REDUCING BATTERY DISCHARGING RATE USING PHOTO-ELECTRIC EFFECT

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Cecil Todd
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1 REDUCING BATTERY DISCHARGING RATE USING PHOTO-ELECTRIC EFFECT Jeet Kumar Gaur, Abhinav Mittal, Bikash Chandra Maurya, B.Tech. 3 rd year students, Mechanical Engineering Department, KIET, Ghaziabad, India jeetkumargaur@gmail.com, Ph Abstract To make the battery work longer once charged the electrons can be made to get over the negative terminal of the battery using the photon energy by the use of a low wave length ultra violet lamp [1]. In process forms a circuit that acts as the charging circuit of the battery. Thus the rate of discharge of the battery reduces and battery life increases. Such an arrangement if used with the battery will tend to recharge the battery when it s being used. Thus the net discharging rate of the battery is reduced. Key words: Electrons, photons, photo-electric effect, Work function, Ultra Violet Lamp. 1. Introduction When charging of the battery occurs using an external electricity source, the electrons that are carried to the positive terminal of the battery are carried back to the negative terminal of the battery by applying an opposite and higher electric field. The photo electric effect is another way of charging the battery using solar energy, but this technology is by using the energy from the sun rays and thus is dependent on the sun. Here is an attempt to combine the usefulness of photo electric effect with the concept of charging to enhance the life of a battery. This can be done using source of photons with energy higher than the threshold frequency of the circuitry material (here it is taken as copper). 2. Related Works In 1905 Albert Einstein in one of his papers about the photoelectric effect, made clear that when any metallic body is illuminated by photons having energy more that the work function of that metal, free electrons get ejected from that body [2]. Work function of any material can be defined as the minimum amount of the energy required to just free the electron from the orbit of the atom of that material. If the energy of the photon is higher than the work function of the material then the extra energy provides kinetic energy to the electrons. Fig 1 Ejection of electrons by photo electric effect Thus came the equation, hv =φ + K.E [3] Where, h=plank s constant=6.63*10^(-34) joule-second v=frequency of the striking photon. hv=total energy of the striking photon φ=work function of the material K.E. =Kinetic energy of the electron The main conclusions of the photoelectric effect are as follows 61

2 1. There is no effect of the photon on the electron it strikes if the value of the work function is higher than the energy of the photon. 2. A photon which is a quantum of energy of light give it s energy to none or one electron 3. No photon can give its energy to more than one electron. Here comes the particulate nature of light. 4. If the value of the work function equals the energy of the photon then the electron gets freed from the orbital but has no kinetic energy to leave. Using this effect solar cell, photo cells or LDRs (Light Detecting Resistors), solar chargeable batteries are made [4]. 3. Reducing the Discharging Rate of Battery Using Photo Electric Effect An arrangement can be attached to the battery via which the external load is connected to the battery. But the effect of reduced discharging rate in battery can be obtained by an arrangement that tends to form a circuitry that tends to charge the battery when in use without using any external source.this arrangement is connected directly to the two terminals of the battery in a vacuum bulb and then via this arrangement the external load is connected. The main compenents used in this arrangement are vacuum bulb, low wavelength UV lamp,semi cylindrical reflecting mirror, copper plates. 3.1 Vacuum bulb This is a glass bulb with vacuum inside.the main purpose of using it is that it prevents the hurdle that would be created for the electrons emited by photo electric effect due to collision with air molecules.this contains the low wavelength UV lamp, copper plates,semi cylindrical reflecting mirror connected as shown below. 3.2 Low wavelength UV lamp This is the source of photons causing the photons electric effect in this arrangement.the lamp is connected to the negative terminal of the battery and placed inside the vacuum bulb.the position of the lamp with respect to the copper plate is such that most photons strike the copper plate. 3.3 Semi cylindrical reflecting mirror This is a miorror which is semi cylindrical in shape.this component of the arrangement is to make use of maximum number of the photon by directing them over the copper plate (a).the position of the mirror is such that most of the photons falling on itget reflected on the copper plate (a). Fig 2 Semi cylindrical reflecting mirror 3.4. Copper plate (a) This copper plate is connected directly to the negative terminal of the battery.this plate is the one from which electrons are ejected as a result of the photo electric effect towards the surface of plate (b). 62

Fig 3 Copper plate (a) 3.5.Copper plate (b) This plate is oriented in space such this electrons reflected from plate (a) as a result of the photo electric effect move to it s surface.

3 Fig 3 Copper plate (a) 3.5.Copper plate (b) This plate is oriented in space such this electrons reflected from plate (a) as a result of the photo electric effect move to it s surface. In Figure 4: (c) is the negative terminal of the battery (g) is the positive terminal of the battery (a),(b) are the two copper plates (f) is the external load Fig 4 Arrangement of complete system In this arrangement the battery terminal (c) that is the negative terminal is connected to a low wavelength ultra violet lamp which is then connected to a copper plate (b).the positive terminal of the battery is connected to the copper plate (a). A semi cylindrical reflecting mirror is placed around the ultra violet lamp to reflect most of the photons on the copper plate (a), the plate (a) is given some curvature in the direction of the lamp. This helps all the electron that get emitted by the photo electric effect due to photons coming from the low wave length UV lamp to move almost towards a point, This point lies on the plate (b).this arrangement containing the UV lamp,semi cylindrical reflecting mirror and the copper plates (a)&(b) are enclosed in a vacuum bulb. And the load is connected to terminals (1) and (2). 63

4 4. Working Now,as the external load is connected the circuit closes and current flows through path (g)(a)(1)(f)(2)(b)(d)(c) but, as the UV lamp blows, it s photons tend to illuminate to the plate (a) due to the arrangement. If the wave length of the UV rays is λ Then, the energy of the photons =hc/λ Let work function of the metal=φ Then, hc/λ=φ + K.E [4] This is the K.E of the ejected electrons. So, The voltage with which these electrons are accelerated, V o = (K.E)/e Where, e=1.6*10 ^ (-19) coulomb This is similar to the motion of electrons, when we charge a battery by external voltage of higher value. So, here also if the voltage with which the electrons are accelerated from copper plate (a) to copper plate (b) is higher than the potential difference between the points of connection of the two plates then this will allow electron to become a part of the current flowing through copper plate (b) in the direction of flow. Thus the current from the output of the battery reduces. Fig 5 Reduction in discharging rate of battery arrangement Here this can be explained taking actual values. The UV lamp of low wave length (10 nano meters) emit photons of energy equal to [hc/(10*10^(-9))]=6.63*10^ (-34) * (3*10^8)/(10^(-8)) =1.989*10^ (-17) joule Which is more then the work function of copper (4.7ev or 7.52*10^ (-19) joule) [5]. So by the photo electric equation K.E. = hv-φ =1.9138*10^ (-17) joule With this kinetic energy the electrons emitted from plate (a) have energy= ev that is as if it s accelerated by volt.so even a battery of 110 volts will get charged this way. But, since not all photons can be participating in the photoelectrical electron emission thus there is discharging of the battery but at a very low rate. Take the potential at point (b) be 12 volts then the charging voltage required is low (18 to 20 volts) so the wave length of UV lamp can be increased accordingly to get desired result. Thus the electron reach the plate (b) and now tends to flow along path (b)(2)(f)(1)(a)(g).whenever the circuit is completed (that is load is connected )this effect occurs. The discharging rate of the battery thus reduces as the rate of electrons reaching the positive terminal of battery from the negative terminal reduces and from a circuit (b)(2)(f)(1)(a)(b). The life of the battery increases thus once charged the battery will work longer due to reduced discharging rate. 64

5 5. Conclusions As the current from the battery remains low as compared to the former case of usual batteries the discharging of battery occurs at a lower rate with time. If the number of photons being directed over the copper plate (a) is made more by efficient use of the reflecting surface of the semi cylindrical mirror then the life of battery can be increased remarkably. This can in turn, if used over a large scale save energy widely, also if the battery life is extendable for much time then this can be used in long journey space vehicles as the energy source also if used in household widely it will reduce the overall consumption of electricity. Although it s not a new energy resource but it acts as a method to reduce the present rate of resource consumption at the same time maintaining the rate of energy consumption. Acknowledgement The Authors would like to thank Mr. Sachin Rathor and Mr. Satish Patel for his support and guidelines in completing the paper. References [1] [2] Pranawa C. Deshmukh and Shyamala Venkataraman, 100 Years of Einstein s Photoelectric Effect, Department of Physics Indian Institute of Technology Madras Chennai [3] [4] [5] 65

WAVES AND PARTICLES. (c)

WAVES AND PARTICLES. (c) WAVES AND PARTICLES 1. An electron and a proton are accelerated through the same potential difference. The ration of their De Broglie wave length will be -- (a) (b) (c) (d) 1 2. What potential must be