Energy Transfer in Electrical Circuits - Research Paper Example

Energy Transfer in Electrical circuits Energy Transfer in Electrical circuits In most of the energy generation systems, energy is converted from one form to another form. In power generation units, the chemical energy trapped in the coal is converted to thermal energy at first stage and then converted to electrical energy. In the similar manner, battery holds the energy that is generated through chemical reactions. Wind generators convert the aerodynamic energy of wind and convert it to electrical energy. Solar panels convert solar light energy into electrical energy, etc. In electrical circuits, energy is transferred so that it can be made useful according to the requirements. Home appliances and industries transform energy into other forms to a desired form. Electric circuits are utilized for these operations. Energy storage and sources Energy is not in the form of matter that can be saved. “Energy can neither be created nor it can be destroyed, it can be changed from one form to another form” (Moan & Smith, 2007). The phrase “source of energy” or “sources of energy” is a wrong phrase as energy is impossible to create. We can only alter it from one form to another form. Battery converts chemical energy to electrical energy. Battery does not generate energy. A power plant converts chemical energy of fuel to electrical energy. Fossil fuels had converted solar energy to chemical energy (Moan & Smith, 2007). Ideal energy conversion system and actual energy conversion system An ideal energy conversion system is that that has no losses. One form or energy is converted to the other desired form without any losses. The efficacy of such a system is 100%. It means that the ratio of inputs and outputs equal 1. If usable outputs = inputs, then we have 100% efficiency. Practically it is impossible to have an ideal system. A practical energy conversion system does have some losses and thus the desired output is always less than the input. In power generation, internal combustion engine are only 40% efficient. 60% of the input energy is wasted as heat energy that is undesired. If a combined cyclic plant is utilized to convert energy, 80% efficiency can be achieved, as a carefully designed heat recovery system recovers most of the thermal energy that goes to waste. In the similar manner, an electric motor does not convert all the input energy to mechanical energy, some of the energy is dissipated as heat and bearing losses. An electric bulb wastes about 95% of energy, which is dissipated in the form of heat and converts only 5% of the energy to light energy (Bbc.co.uk, 2014). Energy and power There is much difference in energy and power. Energy yields power. Electrical energy is the product of electrical power and time. If electrical energy is denoted by “e” power is denoted by P and time period is define by t, then e = P x t… (1) According to Ohm’s law, V= I x R… (2), where V is the Voltage of the electoral circuit, I is the current dissipated in the circuit and R is the resistance of the circuit. Power is the product of voltage taken by the electrical and electronic devices in the circuit and current dissipated by the circuit. P = V x I … (3), Combining 1, 2 and 3 we attain, e = I2 x R x t, where P = I2 x R, In this way we can say that, all the terms in an electrical circuit are correlated to each other. Electrical potential and Battery Electrical circuit requires a path for the flow of electrons. Energy is transferred with the help of free electrons on conductors. Conductors like metals have free electrons that allow them to conduct electrical current. Electrons move from positive to negative terminal. If in any case, the path remains incomplete, electrons will not floe and thus no energy will be passed through the circuit. Electric potential is the capacity of the path to flow electrons. Electrical potential is the potential difference between the two terminals of the battery of the sources. If one terminal has the potential of 12 volts and one has zero volts, the potential difference will be 12 V (Bbc.co.uk, 2014). Energy transfer in an electrical circuit with a Load Consider a simple electrical circuit with a bulb (Load/ Resistance) and a battery (Source). The flow of electrons, as shown in the image is from the negative terminal to the positive terminal. In the other image, the complete circuit is shown, where battery is the source of energy, bulb is the load that converts energy into another form and switch controls the flow of completes or breaks the path of current. Consider if bulb has some resistance and takes some current, then we can evaluate the current dissipated by the bulb through ohms law or (2). The energy taken by the bulb can be calculated by e = I2 x R x t, where t is the time period in which the bulb remains ON (Patrick & Fardo, 1999). Energy transfer in Parallel loads Consider a circuit with three parallel loads or consider a circuit with parallel resistors. In the image below, V denotes the battery voltages. In this circuit there are three different paths for the flow of current. The current is distributed in each of the path. Each load resistor takes its share of current and from the source or battery. The voltage remains the same in this circuit. If the parallel circuit is applied to the battery and bulbs example, all the bulb glow to their maximum potential converting maximum amount of energy as much these can. In this circuit current to each load resistance can be calculated with the help of equation (2) that evaluates: In the similar manner, power can be calculated through: P1 = I12 x R1, P2 = I22 x R2, P1 = I12 x R2 And energy converted by each resistor can be evaluated through: e1 = I12 x R1 x t1, e2 = I22 x R2 x t2, e1 = I12 x R2 x t3 Where, t1, t2, t3 are the ON time periods for each of the loads or load resistors (Patrick & Fardo, 1999). Energy transfer in series loads Now consider a circuit with three resistances in series. Here V denotes the battery voltages. In the circuit shown above, there is only one path for the flow of electrons. Current flows form only a single path. In this circuit, the current remains the same through out the circuit. However, voltage drops at each resistive load. The amount of power is thus limited. The amount of energy taken by each load is different due to the difference between the load resistances. For this type of circuit the energy taken by the circuit will be. e1 = I2 x R1 x t, e2 = I2 x R2 x t, e1 = I2 x R2 x t, Here, the current and ON time period remains same for each individual load. How electrons flow from a battery The positive terminal of the battery is deficient of electrons and negative terminal of the battery have plenty of electrons. The positive terminal drifts the electrons from the negative terminal. If we apply a bulb in between the path, the bulb glows due to the resistance of the filament. The electric field generated by the battery is due to the positive and negative charge separation by the battery. Electric field is the term that is used to identify the flow the electrons due to potential difference. Electromagnetic fields and energy transfer Electrical and magnetic fields temporarily or permanently store energy. In the similar manner, both the fields are responsible for the transmissions of energy. If “E” is the electric field, then the energy density can be defined as: Here is the constant according to coulombs law. Energy density of the system depends of the electric field, the stronger the electric field; the larger will be the energy density (Andrews & Bittner, 1993). If B is the magnetic field, then the energy density of the magnetic field can be given as: Here, is the constant. Energy Transfer in a piece of wire Consider a piece of wire with total length d and radius “r”, Cross sectional area “A” (A = 2πrd), current “I” passes through the wire. ‘S’ is the poynting vector, B is the magnetic field and E is the electric field (Galili & Goihbarg, 2005). As we can clearly see in the figure that both the electric and magnetic fields are perpendicular to the pointing vector, the cross product of the Electric and magnetic field yields; E x B = EB, As, The input power to the piece of wire is “P” and it is defined as the product of pointing vector and curved area of the wire (Andrews & Bittner, 1993). P = SA, here A = 2πrd, and As we know that potential difference is the product of electric field and length of wire, we can write: Or Magnetic field is the ratio of product of current passing through the conductor and permeability of the magnetic field and the perimeter of the conductor Substituting, (6) and (7) in (5) we will attain, References Andrews, D., & Bittner, A. (1993). Energy transfer in a static electric field. Journal Of Luminescence, 55(5-6), 231-242. doi:10.1016/0022-2313(93)90018-i Bbc.co.uk,. (2014). BBC - KS3 Bitesize Science - Energy transfer and storage : Revision, Page 3. Retrieved 12 November 2014, from http://www.bbc.co.uk/bitesize/ks3/science/energy_electricity_forces/energy_transfer_storage/revision/3/ Galili, I., & Goihbarg, E. (2005). Energy transfer in electrical circuits: A qualitative account. American Journal of Physics, 73(2), 141. doi:10.1119/1.1819932 Moan, J., & Smith, Z. (2007). Energy use worldwide. Santa Barbara, CA: ABC-CLIO. Patrick, D., & Fardo, S. (1999). Understanding DC Circuits. Oxford: Elsevier Science. Read More