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Transcript
Schematic diagram: • A diagram of an electric circuit • Straight Lines Only! COPY THIS Schematic Diagrams Symbols: Battery Open Switch Resistor Closed Switch Bulb Types of Electric Circuits COPY THIS 2 types of electric circuits: Series Circuits and Parallel Circuits More than one path possible for electrons to flow A single path for electrons to flow Series Circuit Mini-Lab Make a circuit with two bulbs in series. Total resistance = sum of the individual resistances (light bulbs) on the circuit path. If one bulb burns out, the whole strand of lights won’t work! Done? Have a seat and continue to work on the reading assignment. 1 Mini-Lab Add a switch to your last circuit that can turn both bulbs on and off. Done? Have a seat and continue to work on the reading assignment. Parallel Circuit Mini-Lab Make a circuit with two bulbs in parallel. On a warm up paper, draw a schematic of this circuit. Done? Have a seat and continue to work on the reading assignment. Mini-Lab Add a switch to your last circuit that can turn one bulb on and off without affecting the other. Done? Have a seat and continue to work on the reading assignment. Mini-Lab END Add another switch to your last circuit so that the other bulb can be turned on and off also, without affecting the other. s Done? Have a seat and continue to work on the reading assignment. 2 An Analogy for a Circuit: Voltage, Current and Resistance COPY THIS VOLTAGE (V) is ELECTRICAL POTENTIAL ENERGY and is measured in VOLTS (V) What is Voltage? Voltage is like “pressure” that pushes charge through the circuit. Voltage is a kind of potential energy (stored energy) The metric unit used to measure voltage is volt (V). Voltage can describe the energy stored in batteries: Low Voltage (Low Potential Difference) High Voltage (High Potential Difference) 3 Anatomy of a Battery About Batteries: Positive Terminal Zinc Anode (-) How does a battery work? Electrons collect on the negative terminal of the battery. If you connect a Graphite Cathode (+) wire between the negative and positive terminals, the electrons will flow from Chemical Paste (makes the electrons) the negative to the positive terminal as fast as they can. Negative Terminal About Batteries: Where does a battery get its electrons? COPY THIS CURRENT (I) Inside the battery itself, a chemical reaction produces the electrons. The speed of electron production by this chemical reaction controls how many electrons can flow between the terminals. CURRENT (I) measures the flow of charge 1 AMP of Current means 6,250,000,000,000,000,000 electrons per second!! ELECTRIC CURRENT is the FLOW of electrons, measured in AMPERES (A) What is Current (I)? Current is the flow of electrons through the circuit. Current is measured in electrons per second, called amperes. The metric unit used to measured current is amperes (A) 4 COPY THIS What’s difference between… Current I Voltage V (in Amperes) (in Volts) RESISTANCE R you could say that… Volts measure the pressure in the hose. ELECTRICAL RESISTANCE slows down the current and is measured in OHMS () Amps measure how much water comes out of a hose per second. What is Resistance? Resistance Resistance controls the amount of current in a circuit. Think of water flowing through a pipe. A narrow pipe has more resistance because of it slows the flow of water through the pipe. The greater the resistance, the less current gets through. •The metric unit for measuring resistance is the Ohm ( ) Conductors vs. Insulators •Conductors – material through which electric current flows easily; they have low resistance. Insulators – materials through which electric current cannot move; they are resistors. COPY THIS Ohm’s Law V = IR Relates: Voltage (V) in volts (V) V I R V = IR Current (I) in amperes (A) I = V/R Resistance (R) in ohms () R = V/I 5 Examples Problem 1: A stove is connected to a 180-V outlet. If the heating element has a resistance of 18 calculate the current flowing through it. Formula: I=V R I = 180 V I = 10 A Given: V = 180 V I=? R = 18 Therefore, the current flowing through the stove is 10 A Examples Problem 3: If the resistance of fridge is 130 and the current is 0.845 A, what is the voltage? Given: V=? I = 0.845 A R = 130 Formula: V=IxR V = 0.845 A x 130 V = 109.85 V Examples Problem 2: In order to operate a hairdryer, the current required is 2.5 A. What is its resistance if the voltage supplied is 120 V? Formula: Given: V = 120 V I = 2.5 A R=? R=V I R = 120 V 2.5 A R = 48 Therefore, the resistance of the hairdryer is 48 Question # 1 A light bulb supplied with a voltage of 36 V has a 6 A current flowing through it. Calculate the resistance of the light bulb. Therefore, the voltage of the fridge is 109.85 V Question #2 Electric Power (P) COPY THIS A light bulb has a resistance of 3 . What is the current in the light bulb when a voltage of 12 V is supplied? POWER IS MEASURED IN WATTS 6 Electric Power Formula P=I/V Relates: I P V Voltage (V) in volts (V) P=I/V Current (I) in amperes (A) V=I/P Power (P) in watts (W) I = PV A schematic diagram is a special diagram that describes an electric circuit, using certain symbols to represent different devices in the circuit. This meter measures the amount of electric work done in the circuits, usually over a time period of a month. The work is measured in kWhr. COPY THIS Schematic Diagrams Symbols: Battery Open Switch Resistor Closed Switch Bulb Types of Electric Circuits COPY THIS Series Circuit 2 types of electric circuits: Series Circuits A single path for electrons to flow and Parallel Circuits More than one path possible for electrons to flow Total resistance = sum of the individual resistances (light bulbs) on the circuit path. If one bulb burns out, the whole strand of lights won’t work! 7 Parallel Circuit 8