PHY 2049 Physics II n n Hopefully all

PHY 2049: Physics II n n Hopefully all homework problems have been solved. Please see me immediately after the class if there is still an issue. Tea and Cookies: We meet on Wednesdays at 4: 00 PM for tea and cookies in room 2165.

quiz n n The electric field at a distance of 10 cm from an isolated point particle with a charge of 2× 10− 9 C is: A. 1. 8 N/C B. 180 N/CC. 18 N/C D. 1800 N/C E. none of these

Quiz 2 n n n An isolated charged point particle produces an electric field with magnitude E at a point 2 m away from the charge. A point at which the field magnitude is E/4 is: A. 1 m away from the particle B. 0. 5 m away from the particle C. 2 m away from the particle D. 4 m away from the particle E. 8 m away from the particle

PHY 2049: Physics II Last week n Coulomb’s law, Electric Field and Gauss’ theorem Today n Electric Potential Energy and Electric Potentials n Numerous cases

Potential Energy and Potential n n n U = k q 1 q 2/r : interaction energy of two charges. Sign matters Force => work => change in K=> change in Potential energy ΔU = Uf – Ui = -W = - ΔK Work done is path independent. K+U = constant.

PHY 2049: Physics II n Electric Potential n n V = U/q = -W/q Units of Joules/coulomb = volt 1 e. V = e x 1 V = 1. 6 x 10 -19 J Also n n n V = kq/r Vf –Vi = -∫E. ds In case of multiple charges, add as a number

PHY 2049: Physics II 1. 2. 3. 4. 5. Neg. , lower ? Pos. , higher Neg. , higher Pos. , higher Can you tell the sign of the charge by looking at its behavior over a surface of potentials. Is the speed at the end bigger or smaller than in the beginning.

PHY 2049: Physics II n n n Vf-Vi = -∫ k q/r 2 dr Choose Vi = V (∞)=0 V(r) = kq/r

n n n V = kpcosθ/r 2 E = -∂V/∂s = Uniformly charged disk n V = ? ?

A C B (24 - 6)

O dq A (24 - 8)

PHY 2049: Physics II

. P r dq (24 - 7)

(24 - 9)

(24 10)

V A B q S S V (24 11)

(24 -

(24 13) A B V V+d. V

(24 14) A B V V+d. V

(24 15) q 2 y r 12 r 23 q 1 r 13 O q 3 x

y Step 1 q 1 x O Step 2 y q 1 r 12 q 2 x O y Step 3 r 12 q 1 r 23 r 13 q 3 O x (24 16)

(24 17) conductor path B A

(24 18)

(24 19)

(24 20) R