47135_HW8-1

# 47135_HW8-1 - ragsdale(zdr82 – HW8 – ditmire –(58335...

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

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

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

Unformatted text preview: ragsdale (zdr82) – HW8 – ditmire – (58335) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A conductor consists of an infinite number of adjacent wires, each infinitely long and carrying a current I (whose direction is out-of- the-page), thus forming a conducting plane. A C If there are n wires per unit length, what is the magnitude of vector B ? 1. B = μ I 2 2. B = 4 μ I 3. B = 2 μ nI 4. B = 4 μ nI 5. B = μ I 6. B = 2 μ I 7. B = μ nI 4 8. B = μ I 4 9. B = μ nI 2 correct 10. B = μ nI Explanation: l W A C B B By symmetry the magnetic fields are equal and opposite through point A and C and hori- zontally oriented. Following the dashed curve in a counter-clockwise direction, we calculate contintegraldisplay vector B · dvectors , which by Ampere’s law is propor- tional to the current through the dashed loop coming out of the plane of the paper. In this problem this is a positive current. Hence vector B along the horizontal legs points in the di- rection in which we follow the dashed curve. Ampere’s Law is contintegraldisplay vector B · dvectors = μ I . To evaluate this line integral, we use the rect- angular path shown in the figure. The rectan- gle has dimensions l and w . The net current through the loop is nI l . Note that since there is no component of vector B in the direction of w , we are only interested in the contributions along sides l contintegraldisplay vector B · dvectors = 2 B l = μ nl I B = μ nI 2 . 002 10.0 points A superconducting solenoid has 5810 turns / m and carries a current of 2000 A. What is the magnetic field generated inside the solenoid? The permeability of free space is 1 . 25664 × 10 − 6 T · m / A. Correct answer: 14 . 6021 T. Explanation: Let : n = 5810 turns / m , μ = 1 . 25664 × 10 − 6 T · m / A , and I = 2000 A . ragsdale (zdr82) – HW8 – ditmire – (58335) 2 The magnetic field generated inside the solenoid is B = μ nI = ( 1 . 25664 × 10 − 6 T · m / A ) × (5810 turns / m) (2000 A) = 14 . 6021 T . keywords: 003 (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. Q RC e − t/Q 2. RC Q e t/ ( RC ) 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 ) = Qe − 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 ) ....
View Full Document

{[ snackBarMessage ]}

### Page1 / 11

47135_HW8-1 - ragsdale(zdr82 – HW8 – ditmire –(58335...

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

View Full Document
Ask a homework question - tutors are online