Charging and Discharging Capacitors and Capacitance - Essay Example

CHARGING AND DISCHARGING CAPACITORS AND CAPACITANCE + Submitted Charging and Discharging Capacitorsand Capacitance Capacitance is an aspect of Physics that is essential in our daily lives. The essay intends to exemplify the critique of two websites in terms of the way they each approach capacitance and capacitors. The two sources,are Advanced Physics for You by Keith Johnson, Simmone Hewett, Sue Holtand John Miller, and the MIT Open-source website (http://ocw.mit.edu/high-school/physics/demonstrations-on-video/conductors-capacitors-dielectrics/). According to Advanced Physics for You by Keith Johnson, Simmone Hewett, Sue Holt and John Miller, the approach of capacitance is from a simplified version. It states that a capacitor is described as a device that is passive in nature and is used for the purpose of storing up energy for use in its own electric field. Any item which can be charged electrically and store energy, can be assumed to be a capacitor. The authors reiterate that the capacitor comprises of two plates, which are usually separate from each other by the use of a dielectric. The two plates are good conductors of electricity and that is why they are separated by an insulator. A capacitor is used in the situation where huge amounts of charge are to be distributed within a short time. The book notes that a capacitor’s charge level depends on the amount of voltage that is applied to the capacitor. If the capacitor is connected to a battery that has high voltage, then more amounts of charge will be supplied to the capacitor’s conductors, as compared to when the capacitor is connected to a battery of a low voltage level. Capacitance is usually a function that does not depend on the difference in potential value between the conductors of the capacitor as well as the charge that is present on the plates. Capacitance can be compared directly to the overlap area created by the two conductor plates of the capacitor. On the other hand, it is inversely comparative to the distance of separation between the plates. Connection of capacitors can be done either in series or parallel in a circuit. The authors say that in some cases, an integration of the two arrangements can be incorporated. The amount of time taken to charge a capacitor relies on the size of the capacitor as well as that of the resistor in the electric circuit. Capacitance is usually measured in units known as the Farad abbreviated as F. one Farad is equivalent to one Coulomb/Volt which is abbreviated as F=C/V. the book states that the stored up energy in the capacitor is usually measured in units known as joules, and it is equivalent to the work that has been done during the charging of the capacitor. An MIT Open-source website (http://ocw.mit.edu/high-school/physics/demonstrations-on-video/conductors-capacitors-dielectrics/) however differs from the book in that it approaches capacitance from the mathematical point of view. It offers useful equations for calculating capacitance and manipulating charge. The source material reiterates that for the capacitors arranged in series, the capacitance is calculated using the following method: C =  1  +  1 + · · · +  1                  CS    C1     C2             Cn For the capacitors arranged in series, the capacitance is calculated using the following method: Cp = C1 + C2 + · · · + Cn A = Area of plates C = Capacitance (F) D = Distance between plates (m) a = Inner radius (m) b = Outer radius (m) q = Charge (Coulombs) x = Length (m) W = Energy (J) εr = Relative permittivity ε0 = 8.85 x 10-12 F/m D.F. = Dissipation Factor = 1/q The open-source document affirms that the capacitance of the figure below can be calculated by: On connecting a capacitor to a Direct Current (DC) circuit, charging as well as discharging of the capacitor will occur. The capacitor is first of all powered up by a DC power, and the current from the power supply flows throughout the capacitor’s circuit. The two plates in the capacitor acquire the same but opposite charges. This causes an increase in the difference of the potential value that comes as a result of the charging process of the capacitor. When the capacitor’s terminals acquire a voltage that equals to that of the power supply, then the capacitor becomes completely charged and the flow of the current in the circuit stops flowing. This then marks the end of the charging process of the capacitor which is usually a closed circuit. At this point, the capacitor becomes the same as an open circuit. On disconnecting the capacitor from the supply of power, the resistor in the capacitor then starts to discharge the capacitor. At the same time, the voltage level that is present between the two plates of the capacitor falls off in a gradual process until it goes to 0. The discharge rate of capacitors is usually exponential, given that time is kept constant. This implies that the charge of the capacitors drops at the same rate as the decay of the radioactive material. When it comes to radioactivity, half-life is used, and when it comes to the capacitance, a constant time is used. As time which is divided into equal intervals elapses (time constant), the charge of the capacitance drops equally for the time intervals. Advanced Physics for You considers a number of factors that affect capacitance in considerable details. The authors critically single out the following as the three factors that affect the capacitance of any capacitor. Foremost, the area of the plate determines to a great extent the amount of charge a capacitor stores. Keith et. al. note that the wider the area of the plate, the greater the amount of capacitance it exhibits. This is because a large area leads to an increase in the amount of field flux. The field flux is the amount of charge that is produced on the capacitor’s plates. With pictures illustrating proof in an experiment, the authors cite the space of the plates as the other factor that affects capacitance of a capacitor. The further apart the plates of the capacity are from each other, the lesser the amount of capacitance produced. The closely spaced the plates are, the amount of capacitance in the capacitor increases. When the plates are closely spaced, then the field force becomes greater. This then results to an augment in the amount of charge that is produced on the surface of the plates. The dielectric material is the last factor that the authors illustrate as affecting capacitance of a capacitor. The more permittivity produced by the dielectric material, the greater the level of capacitance produced, and the lesser permittivity the dielectric material provides, the lesser the amount of capacitance produced. This is because the dielectric material that offers more permittivity offers less resistance to the amount of field flux being produced on the plates. The molecules found in the dielectric material are of two charges, the positive and the negative charges. These two charges are usually separated from each other slightly. This makes the molecules in the material to be present in the electric field of the capacitor that is charged. Other than the formulae and the process of charging and discharging that MIT Open-source outlines in a convincing way, the materials outline factors that determine the rate of accumulation and drop of charge levels. It notes two factors that determine the rapid rate of the drop in the charge levels are; the amount of capacitance present in the capacitor, as well as the resistance at which the capacitor discharges through. In reality, it is approximated to take about 0.69*RC for the value of charge in the capacitor to reach half of the original value. At the same time, the discharge level of the current that is present drops off to half the original value as well. The difference in the potential value between the plates in the capacitor has a direct effect in the amount of charge that has been stored up in the plates (MIT Open-source, 2014). This is because the amount of charge stored is directly comparative to the difference of the potential value in between the plates. A capacitor with a relatively larger surface area and the two plates being positioned close to each other are said to have the ability to store up more charge. When the delay in the RC occurs, it prevents an increase in the speed of integrated circuits. The delay can be mitigated by making a replacement of the aluminum conducting material with a copper material. By doing this, the level of resistance in the capacitor will be reduced, hence decreasing the chances of experiencing a delay. Another method that that be used to reduce the delay is by changing the dielectric material which is usually made up of silicon dioxide, to a material that has a low-dielectric level, hence leading to a reduction in the level of the capacitance. Since the capacitors have the capability of storing up energy, they are well suited for use for the systems that are used for the purpose of back-up, for instance in the computers. Although Advanced Physics for You by Keith Johnson, Simmone Hewett, Sue Holt and John Miller and the MIT Open-source materials outline the basic principles of capacitance, there are a few little but striking dissimilarities between the approaches the two publications take in dissection of the basic physics concept. The open-source material approaches the issue on complex mathematical-physics basis. On the other hand, Advanced Physics for You gives the topic a simplistic outlook. It illustrates with less formulae and more figures. The book is more elaborate and comprehensible in explanation of the same capacitance mechanisms and principles with its concentration on colorful exhibition of concepts. Nonetheless, both publications relay the same information with the same effectiveness to different audiences; MIT open-source material to advanced physicists while Keith and others’ publication present advanced physics concepts to uncomplicated minds since it concentrates on less mathematics, and more on the explanation of the principle behind capacitance. Reference List MIT Open-source. (2014). Capacitance & capacitors. Hawthorn , Massachusetts Institute of Technology. Retrieved from http://ocw.mit.edu/high-school/physics/demonstrations-on-video/conductors-capacitors-dielectrics/ Keith J., Simmone H., Sue H. & John M., (2003). Advanced Physics for You. San Francisco, Fearon Publishers. Read More