Fe e fh dr bb whistheworkdonebythehandontheball

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: a way that PE decreases 34 ACT You hold a positively charged ball and walk due west in a region that contains an electric field directed due east. FE E FH dr BB WH is the work done by the hand on the ball WE is the work done by the electric field on the ball Which of the following statements is true: 14 A) WH > 0 and WE > 0 B) WH > 0 and WE < 0 C) WH < 0 and WE < 0 D) W < 0 and W > 0 Not a conservative force. Does not have any ∆ U. Conservative force: ∆ U = - WE FE FH E dr B) WH > 0 and WE < 0 Is ∆ U positive or negative? positive or negative? A) Positive BB 16 B) Negative Two ways to tell: Two 1 ) ∆ U opposite in sign to W done by E field 2) If released, ball will want to move toward lower potential energy, or in direction of force (to the left) force Example: Two Point Charges Calculate the change in potential energy for two point charges originally very far apart moved to a separation of “d”. Work done by q1 on q2 is NEGATIVE, so ∆ U is POSITIVE. Compute magnitude o f wo rk to g e t ∆ U. d d q1q2 q1q2 W = ∫ k 2 dr = k r12 d ∞ q1 q1q2 ∆U = k d q2 1 q1q2 ≡ 4πε 0 d C h a rg e d p a rtic le s w/ s a m e s ig n h a ve a n inc re a s e in p o te ntia l e ne rg y wh e n b ro ug h t c lo s e r to g e th e r. Fo r p o int c h a rg e s o fte n c h o o s e r=infinity a s “ze ro ” p o te ntia l e ne rg y . 19 ACT ACT Case A Case B BB d 2d In case A two negative charges which are equal in magnitude are separated by a distance d. In case B the same charges are separated by a distance 2d. Which configuration has the highest potential energy? A) Case A B) Case B 22 ACT Discussion ACT Discussion • As usu...
View Full Document

This document was uploaded on 02/13/2014.

Ask a homework question - tutors are online