PHYSICS II - MIDTERM HOMEWORK A GROUP 12. What is the potential difference and electric potential? The effects of any charge distribution can be defined in terms of electric field or electric potential. Since the electrical potential is scalar, it is easier to use than the electric field, which is a vector field. We can define the electric field as the force per unit charge. Likewise, it is useful to define electrical potential (or simply potential) as the electrical potential energy per unit charge. By definition, the electric potential difference, or voltage, is the difference in electric potential between the final and the initial position when work is done upon a charge to change its potential energy. The electric potential is indicated by the V symbol. The positive test charge q in the electric field has electric potential energy Ua at point a. At this point, electric potential Va: Therefore, the potential difference (Vba) between points a and b will be equal to the following relation: Vba= Vb-Va = Ub-Ua q When a point charge q moves from point a to point b, we define the change in electrical potential energy ( Ub-Ua ) as the negative of the work done by the electrical force. The electrical potential and potential difference unit are given in joule / coulomb and volts respectively. So 1W = 1J / C. The potential difference is often called voltage. The potential difference Vba can be written as follows, since the difference in potential energy (Ub-Ua) is equal to the negative of the work Wba when the charge moves from point a to point b: Vba = Vb-Va = Ub-Ua = - Wba q q For example, consider two equally but opposite charged parallel plates and the distance between them is small relative to their width and height. The electric field will be smooth in most zones (Figure 2). Figure 2: Work done by the electric field in the movement of the positive test charge q from a to b 15. What are the Combinations of Capacitors? Explain - What is a Capacitor? Capacitors are two-ended circuit elements that store electrical energy as an electric field. Basically, it is obtained by placing an insulating material between two conductive plates. The letter C in the circuit and its equations and unit are represented by Farad (F). - What does a capacitor do? What is the duty? Capacitors do not transmit direct current (DC), but have the ability to transmit alternating current (AC). Thanks to these features, they are used for different purposes in most circuits. They are used for filtering in power supply circuits, generating the desired frequency in resonant circuits, and controlling the voltage and power flow in power transmission lines. - Structure of the Capacitor We have said that the capacitor can be created with an insulator located between two conductors. The insulating part may be empty or it may also be composed of a dielectric substance (paper, glass, plastic, ceramic, mica, etc.). - The Combinations of Capacitors Like all other two-prong circuit elements, capacitors can either be parallel or serially connected to electrical circuits. (i) Parallel combination of capacitors If multiple capacitors are connected in parallel, capacitance values are summed: (ii) Series combination of capacitors In case capacitors are connected in series, the inverse of the equivalent capacity by multiplication is equal to the sum of the inverse of each capacity value by multiplication: 18. What is superconductors , and give an exaple. When the temperature is low below a certain value, materials with zero direct current and electrical resistances are called superconductors. High conductivity or zero resistance allows infinite current to flow through the material. Hundreds of materials turn into superconductors at low temperatures. The properties of superconductors are not much different from those of metals. Superconductivity is the state of matter at a critical temperature or under a critical magnetic field. - Properties of Superconductor The superconducting materials show some amazing properties which are essential for current technology. The research on these properties is still going on to recognize and utilize these properties in various fields which are listed below: - Infinite Conductivity/ Zero Electric Resistance Meissner Effect Transition Temperature/Critical Temperature Critical Current Persistent Currents Super conductive materials can be made from more than 20 metallic elements. The 27 chemical elements, all metal, are superconductors in atmospheric pressure, in their own crystal-graphic forms. Commonly known among these are Aluminum, Tin, Lead, Mercury, Rhenium, Lanthanum and Proctantium. In addition, 11 elements that are metal and semiconductor like Uranium, Selenium, Cerium and Silicon are also super conductive under low heat and high pressure. Although bismuth is not a superconductor in its crystal graphic form, it can become a superconductor by going into a regular state at very low temperatures. None of the magnetic elements such as Chrome, Manganese, Iron, Cobalt and Nickel have superconductivity.