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Electricity Charged Objects: ◦ Electrostatics: the study of electrical charges that can be collected and held in one place. ◦ Static electricity: electricity caused by friction. Ex: Rubbing shoes on dry carpet. Electric Charge: ◦ Consider the following example… You place two pieces of tape next to each other onto a table. What happens when either is near my finger? What happens when both are near each other? What can you conclude about the charge on each object? Electric Charge: ◦ Consider another example… You place two pieces of tape onto a table, one on top of each other. What happens when either is near my finger? What happens when both are near each other? What can you conclude about the charge on each object? Electric Charge: ◦ Consider another example… You place two pieces of tape onto a table, one on top of each other. What general rules can you come up with to explain the observations you just made about both scenarios? Electric Charge: ◦ When concerning electrically charged substances, there are two rules that must be obeyed… Opposite charges attract. Like charges repel. Electric Charge: ◦ All matter is made of atoms, which consist of protons, neutrons, and electrons. Each of these subatomic particles has its own characteristic charge… Protons (+), neutrons (0), and electrons (-). While referencing specific content in the notes, explain how you determine the charge of a particle that has 13 protons, 22 neutrons, and 11 electrons. The term integer in math is defined as “a member of the set of positive whole numbers {1,2,3,…}, a member of the set of negative whole numbers {-1,-2,-3,…} and zero”. While referencing specific content in the notes AND the definition of integers provided above, propose an explanation as to why you should never expect to have a charged atom that is anything other than an integer. Electric Charge: ◦ All matter is made of atoms, which consist of protons, neutrons, and electrons. Each of these subatomic particles has its own characteristic charge… If the atom has more electrons than protons then the sample is negatively charged. Electric Charge: ◦ All matter is made of atoms, which consist of protons, neutrons, and electrons. Each of these subatomic particles has its own characteristic charge… If the atom has less electrons than protons then the sample is positively charged. Electric Charge: ◦ All matter is made of atoms, which consist of protons, neutrons, and electrons. Each of these subatomic particles has its own characteristic charge… Remember we can’t change the number of protons, only the number of electrons. Ions are atoms of various elements that are either positively or negatively charged. As we well know (or least should at this point), atoms gain or lose enough electrons so as to have the same number of electrons as the noble gas closest to it in terms of atomic number. This is the reason that the Ca atom will lose 2 electrons because it typically has 20 electrons where the noble gas closest to it, Ar, has 18 electrons. Now, while citing specific content in the passage above AND in your notes, identify whether the ion of Cl will be either negative or positive. Ions are atoms of various elements that are either positively or negatively charged. As we well know (or least should at this point), atoms gain or lose enough electrons so as to have the same number of electrons as the noble gas closest to it in terms of atomic number. This is the reason that the Ca atom will lose 2 electrons because it typically has 20 electrons where the noble gas closest to it, Ar, has 18 electrons. Now, while citing specific content in the passage above AND in your notes, identify why the charge of an ion of Al will be a +3. Conductors and Insulators: ◦ Electric current is the flow of electrical charge. ◦ Since electrons are much easier to remove from an atom than protons, then electric current is essentially the flow of electrons. Conductors and Insulators: ◦ Conductor: materials that very poorly restrict charge flow or electric current. Allow for relatively easy, free-flowing electrons. Examples of conductors… Metals. Conductors and Insulators: ◦ Insulator: materials that restrict charge flow or electric current. Examples of insulators… Wood, glass, silk, and plastics. Electric cords are constructed with copper wires coated in plastic to eliminate energy waste, promote safety from electrostatic discharge (shock), and reduce the potential for starting fire. The Electrostatic Force: ◦ Electrostatic force: the push or pull exerted on an object as a result of another’s charge. Can be either attractive or repulsive. Dependent on two variables… The size of the charge on both objects. The greater the charge the greater the electrostatic force. The Electrostatic Force: ◦ Electrostatic force: the push or pull exerted on an object as a result of another’s charge. Can be either attractive or repulsive. Dependent on two variables… The distance between the two objects. The greater the distance between the two objects, the smaller the force between them. While citing specific content found in the notes AND citing specific evidence found in the picture below, identify which case would result in the largest electrostatic attractive force. While citing specific content found in the notes AND citing specific evidence found in the picture below, identify which case would result in the largest electrostatic attractive force. The Electric Field: ◦ When dealing with charged objects, it is important to consider the hypothetical situation involving only one charged object. If there were only one charged object, would there be an electrostatic force exerted by the object? The answer lies in a theoretical concept called the electric field. The Electric Field: ◦ Electric field: a region of space around any charged body that predicts the affects of placing another charged object is placed in said space. To represent this field we employ the use of field lines. The Electric Field: ◦ Electric field: a region of space around any charged body that predicts the affects of placing another charged object in said space. The density of the lines, not length, indicates the relative strength of the field at that location. The Electric Field: ◦ Electric field: a region of space around any charged body that predicts the affects of placing another charged object is placed in said space. The greater the field strength the more the object placed in the field is affected. The greater the electrostatic force placed on it. The Electric Field: ◦ Electric field: a region of space around any charged body that predicts the affects of placing another charged object is placed in said space. For positive charges field lines radiate outward from the source producing the field. The Electric Field: ◦ Electric field: a region of space around any charged body that predicts the affects of placing another charged object is placed in said space. For negative charges field lines radiate inward toward the source producing the field. Draw the electric field for a +2.0 µC. ◦ What is the direction of the force applied onto a negatively charged object placed into the field? ◦ What is the direction of the force applied onto a positively charged object placed into the field? Draw the electric field for a +4.0 µC. Draw the electric field for a -2.0 µC. ◦ What is the direction of the force applied onto a negatively charged object placed into the field? ◦ What is the direction of the force applied onto a positively charged object placed into the field? ◦ So, what can you conclude about positively/negatively charged objects and the direction of force applied onto them? If I lift a box up in the air I am doing work onto it. “Work”, in the science sense can be defined as a force acting through a displacement (w = Fd). Because of this action of work, we are transferring potential (stored) energy to the box. ◦ The picture on the next slide illustrates a positively charged object creating an electric field and a negatively charged object that is pulled from location A to B. While referencing the passage above and the picture on the next slide, identify whether you believe that you can store electrical energy the same way that you can gravitational energy. Is it possible to store electrical energy if both objects were positively charged? Explain your rationale. Voltage and Current: ◦ Just like gravity, systems involving charged bodies also have a potential energy. Gravitational potential energy is defined as PE = mgh or PE = Fgh. Thus, the larger the weight force or distance between the object and the Earth the greater the potential energy of the object. Voltage and Current: ◦ Just like gravity, systems involving charged bodies also have a potential energy. Electrical potential energy: the energy stored in an electrical system as a result of its position and charge. Unlike gravitational potential energy, electric potential energy can be attractive and repulsive. Voltage and Current: ◦ Just like gravity, systems involving charged bodies also have a potential energy. Electrical potential energy: Unlike gravitational potential energy, electric potential energy can be attractive and repulsive. This makes electric potential energy somewhat different… Voltage and Current: ◦ Just like gravity, systems involving charged bodies also have a potential energy. Electrical potential energy: Consider the two following examples… Two unlike charges separated by a distance. So… Voltage and Current: ◦ Just like gravity, systems involving charged bodies also have a potential energy. Electrical potential energy: Consider the two following examples… Two like charges separated by a distance. So… While referencing specific content in your notes AND citing evidence found in the picture below, which of the following locations, “A” or “B”, will be of greatest electric potential? Hint…the object at either point is a negatively charged object. Which of the following cases will produce the greatest electric potential? Hint…in both cases the two charged objects are separated by an equal distance of “r”. Provide justification for your answer. Voltage and Current: ◦ Current (I): the flow of charge. Analogous to water flowing through a pipe. Measured in amperes or amps (A). Voltage and Current: ◦ Now, imagine a ball on a hill… Because it is at the top, it has potential energy. This means that work can be done onto it, which means that the ball will begin accelerating down the hill. This accumulation of speed will occur until the gravitational potential energy reaches a minimum. The same thing happens for electrical systems. Voltage and Current: ◦ Now, imagine a ball on a hill… This accumulation of speed will occur until the gravitational potential energy reaches a minimum. Just as the ball moves because there is a difference in gravitational potentials, charge, and thus current, will flow in electrical systems. This will always occur from high electric potential to low electric potential – same as gravitational potential energy. Voltage and Current: ◦ Now, imagine a ball on a hill… This will always occur from high electric potential to low electric potential – same as gravitational potential energy. This difference in electric potential energies is referred to as a potential difference (V). This is what drives current. Voltage and Current: ◦ Now, imagine a ball on a hill… This will always occur from high electric potential to low electric potential – same as gravitational potential energy. This difference in electric potential energies is referred to as a potential difference (V). Measured in volts (V). The picture below illustrates two metal spheres of differing charges. The outcome of touching these two spheres is also illustrated. As you can see electrons are moving from sphere 1 to sphere 2. As already defined in the notes, the movement of electrons is called current and is measured in amperes (A). While referencing electric potentials AND the picture below, explain why electrons move from sphere 1 to sphere 2. Voltage and Current: ◦ Electrical Resistance: Just as water encounters friction between itself and the pipe it is traveling through, current also encounters a special type of friction called resistance. Resistance: the slowing or restricting of charge flow. Created because not even metals are perfect conductors. Voltage and Current: ◦ Electrical Resistance: Just as water encounters friction between itself and the pipe it is traveling through, current also encounters a special type of friction called resistance. Resistance: the slowing or restricting of charge flow. Without resistance current would occur instantaneous and thus no potential difference would exist and thus no current. Voltage and Current: ◦ Electrical Resistance: Just as water encounters friction between itself and the pipe it is traveling through, current also encounters a special type of friction called resistance. Resistance: the slowing or restricting of charge flow. A resistor is a substance that has a specified amount of resistance. Voltage and Current: ◦ Electrical Resistance: Just as water encounters friction between itself and the pipe it is traveling through, current also encounters a special type of friction called resistance. Resistance: the slowing or restricting of charge flow. Measured in ohms (Ω). Voltage and Current: ◦ Electrical Resistance: Just as water encounters friction between itself and the pipe it is traveling through, current also encounters a special type of friction called resistance. Resistance: the slowing or restricting of charge flow. R = V/I As stated on page 6 of your notes, an electric potential difference (V) is “what drives electric current (I)”. The greater this potential difference in electric energies becomes, the greater the value of the current. While referencing the passage above AND specific evidence located on the graphs presented on the next slide, explain which graph is CORRECTLY illustrating the relationship between potential difference and current. An experiment is conducted by attaching a source of voltage through wires constructed of various materials. Current is measured and the results are presented on the graph located on the next slide. While citing specific evidence found in the graph on the next slide AND referencing your notes, identify through which material will the current encounter the most resistance. The Current Passing Through Various Materials as a Result of Varying Potential Differences 14.0 12.0 Material A Material B Current (I) 10.0 Material C Material D 8.0 6.0 4.0 2.0 0.0 0.0 2.0 4.0 6.0 Potential Difference (V) 8.0 10.0 12.0 As stated earlier in the notes, the term “resistance” is used to describe the frictionlike properties of a conductor. Essentially, resistance reduces electric current. While citing the passage above, explain how the equation below is an adequate mathematical description of electrical resistance. R = V/I Find the resistance of a portable lantern that uses 24 V power supply and draws a current of 0.80 A. The current in a handheld video game is 0.50 A. If the resistance of the game’s circuitry is 12 Ω, what is the voltage produced by the battery? A 1.5 V battery is connected to a small light bulb with a resistance of 3.5 Ω. What is the current in the bulb? Common resistors… What is the amount of resistance of the first four resistors found in the picture below? What are Circuits? ◦ A typical electrical circuit contains each of the following… Wires. A bulb or some other resistor. Source of emf (electromotive force). Example: battery, outlet, generator, etc. What are Circuits? Other circuit symbols… What are Circuits? ◦ Remember, in order for a continuous current to flow, an electric potential must be maintained at all times. This is why a closed-loop (continuous path from terminal to terminal) of wire and components must be used. An open-loop would lead to a build-up of charge in one location leading to a decrease in potential difference. Stops charge flow. Diagramming Circuits: 1. Draw the symbol for a source of Emf – usually a battery. Positive terminal on top. 2. Draw a wire coming out of the positive terminal. When you reach a resistor or other device, draw the symbol for it. Diagramming Circuits: 3. Place a junction “point” anywhere that there are two possible current paths. Place another where the paths reconnect. 4. Continue until you reach the negative terminal of the battery. Draw an electrical circuit that contains each of the components in order… ◦ 9.0 V battery, followed by a 30 Ω resistor, and finally followed by an open switch. Draw a diagram that contains a 6.0 V battery connected to a light bulb. ◦ Include in your diagram a voltmeter and an ammeter. Series and Parallel Circuits: ◦ Series: a single pathway for charge flow. You should be able to trace the path of charge flow with your finger without ever having to pick it up. Just like a garden hose, a series circuit will have the same current at any one location in the circuit. Series and Parallel Circuits: ◦ Series: a single pathway for charge flow. Because of V = IR and resistance being different for each component in a series circuit, the voltage across each component can be unique. These voltages however, will add up to the total the voltage of the battery. Series and Parallel Circuits: ◦ Series: a single pathway for charge flow. Since this circuit type offers only one pathway of charge flow, removing one component will result in a failure of the circuit. Results in an open-loop construction. Series and Parallel Circuits: ◦ Parallel: a circuit that offers multiple pathways of charge flow. You will NOT be able to trace the path of charge flow with your finger without ever having to pick it up. Operates more like a 3-way garden hose splitter than a single garden hose. Each path will have its own unique current based on resistance of the path. Series and Parallel Circuits: ◦ Parallel: a circuit that offers multiple pathways of charge flow. Operates more like a 3-way garden hose splitter than a single garden hose. The sum of all currents coming out of the pathways however, equal the total current coming into the circuit. Series and Parallel Circuits: ◦ Parallel: a circuit that offers multiple pathways of charge flow. Operates more like a 3-way garden hose splitter than a single garden hose. This splitting of current is the reason for lights dimming when turning on another device at home. Lights in series won’t dim because current isn’t split and thus reduced. Remember…P = IV and P = I2R. Series and Parallel Circuits: ◦ Parallel: a circuit that offers multiple pathways of charge flow. As a result of offering multiple paths for charge flow, this type of circuit construction allows for one or more components to be removed, yet allow for all other components to be functional. This is the reason why we can have multiple devises plugged into the same outlet. Series and Parallel Circuits: ◦ Parallel: a circuit that offers multiple pathways of charge flow. As a result of offering multiple paths for charge flow, this type of circuit construction allows for one component to be removed, yet allow for all other components to be functional. When you unplug one it doesn’t mean that all other devices fail. Series and Parallel Circuits: ◦ Parallel: a circuit that offers multiple pathways of charge flow. Even though each pathway may have its own current, the potential difference across each pathway is the same. Which of the following pictures below is in series? Parallel? Which of the following pictures below is in series? Parallel? Using the picture below, draw lines, which will represent wires, in such a fashion to put the bulbs in series. Parallel. Electric Power and Electrical Energy: ◦ Recall the ball and hill example… As the ball traveled down the hill (high gravitational potential energy to low gravitational potential energy), much of it’s potential energy is converted into kinetic energy. The same happens to electrical systems. Energy lost when the charge flows from high electric potential to low electric potential is converted into other forms, such as light, sound, or heat. Electric Power and Electrical Energy: ◦ Recall the ball and hill example… As the ball traveled down the hill (high gravitational potential energy to low gravitational potential energy), much of it’s potential energy is converted into kinetic energy. This is the reason why resistors heat as current travels through them. Electric Power and Electrical Energy: ◦ Recall the ball and hill example… As the ball traveled down the hill (high gravitational potential energy to low gravitational potential energy), much of it’s potential energy is converted into kinetic energy. The rate at which this electric energy is converted to some other form is… P = IV and P = I2R The Kilowatt-Hour: ◦ Energy companies vs. “power” companies. You pay for electrical energy usage not power. ◦ Kilowatt-hour (kWh): equal to 1000 watts delivered continuously for 3600 seconds. Fuses and Circuit Breakers: ◦ As you have already learned, as current meets a resistance, energy is pulled out of the electric circuit and converted into a different form like heat (P = I2R). Wiring, although conductor, does carry a small amount of resistance. So, when you plug too many devices into an outlet you increase the risk of fire. Fuses and Circuit Breakers: ◦ As you have already learned, as current meets a resistance energy is pulled out of the electric circuit and converted into a different form like heat (P = I2R). Wiring, although conductive, does carry a small amount of resistance. As a result, safeguards like fuses and circuit breakers are placed into home wiring to protect against electrical fires. Fuses and Circuit Breakers: ◦ Fuses: a devise consisting of a thin ribbon of wire with a low melting point. These are placed into the circuit so that if too much current is passing through the wires, the ribbon melts, creating an open-loop. Referred to as a “blown fuse”. Discontinues charge flow until fuse is replaced. Fuses and Circuit Breakers: ◦ Circuit breakers: a switch that opens a circuit automatically when the current exceeds a certain value. Meets newer electrical code. Are also used to prevent electrical fire. Resettable.