Homework_11-solutions

Homework_11-solutions - toupal(rgt374 – Homework 11 –...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

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

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

Unformatted text preview: toupal (rgt374) – Homework 11 – Chiu – (58295) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points A capacitor of capacitance C has a charge Q at t = 0. At that time, a resistor of resistance R is connected to the plates of the charged capacitor. Find the magnitude of the dis- placement current between the plates of the capacitor as a function of time. 1. RC Q e − t/ ( RC ) 2. Q RC e − t/Q 3. Q RC e − t/ ( RC ) correct 4. Q RC e t/ ( RC ) 5. RC Q e t/ ( RC ) Explanation: Basic Concept RC circuits. Displacement Current. The displacement current is defined to be I d = ǫ d Φ E dt . The electric field inside a capacitor is essen- tially uniform and E = q ǫ A . Since the charge on a capacitor in a discharging RC circuit is given by q ( t ) = Q e − t/RC , the displacement current is found by I d = ǫ d Φ E dt = ǫ d dt parenleftbigg q ǫ A A parenrightbigg = dq dt = − Q RC e − t/ ( RC ) . Note that the displacement current equals the actual current in the wires to the capacitor. Thus, the Ampere-Maxwell law tells us that vector B will be the same regardless of which current we evaluate. 002 (part 2 of 2) 10.0 points Given C = 4 μ F, Q = 29 μ C, R = 252 kΩ, and ǫ = 8 . 85419 × 10 − 12 C 2 / N · m 2 , at what rate is the electric flux between the plates changing at time t = 0 . 2 s? Correct answer: − 2 . 66452 × 10 6 Vm / s. Explanation: Let : ǫ = 8 . 85419 × 10 − 12 C 2 / N · m 2 , t = 0 . 2 s , C = 4 μ F , Q = 29 μ C = 2 . 9 × 10 − 5 C , and R = 252 kΩ = 2 . 52 × 10 5 Ω . From the discussion in the previous part, we know that d Φ E dt = I d ǫ = − Q ǫ RC e − t/ ( RC ) = − 2 . 9 × 10 − 5 C ǫ (2 . 52 × 10 5 Ω) (4 × 10 − 6 F) × e bracketleftbigg − . 2 s (2 . 52 × 10 5 Ω)(4 × 10 − 6 F) bracketrightbigg = − 2 . 66452 × 10 6 Vm / s . 003 10.0 points What is the fundamental source of electro- magnetic radiation? 1. None of these 2. current 3. any charge 4. voltage 5. an accelerating charge correct Explanation: The fundamental source of electromagnetic radiation is oscillating electric charges, which emit oscillating electric and magnetic fields. toupal (rgt374) – Homework 11 – Chiu – (58295) 2 004 10.0 points According to Maxwell’s equation, the speed of light in a vacuum is 1. greater for radio waves than for visible light. 2. a function of the distance from the source. 3. independent of frequency. correct 4. greater for visible light than for radio waves. 5. a function of the size of the source. Explanation: Application of Faraday’s Law and the Ampere-Maxwell equation to EM radiation results in the prediction that the speed of light is c = 1 √ μ ǫ , independent of frequency....
View Full Document

This note was uploaded on 04/26/2009 for the course PHY 58310 taught by Professor Chiu during the Spring '09 term at University of Texas.

Page1 / 11

Homework_11-solutions - toupal(rgt374 – Homework 11 –...

This preview shows document pages 1 - 3. Sign up to view the full document.

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