University:
Kentucky State University
Course:
PHY 212 | General Physics II
Academic year:

2019
Views:

382

Pages:

13
Author:

Ciullismr

**CH 26: Current and Resistance** i = dq/dt = [I] / [T] = C/s = Ampere = A ∫dq = ∫idt **Current Density:** J = the amount of current per unit area J = Δi / A [J] = [I] / [A] = A/m² ⇒ J = Δi / ΔA → di/dA ∫di = ∫J.dA ⇒ i = ∫J.dA **Ex 26-2 page 687** The total current: **a) J = Constant = C (uniform)** i = ∫J.dA = ∫JdA cosθ θ = 0 i = J∫dA = JA i = CA = C(πR² - π(R/2)²) = 3/4 πR²C **b) J(r) = ar² (non-uniform)** i = ∫J.dA = ∫JdA cosθ = ∫(ar²) (2πrdr) = 2πa ∫r³dr = 2πa [r⁴/4]R₀R₁ = πa/2 [R₁⁴ - (R₀)⁴] **Power in Electric Circuits** ΔU = ΔqV i = Δq/Δt P = ΔU/Δt = iV = iε = iV = i(IR) Produced power (Generated power) P = i²R = V²/R Dissipated power ⇒ Pbattery = iV = iε ⇒ Pdissipated = i²R = V²/R In R: P = i²R = V²/R **P39 Page 702** V = 120V, R = 14Ω **Q: What is the electrical energy transferred to thermal energy?** P = ΔU/Δt = V²/R = (120)² / 14 = C Watts **H.W** **P41 Page 702** **P41 Page 702** R = ? V = 12 V P = 54 W V₂ = 11.8 V P₂ = ? Sol: R₁ = R₂ P₁ = V₁²/R₁ ⇒ R₁ = V₁²/P₁ R = (12)²/54 = 2.67 Ω P₂ = V₂²/R = (11.8)²/2.67 = 52 W **H.W P27 Page 701**