9.2. Aluminum wires do have their drawbacks. It also protects the glass from the heat produced from the hot filament. What is the physical definition for this unit? Published under the terms and conditions of the Creative Commons Attribution License. This problem is another exercise in using scientific notation, and requires that students put concepts together that were learned previously. Legal. Explain what this other name for voltage means. Silver, gold, and aluminum are all used for making wires. Calculate the current an electric clothes dryer draws when it is connected to a 230 V source ands has a resistance of 9.2 Ω. In carbon, resistivity increases with the amount of impurities, meaning fewer free charges. Electric pressure 300+ TOP Current Electricity Multiple Choice Questions Answers CURRENT ELECTRICITY Multiple Choice Questions and Answers pdf,Interview Questions,mcqs,lab viva,seminar topics,online quiz important free download. DC is an acronym meaning Direct Current: that is, electrical current that moves in one direction only. \(\displaystyle T_c=37.0°C\) \(\displaystyle R=0.00302Ω\), 79. \(\displaystyle R=2.44×10^{−8}Ω⋅m(\frac{25m}{π(\frac{0.100×10^{−3}m}{2})^2})(1+0.0034°C^{−1}(150°C−20°C))R=112Ω\), 49. Technically, current’s mathematical definition involves calculus: However, students at this stage may not be ready to explore derivatives yet, and so the equation give in the answer for (average) current will suffice. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. The greater the resistivity, the higher the resistance. When beginning to explore the world of electricity and electronics, it is vital to start by understanding the basics of voltage, current, and resistance. R 200 ω v 240 v c i 15 a r. Voltage and current are proportional while the resistance remains constant. As mentioned above, the cost of the bulbs and the life span of the bulbs are important considerations. Do not allow students to simply give a “yes” or a “no” answer to either of the stated conditions. Air under normal conditions is a good insulator of electricity: that is, it possesses very high electrical resistance. Some electronics reference books use the letter “E” for voltage, while others use the letter “V”, or even use the two letters interchangeably. 9. Voltage: electrical “pressure” between two different points or locations. \(\displaystyle dR=\frac{ρ}{2πrL}dr\), \(\displaystyle R=\frac{ρ}{2πL}ln\frac{r_o}{r_i}\), b. Resistance: opposition, or "friction," to the flow of electrons. Conventional Current, Electric Field, Benjamin Franklin, and Electron Velocity (Doc Physics) Intro to Electrical Resistance, Resistors, and Resistivity (Doc Physics) Questions and Problems These are the questions and problems you'll be working on in class. Resistance :- Resistance of circuit is opposition offered to flow of current by that circuit. Increasing the resistance of an electric circuit will cause the current in the circuit to increase. In the case of static electric fields, the voltage between two points is equal to the electrical potential difference between those points. What are these units, and how do they relate to the unit of the volt? A very low resistance allows a large amount of current to flow. 9.1. Is it possible to have a condition where an electrical voltage exists, but no electric current exists? Stay the same. Device B shows a linear relationship and the device is ohmic. Solar cells can possibly be used to charge the batteries. ( R ) Resistance determines how much current will flow through a component. Notes: If students must master certain definitions, though, it is best to develop that mastery in the context of application: ask the students to use their new vocabulary, not just recite it. 33. a. Resistance: opposition, or “friction,” to the flow of electrons. Electrical resistance is an important factor in understanding the dynamics of electricity, and this quiz and worksheet combination will test how you've grasped this concept. It is important to realize that “DC” and “AC” may also be used to represent voltage as well as current. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. All four can easily be drawn into wires and have a high tensile strength, though not as high as copper. 9.2. In other words, use these three terms to explain the cycle of charge accumulation and lightning discharge. Since the drift velocity is inversely proportional to the cross-sectional area, the drift velocity in the 14-gauge wire is larger than the drift velocity in the 12-gauge wire carrying the same current. Encourage them to think of examples illustrating a possible condition. Even though electric motors are highly efficient 10–20% of the power consumed is wasted, not being used for doing useful work. \(\displaystyle P=\frac{W}{t},W=8.64J\), 81. [ "article:topic", "authorname:openstax", "license:ccby", "showtoc:no", "program:openstax" ], https://phys.libretexts.org/@app/auth/3/login?returnto=https%3A%2F%2Fphys.libretexts.org%2FBookshelves%2FUniversity_Physics%2FBook%253A_University_Physics_(OpenStax)%2FBook%253A_University_Physics_II_-_Thermodynamics%252C_Electricity%252C_and_Magnetism_(OpenStax)%2F09%253A_Current_and_Resistance%2F9.0A%253A_9.A%253A_Current_and_Resistance_(Answers), Creative Commons Attribution License (by 4.0), information contact us at info@libretexts.org, status page at https://status.libretexts.org. If you are attempting to maximize the resistance, the choice of the values for these variables will depend on the application. All four materials have a high conductivity, silver having the highest. The larger the difference between the outer radius and the inner radius, that is, the greater the ratio between the two, the greater the resistance. One of the more confusing aspects of electrical theory is that both voltage and resistance are quantities relative between two points. Lab 2: Resistance, Current, and Voltage I.Before you come to lab... A.Read the following chapters from the text (Giancoli): 1.Chapter 25, sections 1, 2, 3, 5 2.Chapter 26, sections 1, 2, 3 B.Read through this handout in its entirety. Don't have an AAC account? Gas molecules travel in completely random directions. It is caused by the accumulation of a large electrical charge over time resulting from air, dust, and water droplets transporting small electrical charges. It is not only possible, but quite common in fact, to have a condition of voltage with no current. Explain your answers, and give practical examples where the stated conditions are indeed possible. This question challenges students’ comprehension of voltage and current by asking them to explain the relationship between the two quantities in practical contexts. 1 ampere of electric current is the rate of electron motion equal to 1 coulomb per second: It may be helpful at this point to review the number of electrons constituting one coulomb of charge: 6.25 ×1018 electrons. A threefold increase in the resistance of an electric circuit will result in a threefold decrease in the electric current. Adopted a LibreTexts for your class? Notes: While it is easy enough for students to look up definitions for these words from any number of references, it is important that they be able to cast them into their own words. Section and Chapter Review 17-3 Supplementary activities. One way to combat this is to use two strain gauges, one used as a reference and the other used to measure the strain. 20 ELECTRIC CURRENT, RESISTANCE, AND OHM'S LAW Figure 20.1Electric energy in massive quantities is transmitted from this hydroelectric facility, the Srisailam power station located along the Krishna River in India, by the movement of charge—that is, by electric current. Aluminum has a higher rate of thermal expansion than copper, which can lead to loose connections and a possible fire hazard. \(\displaystyle R=ρ\frac{L}{A},ρ=2.44×10^{−}8Ω⋅m\), gold; \(\displaystyle R=ρ\frac{L}{A}(1+αΔT)\), b. In this regard, scientific method is a tool for the expansion of human ability. \(\displaystyle R_{copper}=23.77Ω\) \(\displaystyle P=2.377×10^5W\), \(\displaystyle 0.82R_0=R_0(1+α(T−T_0)), 0.82=1−0.06(T−37°C),T=40°C\). Describe what “electricity” is, in your own words. AC is an acronym meaning Alternating Current: that is, electrical current that periodically reverses direction (“alternates”). 8. These are the three basic building blocks required to manipulate and utilize electricity. Since the resistance is calculated as \(\displaystyle R=ρ\frac{L}{A}\), the resistance increases as the foil tracks are stretched. That is, it is possible to have a voltage that alternates back and forth in polarity (“AC” voltage) just as it is possible to have a current that alternates back and forth in direction of motion. Other materials may need liquid helium, which is even more costly. Electric current is measured in the unit of the ampere, or amp. Present day solar-powered cars are powered by solar panels, which may power an electric motor, instead of an internal combustion engine. Electrical resistivity is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. When an electric current flows through a bulb or any conductor, the conductor offers some obstruction to the current and this obstruction is known as electrical resistance and is denoted by R. Every material has an electrical resistance and this is the reason why conductors give out heat when current passes through it. 9.3. • • Define electric current electric current and electromotive force. Dissipating the heat would cool the filament, increasing the amount of energy needed to produce light from the filament. 3. This is because in general physics work, “E” usually stands for either “Energy” or “Electric field”. Special techniques must be used when using aluminum wires and components, such as electrical outlets, must be designed to accept aluminum wires. Using the flow analogy, electrical resistance is similar to friction. One of the liberating aspects of scientific investigation is that it frees us from the limitations of direct sense perception. a) 0.2 Ω. b) 0.5 Ω. c) 0.8 Ω. d) 1.0 Ω. 9.5. Explain how the terms voltage, current, and resistance relate to the process of lightning. At every point in time the current is equal to I(t)=V(t)/RI(t)=V(t)/R, so the current is also a function of time, \(\displaystyle I(t)=\frac{V_{max}}{R}sin(2πft)\). Collisions of moving charges with atoms and molecules in a substance transfer energy to the substance and limit current. 83. a. The electric property that impedes current (crudely similar to friction and air resistance) is called resistance R R size 12{R} {}. Suppose a battery outputs a voltage of 9 volts. The longer the length, the smaller the resistance. Explain what the electrical terms voltage, current, and resistance mean, using your own words. Explain electric current. If a wire is carrying a current, charges enter the wire from the voltage source’s positive terminal and leave at the negative terminal, so the total charge remains zero while the current flows through it. This work is licensed by OpenStax University Physics under a Creative Commons Attribution License (by 4.0). For example, CFL bulbs contain mercury, a neurotoxin, and must be disposed of as hazardous waste. If you’re having difficulty formulating a definition for “electricity,” a simple definition of “electric current” will suffice. However, when the voltage exceeds the air’s “ionization” potential, the air becomes a good conductor of electricity (its electrical resistance decreases dramatically), resulting in a transient current as the accumulated electric charge dissipates in the form of a lightning bolt. These three are related through Ohm’s Law. Some of your students may wonder later why the letter “I” is used to represent current. Using a high voltage reduces the current that is required to supply the power demand and that reduces line losses. \(\displaystyle R=\frac{ρ}{2πL}ln(\frac{R_0}{R_i})\); b. Through structured experimentation and rigorous thinking, we are able to “see” things that might otherwise be impossible to see. Voltage can be thought of as the pressure pushing charges along a conductor, while the electrical resistance of a conductor is a measure of how difficult it is to push the charges along. A threefold increase in the resistance of an electric circuit will result in a threefold decrease in the electric current. Voltage: electrical "pressure" between two different points or locations. Like all other physical quantities, there are units of measurement appropriate for specifying electrical quantities. Some materials require liquid nitrogen to cool them below their critical temperatures. When the original filaments were replaced with more efficient tungsten filaments, atoms from the tungsten would evaporate off the filament at such high temperatures. Current and resistance. of protons=\(\displaystyle 3.13×10^{16}\), 23. In an electric circuit, less resistance will pass a greater flow rate of electrons (current) for a given amount of ”pressure” (voltage). For example, why is it important to know that voltage is always a quantity existing between two points (rather than existing at a single point) when considering your personal safety? 21. a. In this sense, the “volt,” “amp,” or “ohm” are no different from “gram,” “yard,” or “bushel.”. This is quite different from the 5.55 ms for the truck battery. The time for 1.00 C of charge to flow would be \(\displaystyle Δt=\frac{ΔQ}{I}=\frac{1.00C}{0.300×10^{−3}C/s}=3.33×10^3s\), slightly less than an hour. The dimmer switches for LED lights are comparably priced to the incandescent light switches, but this is an initial cost which should be considered. Even though the electrons collide with atoms and other electrons in the wire, they travel from the negative terminal to the positive terminal, so they drift in one direction. Decrease. A miniature light bulb with a specific resistance is connected to a 1.5-Volt battery to form a circuit. If the Voltage stays the same and Resistance is increased, Current will . A miniature light bulb with a specific resistance is connected to a 1.5-Volt battery to form a circuit. answer choices . 11. Current: the flow of electrons. 18. \(\displaystyle P=\frac{V^2}{R},R=40Ω, A=2.08mm^2, ρ=100×10^{−8}Ω⋅m, R=ρ\frac{L}{A},L=83m\), 61. a. 7. \(\displaystyle R=R_0(1+αΔT),2=1+αΔT,ΔT=256.4°C,T=276.4°C\); b. The oxidation of aluminum does not conduct and can cause problems. In silicon and germanium, impurities decrease resistivity, meaning more free electrons. Though it may seem oxymoronic to refer to either “DC” or “AC” voltage (Direct Current voltage, or Alternating Current voltage - “current voltage”? Remembering a definition is not the same as really understanding it, and if a student is unable to describe the meaning of a term using their own words then they definitely do not understand it! Voltage is commonly defined as “electrical pressure.” The unit of the volt, however, may be defined in terms of more fundamental physical units. Using algebra, calculate how many joules of energy are imparted to every individual electron moving through this battery. 7. Current, on the other hand, is the coordinated motion of electric charge through a conductor. Yes, Ohm’s law is still valid. \(\displaystyle |J|=7.60×10^5\frac{A}{m^2}\); b. 15. He finds that the resistance between two points on the same finger is about the same as the resistance between two points on … The total current needed by all the appliances in the living room (a few lamps, a television, and your laptop) draw less current … Answers: 1 question Relationship of electrical power to current, voltage, and resistance • • Define resistivity of a material and apply formulas for its calculation. At first, these concepts can be difficult to understand because we cannot \"see\" them. X. It is also helpful to encourage students to give real-life examples of these terms. Electromotive force literally means, “a force that motivates electrons.”. 14. Under normal conditions, no it should not occur. The voltage between two points is a short name for the electrical force that would drive an electric current between those points. However, the existence of an electric current must normally be accompanied by a voltage. a) 1154 K. b) 1100 K. c) 1400 K. d) 1127 K. 13. Click here to let us know! The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. In the more general case with electric and magnetic fields that vary with time, the terms are no longer synonymous. As electric charges accumulate between clouds and earth, the voltage between these points increase. Electric Current and Resistance Question and Answer: 35+ Question with answer with explanation on electric current, resistor and resistance