Electricity - Electrical Principles and Technologies (Topics 1-3) PDF

Electricity! It’s Enlightening! Electrical Principles and Technologies Topic 1: Electric Charges  Electricity – Think About It What is electricity? Where does it come from? What do we use it for? How would your life be different without it?  RECALL Everyth...

Electricity! It’s Enlightening! Electrical Principles and Technologies Topic 1: Electric Charges  Electricity – Think About It What is electricity? Where does it come from? What do we use it for? How would your life be different without it?  RECALL Everything in the world is made up of atoms Each atom is made of smaller parts One of those parts is called an electron (negatively charged particle) What is Electricity? ⊹ A type of energy ⊹ Flow of electrons (When electrons move quickly from one atom to another it is called electricity) ⊹ Two types × Static: stationary, almost no movement of electrons × Current: continuous flow of electrons What is Electricity?  Producing Charges ⊹ We call materials that attract or repel other materials charged or carrying an electric charge. ⊹ Charges can be collected by: ⊹ rubbing materials together (tribocharging) ⊹ touching them together (tribocharging) ⊹ bringing them close together and then separated.  Static Electricity In many cases, charges produced by rubbing or touching remain stationary, so they are sometimes called static electricity. But these charges can move, so unbalanced charges is more accurate.  Static Electricity The quantity of electric charge is expressed in coulombs (C). A bright light bulb, for example, allows about 1 coulomb of electric charge to pass through it every second. Static Electricity Review Static electricity is the charge that stays on an object These charges are usually created through friction Charges can then jump from one object to another Examples of static electricity include static shocks, lightning  Electric Charges Benjamin Franklin (1706–1790) was the first to use the words “positive” and “negative” to describe charges. Franklin called the charge on amber that had been rubbed with fur negative. The charge left on the fur was called positive. Two different charges are called unlike charges. Two charges of the same type are called like charges.  Electric Charges From our Matter and Chemical Change unit, we know atoms contain positively charged particles (protons) and negatively charged particles (electrons). *Studying static electricity helps us understand what happens to electric charges at a subatomic level* Overall: Neutrally charged Negatively charged (-2) Positively charged (+3)  Law of Charges 1. Unlike charges attract 2. Like charges repel 3. Charged objects attract uncharged (neutral) objects RECAP FIND OUT Activity!  Neutralizing Unbalanced Charges ⊹ An electric discharge occurs as accumulated charges on a material is neutralized (became balanced). ⊹ Electric discharges can be harmless or incredibly dangerous because they can shock people, damage electronic equipment, and cause fires and explosions. ⊹ In a discharge, electrons either enter an object to make up for a shortage, or extra electrons leave the object.  Grounding ⊹ Connecting an object to Earth with a conducting wire— grounding the object—is an easy way to neutralize conductive materials. Earth is so large that it can easily supply enough electrons to neutralize a positively charged object. ⊹ Similarly, Earth can absorb extra electrons from a negatively charged object. Preventing Static Buildup ⊹ Charged objects attract dust and contaminants. They also stick together and jam equipment such as photocopiers. To decrease static buildup, anti-static sprays and coatings can be applied to carpets and other surfaces on which charge accumulates.  Preventing Static Buildup Electronic components like computer memory cards are especially sensitive to electrostatic discharge, so they are often shipped in special antistatic packaging. Before handling sensitive components, electronics technicians may fasten a “grounding strap” on their wrist. The strap contains conductive materials, so that when one end is grounded, any unbalanced charge on the technician’s hand or body is neutralized without harmful electric discharge.  Conductors and Insulators When a charge stays on the spot where you rub the object, that object is called an insulator. Insulators are materials that do Foil not allow charges to move freely on or Balloon through them. Materials that allow charges to move freely, are classified as conductors. Rubber Most metals are good conductors and mostBalloon non-metals are good insulators. Semiconductors Semiconductors Semiconductors are materials with higher conductivity than insulators but with lower conductivity than metals. Their conductivity is often increased by implanting foreign atoms into the otherwise pure material. In other words, making it impure by mixing in with a material that has free electrons DID YOU KNOW? Smartphones? Laptops? Gaming devices? Digital cameras? These familiar devices all rely on semiconductor technology! Semiconductors make up the "brains" of many of the electronic devices we use every day, but many people don't know what a semiconductor is. DID YOU KNOW? Semiconductors are special materials that can act as both conductors and insulators. Sometimes they conduct electricity, and sometimes they do not. Semiconductors allow us to make tiny electrical "switches" that can turn on and off. They control the flow of electricity in a device similar to the way a valve controls the flow of water from a faucet (We will learn more about this later). Semiconductors control the flow of electricity in a device. In this way, they are like traffic controllers. They help devices work efficiently and reliably.  Superconductors Superconductors are materials that offer little, if any, resistance to the flow of charges. Certain materials become superconductors when they are extremely cold (about –137.15oC to –273.15oC). Superconductors are usually made of lead/mercury, metal alloys (niobium–titanium, germanium–niobium, and niobium nitride) and ceramics. Some applications of superconductors include components for electric generators, high-voltage power lines, and supercomputers. Superconductors Superconductors take up less space and can carry higher charges than ordinary conductors. In one power transmission application, about 114 kg of superconducting wire replaced about 8200 kg of copper cable, making it more than 7000% more space efficient. Read pgs & complete Practice Questions: 1. List the three “Laws of Charges.” For each law, give an example of the law being applied. 2. Describe the difference between a negatively charged object and a positively charged object. 3. Why is the phrase “unbalanced charges” a more accurate way of describing the phenomena we often refer to as “static electricity”? 4. How do conductors and insulators differ from each other? Electrical Principles and Technologies Topic 2: Electricity Within a Circuit Current Electricity Type of electricity used in our homes The steady flow of electricity is called an electric current A current will move along a wire or a path called a circuit Circuit means to “go around” Current Electric current is the amount of charge that passes a point in a conducting wire every second. The symbol for current is I. Electric current is measured in amperes (A) or milliamperes (mA) I t  Measuring Current An instrument used to measure very weak electric current is called a galvanometer. Larger currents are measured with an ammeter or milliammeter. The symbols for these instruments are a circle with “G,” “A,” or “mA” in the centre, respectively.  Voltage All forms of energy are measured in joules (J). However, when describing the energy of electrons in an electric circuit, we describe the energy possessed by a standard unit of charge instead of the total energy of all of the charges. The term potential difference means the difference in energy per unit of charge between one point in the circuit and another point in the circuit. Potential difference is commonly referred to as voltage. The standard unit for potential difference is the volt  Measuring Voltage Voltage is measured with a voltmeter. In circuit diagrams, the symbol for a voltmeter is a circle with “V” at the centre. Activity: Fill in the missing blanks Activity: Fill in the missing blanks Activity: Fill in the missing blanks  What is Resistance? Resistance is a property of a substance that hinders motion of electric charge and converts electrical energy into other forms of energy. When current flows through the high-resistance filament of the light bulb, the filament converts much of the energy of the current into light and heat. If the same current flows through a copper wire, you hardly notice it. Resistance, Voltage and Current If current is described as the movement of electrons through conductors, and voltage is what makes the electrons move, then resistance is what opposes the motion of the electrons.  Conduction and Resistance A good conductor has low resistance. (ex. copper) A poor conductor has high resistance. (ex. teflon)  Effect Factor Factor Then Resistance Length As Length Resistance Cross-sectional Area As Area Resistance (Gauge/Width) Temperature As Temp Resistance Material Due to the structure of their atoms, some metals allow electrons to move more freely than others Factors that Affect Resistance  Measuring Resistance The standard unit for resistance is the ohm, symbolized by the Greek letter omega (Ω). Resistance can be measured directly with an ohmmeter, but in practice, technicians are more likely to use a multi-purpose electronic measuring instrument (a “multimeter”) set to measure resistance.  Calculating Resistance: Ohm’s Law Electrical resistance is calculated by finding the ratio of the voltage across the load (V) to the current through the load (I). Ohm’s Law: Calculating Resistance: What is the resistance of a circuit across an electric hair dryer that uses 120 V when the current through it is 6.8 A? R = V/I R = 120 V/6.8 A R = 17.6 Ω “ Practice Calculating resistance Question on Page 12 Answers 1. 120 Volts 2. 240 Volts 3. 0.8 Amps 4. 0.13 Amps 5. 3.57 Ohms *(2 x 1.5V batteries = 3 V)* 6. 67 Ohms  Resistance, Voltage and Current: an Example with Numbers As the resistance in a circuit path increases, current decreases. Voltage(V) Resistance(Ω) Current (A) 10 1 10 10 2 5 10 5 2 Try it out! Read pages & complete Practice Questions: 1. What is electrical resistance? 2. Explain what it means when a material has low resistance? high resistance?Give an example of a material to use with low resistance and high resistance. 3. State Ohm’s Law. 4. What is the formula for resistance? Give the standard units for each quantity in it. 5. List three characteristics of a wire that increase electrical resistance. 6. What is the voltage across an electric water heater element that has a resistance of 32Ω when the current through it is 6.8 A? 7. Matt says that if the resistance to a load becomes larger, the current through it becomes larger as well. Angela says that if the resistance of a load becomes larger, the current will decrease. Do you agree with Matt or Angela? Explain your answer. Electrical Principles and Technologies Topic 3: Simple Circuits What is a Circuit? A circuit provides a continuous pathway for charges to move. A circuit must be closed for electricity to move.  Parts of an Electric Circuit Connecting Wire Copper wire Light Switch Switch Toaster AA battery Resistor or Load (2 or more cells) Battery Parts of an Electric Circuit 1 cell Light Bulb Voltmeter V Ammeter A Circuit Symbols ⊹ The cell symbol stands for a single cell. A battery is a combination of multiple cells. You can use a switch to “open” or “close” a circuit to control the current through it. The resistor symbol is used to represent one of many different loads. One load is used so much in laboratory work that it has its own symbol: the lamp. FYI: The Cell ⊹The cell stores chemical energy and transfers it to electrical energy when a circuit is connected ⊹When two or more cells are connected together we call this a battery ⊹The chemical energy inside a cell is carried by electrons from the negative terminal to the positive terminal and is used up as it pushes current around the circuit FYI: The Cell ⊹There are many different types of batteries depending on the application ⊹There are rechargeable batteries which can be used over and over again and one-use (disposable) batteries ⊹The chemistry inside the battery determines how many times it can be used and how long each charge will last  Circuit Elements Even the most complex circuits are made up of only four basic elements, or types of components.  Circuit Elements 1. Load: Items along the circuit that convert electricity into other forms of energy (eg. light bulbs, motors, heaters, and speakers). 2. Conductor: The wire through which current flows. 3. Source: The source of electric energy (eg. cell, battery) 4. Control: A switch or device that can turn the circuit or devices along it on or off.  Rivers of Electricity ⊹ Electric circuits are often compared to water systems. Electric charge flows through the parts of the circuit, just as water flows through pipes or along a river channel. The energy of the moving charge is changed to different forms as current passes through the load, just as the energy of moving water can be harnessed as it flows downhill. Identify the following points in each diagram on the next slide: (A) Where is the highest energy? Rivers of Electricity (B) Where is the lowest energy? (C) Identify the control (D) Locate the load (A) highest energy Rivers of Electricity (B) lowest energy A (C) control B (D) load C C B D A D  Drawing Circuits Circuit diagrams are drawn in a standard way to make them simple and easy to prepare and read. Your circuit diagrams should meet the following criteria for maximum marks.. Draw with a pencil and ruler on unlined pages OR graph paper Place components in a rectangular or square arrangement. Make conductors straight lines with right-angled ("square") corners. If possible, arrange your diagram so conductors do not cross. Draw neatly, making symbols a consistent size.  Try it Drawing Circuits out! Draw an electric circuit consisting of a battery made up of two 1.5 V cells, a switch, two lamps, and an ammeter in series. Indicate the direction in which the current flows. This is called a schematic circuit diagram  Try it Drawing Circuits out! Draw an electric circuit consisting of a battery made up of four 1.5 V cells, one switch, one lamp, two 0.50 Ω resistors in series, and a voltmeter. Indicate the direction in which the current flows. This is called a schematic circuit diagram  Resistors In electronic circuits, resistance is useful for more than changing the energy of moving charges into heat. One very common type of electronic component — the resistor — is used to control current or voltage to suit the specific needs of other electronic devices in the circuit.  Variable Resistors ⊹ Variable resistors do not have a fixed resistance, their resistance changes in response to temperature, light, voltage, or some other variable. ⊹ Variable resistors are used in a wide variety of electronic devices, from light dimmers and motor speed controls to surge protectors and refrigerator and stove temperature controls. Direction of the Flow of Electrons Electrons will always flow from the negative side of the battery through the wires of a circuit towards the positive end of the battery. Direction of the Flow of Current While electrons flow + - current from the negative electrons terminal to the positive terminal of a cell but current runs from positive to negative  Types of Circuits There are two types of electrical circuits; SERIES CIRCUITS PARALLEL CIRCUITS  Series Circuit ⊹ Series circuits have only one current path. ⊹ All the moving charges travel through each component in the circuit. ⊹ You can think of a series circuit as a set of parts connected end to end.  Series Circuit If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out  Parallel Circuits ⊹ Parallel circuits have several current paths. ⊹ The total current is divided, with some of the moving charges travelling through each branch, or part of the circuit.  Parallel Circuits The components are connected side by side The current has a choice of routes If one bulb ‘blows’ there is still a complete circuit so the other bulb will stays lit  Open vs. Closed Circuits A circuit can be described as either open or closed Closed circuit: the circuit is operating Closed – Light is and the current is flowing on I.e. The light switch is “on” and so are the lights. Open circuit: The circuit is NOT operating I.e. The light switch is “off” Open – Light is and so are the lights off House Wiring: Series vs Parallel Circuits ⊹ Practical electric circuits for the home are parallel circuits. The voltage across each load in a parallel circuit is the same. Turning on one appliance will not reduce the energy available to other loads. If you turn on too many appliances at the same time and the current increases too much, the wires could become hot enough to start a fire. To guard against an electrical fire, household circuits always include fuses or circuit breakers. Amazing energy facts to blow your mind!  Practice Questions 1. Match the water (hydraulic) related term from the column of terms on the right that best describes each electric term in the left column. (a) load (1) pump (b) switch (2) pressure (c) electric current (3) pipe (d) voltage (4) water wheel (e) battery (5) valve (f) conductor (wire) (6) flow rate 2. Draw a circuit diagram using symbols. Include a three celled battery, a switch, a lamp, an ammeter, and conducting wires. Make sure to add arrows to show the direction of the flow of electrons. 3. Describe the function of each part of the circuit in question 2. 4. Sketch circuit diagrams which show three light bulbs connected in: (a) series, and (b) parallel. 5. Give a reason for your answers below. Which type of circuit, series or parallel, will: a. have all bulbs turn off if one bulb is burnt out? b. produce the highest current through three bulbs? c. give brighter bulbs? 6. Draw a circuit that has a 2-celled battery, and a light that can be controlled at 2 locations (at the top/bottom of the stairs in your home, for example). 7. Explain why houses are wired in parallel. 8. Parallel circuits decrease the life of batteries. Why is this actually not a concern in houses? 9. Old fashioned Christmas tree lights were wired in series. Today, most Christmas tree lights are wired in parallel. Why do you suppose this is? 10. Complete the chart to tell about the factors that affect the resistance of wire. Complete review