The Physics of Renewable Energy - Georgetown High School
Intro to Electricity and circuits pg. 45 Objectives Define electric current. Physics terms electric current
Identify the electric symbols for basic circuit elements. ampere (A) Use a multimeter to test continuity. open circuit
Identify and construct open, closed, and short circuits. electric circuit closed circuit short circuit Objectives
Physics terms Define voltage source. voltage resistance Characterize materials as conductors or insulators based on their electrical
properties. volt (V) resistor battery ohm ()
Demonstrate the use of multimeters, power supplies, and resistors. State and apply Ohms law to calculate current, voltage or resistance in an electric circuit involving a single resistor. Voltmeter electrical conductor electrical
insulator Important People in History Legend has it that Benjamin Franklin flew his metal key on his kite in a lightning storm & learned about what electricity was. Prior to 1800, no one knew how
to create a steady supply of electric current. Alessandro Volta was the first to succeed. He put two different metals in an acid or salt solution & produced an electric current between the terminals. He connected multiple voltaic piles together to create a battery of them.
What is electricity & how is it used Electricity is the flow of electric charges, typically through wires, conductors, and electrical devices. Sometimes we can see the effects of electricity in nature. Many household appliances and personal devices use electricity. The room you are in right now is
probably full of devices that use electricity. Key Terms in Electricity There are 3 key terms that well use throughout our discussion of electricity: Current Voltage Resistance
What is electric current? Electric current is the flow of charged particles, usually through wires and circuits. Current is measured in amperes or amps (A). Its symbol is I Animated illustration, page 472
Electric circuits & conserving charge An electric circuit is a conducting path through which electric current can flow. Electric current (I) must be the same at all points in a simple, single-loop circuit. Charge can never be created or destroyed. All the charge that flows through one point in the circuit must flow through the next point also.
Open and closed circuits An open circuit does not have a complete path so no current flows. A closed circuit has a complete path, allowing current to flow.
Common circuit elements What is a short circuit? What is a battery? A battery is a device that converts stored chemical energy into electrical energy. chemical energy
electrical energy Batteries come in many different kinds even lemons! Reading a battery Batteries come in many sizes and voltages: 1.5, 6, 9, 12 V, for example.
Voltage is the electric potential difference between the two terminals of a battery. Voltage is measured in volts (V), named after Volta, the inventor of the battery. Going further: Whats inside a battery How do you dispose of used batteries?
Batteries last for a long time, but what do you do when they are used up? Alkaline batteries: These batteries used to contain mercury, and so would have to be disposed with hazardous waste. Today, most alkaline batteries have no mercury and can be disposed in the trash. Do not pile many batteries together, however, because they can connect with each other and become hot! Rechargeable batteries: (nickel cadmium, lithium, car batteries, etc.) These must be recycled directly at a waste management center or through an auto dealer or home hardware store.
Volts and amps Current and voltage are the two most important physical quantities for understanding electric circuits. Current measures the flow of charge through a wire. Voltage measures the change in electrical potential energy per unit of charge. A useful analogy
Charges in a wire are analogous to water in a pipe: Electric current is analogous to the flow of the water. The battery is analogous to the water pump. Voltage is analogous to the change in gravitational Ep. Analogy: water and electricity Water flows because there is an energy difference, measured in height.
Current flows because there is an energy difference, measured in volts. View this short video on page 475 of your e-Book. Electrical conductors Electricity is all around us, yet we are not electrocuted
on a daily basis. Why not? Some materials are good electrical conductors, while others are good insulators. Air, plastic, glass, wood, and rubber are all good insulators. Electrical wire A typical electrical wire has copper on the inside and plastic insulation on the outside. Copper is a good
conductor because it has many electrons that are free to move through the material. The plastic covering on the wire protects us from getting electrocuted. Going further
Have you ever done any kind of wiring where you had to strip a wire? Why do you have to strip it in the first place? A small amount of plastic insulation must be removed from the ends of wires to use them in circuits. If your wires are not pre-stripped, then you will need to use a wire stripper to remove a small amount of the insulation. Water is conductive too!
Ordinary tap water may conduct electricity which is why you should never use electrical devices in or near a bathtub or shower! But also think about it, what is the cord to all your electronics made of? How much current?
This lamp conducts electricity. When the lamp is connected to a 10 V source, 2 amps of current flows through it. But why? What determines how much current will flow? The lamp itself helps determine the current flow. Is the lamp filament a good conductor, or does it resist the flow of current? Resistance
Some materials are better conductors than others. How do we quantify this difference? Electrical resistance (R) is a measure of how hard it is for electricity to flow through a material. Resistance is measured in ohms (). [ is the Greek letter Omega.] An ohm is a volt per amp Resistance: an analogy
Resistors Electric circuit elements that have resistance are called resistors. Resistors control the flow of current in a circuit. Light bulbs have resistance, too. Reading resistors
A resistor has three bands on one end, giving its value using two digits and a multiplication factor. How do we measure current, voltage & resistance? Electric current ammeter Voltage voltmeter Resistance ohmmeter More commonly we use a device that
can measure all of them, a multimeter. Equations Ohms law relates current to voltage and resistance in electrical circuits. Ohms law is not really a law: its a mathematical relationship closely obeyed by most conducting materials. Label what each stands for & their units. Three ways to use Ohms law
Write the equation (rearranged if necessary) that you would use to do each of the following. Determine the current through a resistor. Determine the voltage drop across a resistor. Determine the resistance of an unknown resistor.
Applying Ohms law What is the current through a 10 resistor when a voltage of 5 V is applied across it? 5 ohms Practice 1. What is the current through a 10 resistor when it is connected
to a 5 V battery? I = 0.5 amps 2. To reduce the current, should resistance be increased or decreased? increased 3. If the resistance increases by a factor of two, how does the current change? Current is half as much 4. What if resistance is halved? Current doubles 5. What is the voltage drop across a 50 resistor when a current of 0.10 A flows through it? 5.0 volts Homework
1.Which statement below is a correct definition of electric current? Electric current is . . . A. the energy of moving electrical charges. B. the flow of electric charges through a wire or circuit. C. the number of electrons in a circuit element. D. the attraction between charged particles in a wire. Homework 1.Which statement below is a correct definition of
electric current? Electric current is . . . A. the energy of moving electrical charges. B. the flow of electric charges through a wire or circuit. C. the number of electrons in a circuit element. D. the attraction between charged particles in a wire. Homework 2.Label each of these electrical symbols with the name of the electrical component it represents: battery;
resistor; lamp; switch; or wire. wire resistor lamp battery switch
Homework 3. Identify the following circuits: Short circuit Open circuit Closed circuit
Homework 4. Yuri connected his power supply (pictured below) to his circuit using the red plug. The lamp did not light. What did he do wrong? When using a power supply (voltage source) you must connect both the positive (red plug) and the negative (black plug).
Homework 5. Which statement below provides a correct practical definition of a voltage source? A voltage source . . . A. creates an electric potential difference between two points in a circuit, such as the two ends of a battery. B. provides the electrical potential energy needed for a circuit to operate. C. is analogous to the pump in a system of circulating water. D. all of the above.
Homework 5. Which statement below provides a correct practical definition of a voltage source? A voltage source . . . A. creates an electric potential difference between two points in a circuit, such as the two ends of a battery. B. provides the electrical potential energy needed for a circuit to operate. C. is analogous to the pump in a system of circulating water.
D. all of the above. Homework 6. What does the 1.5 V label on the battery mean? A.The voltage of the positive terminal is 1.5 V. B.The voltage of the negative terminal is 0 V. C.The voltage between the positive and negative terminals is 1.5 V.
D.All of the above Homework 6. What does the 1.5 V label on the battery mean? A. The voltage of the positive terminal is 1.5 V. B. The voltage of the negative terminal is 0 V. C. The voltage between the positive and negative terminals is 1.5 V. Voltage is a potential difference that is always measured between two points in a circuit.
D. All of the above Homework 7. Which materials listed below are conductors? a. aluminum b. rubber c. copper d. gold e. diamond
Homework 7. Which materials listed below are conductors? a. aluminum b. rubber c. copper d. gold e. diamond Homework 8. Which equation below is incorrect?
A. B. C. D. 9. What is the voltage drop across a 50 resistor when a current of 0.1 A flows through it?
10. What is the current through a 10 resistor when it is connected directly to a 15 V battery? Homework 8. Which equation below is incorrect? A. B. C.
D. 9. What is the voltage drop across a 50 resistor when a current of 0.1 A flows through it? 10. What is the current through a 10 resistor when it is connected directly to a 15 V battery?
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