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PHY 2049: Physics II. We begin with a live clicker today. Wileyplus homework should be fully operational. Tea and Cookies: We meet on Tuesdays at 4:00PM for tea and cookies in room 2165. quiz.
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PHY 2049: Physics II • We begin with a live clicker today. • Wileyplus homework should be fully operational. • Tea and Cookies: We meet on Tuesdays at 4:00PM for tea and cookies in room 2165.
quiz • The electric field at a distance of 1 m from an isolated point particle with a charge of 2×10−9 C is: • A. 1.8N/C B. 180N/C C. 18N/C D. 1800N/C E. none of these
Quiz 2 • An isolated charged point particle produces an electric field with magnitude E at a point 2m away from the charge. A point at which the field magnitude is 4E is: • A. 1m away from the particle • B. 0.5m away from the particle • C. 2m away from the particle • D. 4m away from the particle • E. 8m away from the particle
PHY 2049: Physics II Last week • Coulomb’s law, Electric Field and Gauss’ theorem Today • Electric Potential Energy and Electric Potentials • Numerous cases
Potential Energy and Potential • Force => work => change in K=> change in Potential energy • ΔU = Uf – Ui = -W = - ΔK • Work done is path independent. K+U = constant. U = k q1 q2/r : interaction energy of two charges. Sign matters
PHY 2049: Physics II • Electric Potential • V = U/q = -W/q • Units of Joules/coulomb = volt • 1 eV = e x 1V = 1.6 x 10-19 J • Also • V = kq/r • Vf –Vi = -∫E.ds • In case of multiple charges, add as a number
Neg., lower • ? • Pos., higher • Neg., higher • Pos., higher PHY 2049: Physics II 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 • Vf-Vi = -∫ k q/r2 dr • Choose Vi = V (∞)=0 • V(r) = kq/r
V = kpcosθ/r2 • E = -∂V/∂s = - • Uniformly charged disk • V = ??
A C B (24 - 6)
A O dq (24 - 8)
. P r dq (24 - 7)
V B A S q S V (24 - 11)
A B V+dV V (24 - 13)
A B V+dV V (24 - 14)
q2 y r12 r23 q1 r13 q3 x O (24 - 15)
y Step 1 q1 x O Step 2 q2 y r12 q1 x O Step 3 q2 r12 y q1 r23 r13 q3 O x (24 - 16)
conductor path B A (24 - 17)
R (24 - 20)