Potential Difference

Potential A charged particle has potential energy due to its position relative to another charged object (Electric Potential Energy) The + particle has potential energy at position A Once the particle moves to B all PE is changed to KE (-) plate has low potential, (+) plate has high potential

Definition Potential (V) is defined as the PE per charge V = PE/ q Units J/C 1 J/C = 1 Volt (V) Note that only changes in PE are measurable – called Potential Difference Potential difference = Voltage

Equation ΔPE = qV Voltage is a measure of how much energy an electric charge can acquire Since change in energy is the ability to do work, it is also a measure of how much work W = qV

Measurement Voltmeter – instrument used to measure V between 2 points

Example 1 An electron in the picture tube of a TV is accelerated from rest through a potential difference of +5000V a) what is the change in PE b) what is the electron’s speed c) how much work is done?

Example 2 The terminals of a 12V battery differ in potential by 12V. Suppose that a wire is connected between the + and – terminal and 3.0 C of charge travels between them. How much work is done?

Example 3 An electron loses 3.45 x J of PE as it moves from plate A to B in a computer monitor. What is the voltage between the plates and which plate has the highest potential?

Units of Electric Field Either N/C or V/m

Example Two parallel plates are charged to 50V. If the plates are separated by.050m, what is the electric field they produce?

Small Energy Unit J is traditional unit of energy, but with very small particles this unit appears very large electron voltSmaller unit of energy is used for these called the electron volt (eV) Before doing a problem, always change eV to J 1 eV = 1.6 x J

Example What potential difference is needed to give a particle of charge of 3μC a total of 3.54 x 10 9 eV of energy?