Ch 23 Electric Potential_2009

Ch 23 Electric Potential_2009 - Electric Potential Ch 23 In...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Electric Potential Ch 23 In mechanics, the idea of work and energy made a number of difficult problems much easier to solve. For example the work it takes to push a box across a titled floor with friction. In this chapter we combine the development of work and energy of mechanics with electrical force, charge and electric fields .
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Electric Potential Energy Recall for mechanical systems work done by a force F between points a and b was defined to be: = = b a b a dr F r d F W cos φ dr is an infinitesimal displacement along the particle’s path and φ is the angle between F and dr.
Background image of page 2
If the force is conservative, ( does not depend on time; only on displacement ), then the work done by F can be expressed in terms of potential energy U . Friction is a non-conservative force; gravity is a conservative force. U E K W - = = . . Work energy theorem extended into the negative of the change of the potential energy: f f i i K U W K U + = + + Conservation of Energy principle with work. F k z U j y U i x U U = + + = - ˆ ˆ ˆ
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Electric Potential Energy in a Uniform Field Let us consider the work done on a test charge q 0 (always positive and small). As the charge is moved from point a to point b , the force acting on the charge is constant (because the electric field was shown to be between two charged plates) and F e = q 0 E Ed q Fd W 0 = = The work done on the charge by the constant force F over distance d is:
Background image of page 4
Ed q Fd W 0 = = This is the electrical work. In form is exactly like the work gravity would do on a particle falling a distance d . Likewise to gravity, which has a potential of mgy , the electrical potential above is U e = q 0 Ey When a test charge moves from y 1 to y 2 , the work done on the charge particle by the electric field is: ( 29 ( 29 ) ( 2 1 0 1 0 2 0 1 2 y y E q Ey q Ey q U U U W - = - - = - - = - =
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
( 29 ) ( 2 1 0 1 2 y y E q U U U W - = - - = - =
Background image of page 6
Electric potential For an infinitesimal displacement ds of a charge, the work done by the electric field is F e ·d s = q 0 E ·d s. As this amount of work is done by the electric field, the potential energy of the charge-field system is changed by an amount dU = - q0 E ·d s. The change in potential to move a charge in an electrical field from A to B is then given by: - = B A s d E q U 0
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
- = B A s d E q U 0 Because the Electric field is conservative, it does not matter what path connects A and B , the change in potential will be the same. The potential energy per unit charge is U/q 0 . This value is independent of q 0 and has a value at every point in an electric field. U/q 0 is called the electric potential, or simply the potential. The electric potential (a number or scalar not a vector) at any point in the electric field is defined by: 0 q U V =
Background image of page 8
The potential difference between in two points A and B in an electric field more generally is given by: - = = B A ds E q U V 0 Hence W = qV The unit of a volt is Joules/Coulomb = J/C .
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/05/2011 for the course PHYS 4B taught by Professor W.christensen during the Summer '09 term at Irvine Valley College.

Page1 / 75

Ch 23 Electric Potential_2009 - Electric Potential Ch 23 In...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online