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There is an electric potential of 120 V at a point that is 0.25 m away from a charge. Find the magnitude and sign of the charge.

There is an electric potential of 120 V at a point that is 0.25 m away from a charge. Find the magnitude and sign of the charge.

College Physics
College Physics
11th Edition
ISBN:9781305952300
Author:Raymond A. Serway, Chris Vuille
Publisher:Raymond A. Serway, Chris Vuille
Chapter1: Units, Trigonometry. And Vectors
Section: Chapter Questions
Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...
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Exercise There is an electric potential of 120 V at a point that is 0.25 m away from a charge. Find the magnitude and sign of the charge. Potential at a Point Due to Several Charges Let us say we have a group of charges arranged as shown in Figure 2.5. Q, Q2 Q3 Figure 2.5. Potential at a point due to several charges The potential at point P due to charges Q1, Q2, and Q3 cab be calculated by getting the potential due to each of the three charges, V,, V2, and V3. Then, we get the sum of the three potentials. In equation form, we get: V, = Ev. = kE or, Q3 +k- r3 Vp = k + k r2 Exercise Four-point charges are placed at the four corners of a square that is 30 cm on each side. Find the potential at the center of the square given that each of the four charges has a magnitude of +2 μC. Electric Potential Energy at a Point due to a Charge If we have a charge +q at infinity (which is at zero potential) and it is brought to a point P, r distance away from a charge Q, we can find the potential difference AV, to be equal to a potential at P minus the potential at infinity (0). In equation form, Qq APE = k - The work required to bring q from infinity to P is also the PE of the system. Exercise Two-point charge of 0.04 µC and 0.16 µC are 20 cm apart in air. (a) What is the potential energy of the system? (b) Find the work required to bring two charges to 10 cm from each other. Electric Potential Energy of Several Charges 0. Suppose we have a system of charges Q1, Q2, and Q3 (see Figure 2.6). In the diagram, we have three pairs of charges: Q,Q2, Q2Q3, and Q1Q3. The total potential energy of the system is: Q.Q2 EPEtotal = k Q2Q3 + k- Q123 + k r23 r13 Figure 2.6. A system of charges
Transcribed Image Text:Exercise There is an electric potential of 120 V at a point that is 0.25 m away from a charge. Find the magnitude and sign of the charge. Potential at a Point Due to Several Charges Let us say we have a group of charges arranged as shown in Figure 2.5. Q, Q2 Q3 Figure 2.5. Potential at a point due to several charges The potential at point P due to charges Q1, Q2, and Q3 cab be calculated by getting the potential due to each of the three charges, V,, V2, and V3. Then, we get the sum of the three potentials. In equation form, we get: V, = Ev. = kE or, Q3 +k- r3 Vp = k + k r2 Exercise Four-point charges are placed at the four corners of a square that is 30 cm on each side. Find the potential at the center of the square given that each of the four charges has a magnitude of +2 μC. Electric Potential Energy at a Point due to a Charge If we have a charge +q at infinity (which is at zero potential) and it is brought to a point P, r distance away from a charge Q, we can find the potential difference AV, to be equal to a potential at P minus the potential at infinity (0). In equation form, Qq APE = k - The work required to bring q from infinity to P is also the PE of the system. Exercise Two-point charge of 0.04 µC and 0.16 µC are 20 cm apart in air. (a) What is the potential energy of the system? (b) Find the work required to bring two charges to 10 cm from each other. Electric Potential Energy of Several Charges 0. Suppose we have a system of charges Q1, Q2, and Q3 (see Figure 2.6). In the diagram, we have three pairs of charges: Q,Q2, Q2Q3, and Q1Q3. The total potential energy of the system is: Q.Q2 EPEtotal = k Q2Q3 + k- Q123 + k r23 r13 Figure 2.6. A system of charges
Exercise Three-point charges 10 C, -20 C, and -50 C are at the three consecutive corners of a square 10 cm on a side. What is the total potential energy of the system? The Electron Volt Let us say we have an electron in an electric field between two parallel plates which are oppositely charged. If the electric field between the two plates is directed upward, which means that the lower plate is positive and the upper plate is negative, the force it exerts on the negative electron is directed downward. To move it from the lower plate to the upper plate, work must be done on it. An external force directed upward must be exerted to be able to move it from the lower plate to the upper plate. This suggests that the potential energy of the electron at the upper plate is greater than its potential energy at the lower plate. If the electron is placed at the upper plate, it will accelerate downward thereby decreasing its potential energy. This decrease in potential energy means an increase in kinetic energy. ΔΚΕ qV The charge of an electron is 1.6 x 10-19 C. Therefore, when it moves through a potential difference of 1 volt, its kinetic energy increases by AKE = 1.6 x 10-19 C (1 V) = 1.6 x 10-19 This is the amount of energy equivalent to one electron volt. In other words, one electron volt is equivalent to 1.6 x 10-19 J of kinetic energy. An electron volt is a unit of energy given as eV. It is, therefore, convenient to use this unit of energy in dealing with atomic particles. Exercise Let us say that a proton has a kinetic energy of 4.8 x 10-19J. What is the energy in electron volts?
Transcribed Image Text:Exercise Three-point charges 10 C, -20 C, and -50 C are at the three consecutive corners of a square 10 cm on a side. What is the total potential energy of the system? The Electron Volt Let us say we have an electron in an electric field between two parallel plates which are oppositely charged. If the electric field between the two plates is directed upward, which means that the lower plate is positive and the upper plate is negative, the force it exerts on the negative electron is directed downward. To move it from the lower plate to the upper plate, work must be done on it. An external force directed upward must be exerted to be able to move it from the lower plate to the upper plate. This suggests that the potential energy of the electron at the upper plate is greater than its potential energy at the lower plate. If the electron is placed at the upper plate, it will accelerate downward thereby decreasing its potential energy. This decrease in potential energy means an increase in kinetic energy. ΔΚΕ qV The charge of an electron is 1.6 x 10-19 C. Therefore, when it moves through a potential difference of 1 volt, its kinetic energy increases by AKE = 1.6 x 10-19 C (1 V) = 1.6 x 10-19 This is the amount of energy equivalent to one electron volt. In other words, one electron volt is equivalent to 1.6 x 10-19 J of kinetic energy. An electron volt is a unit of energy given as eV. It is, therefore, convenient to use this unit of energy in dealing with atomic particles. Exercise Let us say that a proton has a kinetic energy of 4.8 x 10-19J. What is the energy in electron volts?
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