indicate two sets of components that are each connected in series. (c) Indicate at least one set of components that are each connected in parallel. 2.5 Represent and Reason (a) Predict how the brightness of the top bulb shown in the illustration to the right changes when you close switch 1. 1 (b) Predict how the brightness of the top bulb changes when you close switch 2 (switch 1 is open). 2 (c) Rate the brightness of the three bulbs when both of the switches are closed. Explain your reasoning using any of the analogies. (d) Perform the experiment, record your observations, and compare them to your predictions. REFLECT: How would you explain to someone who did not study physics what the physical quantities electric current and potential difference describe. Why do we need both? Lesson activities adapted from LG and PUM, Etkina and Van Heuvelen, 2010
uggé: DC Circuits 2 Did You Know? Current: When there is a potential difference across a light bulb filament or just a wire in a closed circuit, the electrons in the wire move from lower potential to higher potential. However the conventional direction of the current is from high potential to low potential. You are probably asking why physicists came up with such an awkward convention. The answer is simple. We did not know any better. enjamin Franklin knew that some charged objects moved (he thought it was a fluid not particles), but he did not know if the fluid was positive or negative. With a fifty percent chance of getting it right he guessed wrong and we have been stuck with the convention ever since. We now know that not only do electrons move over the surface of the wire, but that the battery is not the source of electrons. The electrons that move through the circuit are the electrons that were initially in the wire (light bulb filament). These free electrons move randomly in all directions inside the wire that is not placed in external electric field. atteries create electric field (potential difference is one way to characterize that field) that adds some organized movement in a particular direction to the random motion of free electrons. They start drifting. Light ulbs: Filament of an incandescent light bulb lights up because it becomes very hot due to the current through it. s electrons move over the surface of the filament wire, they transfer kinetic energy to the ions of the filament through interactions with them. s the energy of particles in the wire increases, its temperature increases and it starts glowing. Lesson activities adapted from LG and PUM, Etkina and Van Heuvelen, 2010