PHYS 102 Study Guide - Midterm Guide: Magnetic Flux, Electric Flux, Dipole Antenna

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rubymarten89

10 Sep 2016

School

University of Illinois

Department

Physics

Course

PHYS 102

Professor

Kuehn David

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Document Summary

A conducting bar moves in a uniform b field at speed v: magnetic force pushes electrons to top, leaves + charge at bottom of bar, separated and + charge induces e field and v. = e ind l = v b ext l. Motional emf: at equilibrium, forces must sum to zero, f b = v b ext = f e = e ind. + charges in moving bar experience force down. (recall e- actually move, opposite to current: the conducting bar moves to the right in the opposite b field (b field into page) Both bars generate equal current i down and opposite emfs net current = zero. Where does the energy come from to generate electricity: moving bar carries current, so b field exerts force f bar. F bar is not the same as f b, which drives current around loop. F bar opposes v, so bar decelerates.

Related Questions

The bar in Figure OQ31.6 moves on rails to the right with a velocity , and a uniform, constant magnetic field is directed out of the page. Which of the following statements are correct? More than one statement may be correct.

(a) The induced current in the loop is zero.

(b) The induced current in the loop is clockwise.

(d) An external force is required to keep the bar moving at a constant speed.

(e) No force is required to keep the bar moving at a constant speed.

bluebear600

A metal bar of length L is attached to two vertical metalrailsas sketched in the figure below. The connections arefrictionless,but allow current to flow between the rails and thebar. There is aconstant horizontal magnetic field directedperpendicular to thearea enclosed by the bar and rails.

(a) What closed path should we use for applying Faraday'slawto find the current induced in the bar? 1 Any closed loopwillwork. The perimeter surrounding the area enclosed by the barandthe rails should be the path chosen to use with Farday'slaw.

(b) Suppose the bar is at a height z above the bottom. Findthemagnitude and direction of the magnetic flux Î¦B. (Use thefollowingvariables as necessary: B, L, and z.) magnitude Î¦B =2 direction 3---Select--- out of the page into the page

(c) If the bar is moving downward at a speed v, is the fluxinpart (b) increasing or decreasing with time? 4increasingdecreasing

(d) What is the induced emf across the bar? (Use thefollowingvariables as necessary: B, L, and v.) || = 5 (e) Use youranswer topart

(d) to get the current I in the circuit. Be sure to givethedirection of I. (Use the following variables as necessary: B, L,R,and v.) magnitude I = 6 direction 7 ---Select---clockwisecounterclockwise

(f) Now find the magnetic force on the bar. Notice thatthemagnitude of this force increases as v increases. (Usethefollowing variables as necessary: B, L, R, and v.) F = 8

(g) What is the direction of the force on the bar? 9upwardsdownwards

(h) If the bar has a mass m, there will also be agravitationalforce on the bar. Eventually, the bar will reach aspeed v at whichthe gravitational and magnetic forces cancel sothat the total forceon the bar is zero. Find v. (Use the followingvariables asnecessary: B, g, L, m, and R.) v = 10

Please show work, I know this is a long question willratelife-saver !

1a) Faraday discovered that a current is induced in a coil

A) only when the N pole of a magnet is inside the coil
B) only when the S pole of a magnet is inside the coil
C) only when there is a magnetic field inside the coil
D) only when the magnetic field inside the coil is changing

1b). A conductor moves through a uniform magnetic field at speed v and has a motional emf V created across it. If the conductor were to move twice as fast through the magnetic field, the motional emf would be:

A) V
B) 2V
C) 4V
D) V/2
E) V/4

1c) In the conducting rail discussed in section 25.2 (where the rail is moving at constant speed), what can you say about the power input due to the person pulling on the rail and the power dissipated in the resistance?

A) Power input from pull = power dissipated in R
B) Power input from pull > power dissipated in R
C) Power input from pull < power dissipated in R

1d) The electric generator as shown in the reading generates electricity by:

A) rotating a loop inside a magnetic field
B) moving a magnet in and out of a loop
C) sliding a loop over a magnet
D) running current through a loop in a magnetic field

1e) The magnetic flux through a loop:

A) is proportional to the number of magnetic field lines going through it
B) depends just on the B field going through the loop
C) is maximized when the B field lines in the plane of the loop
D) is zero when the B field is perpendicular to the plane of the loop
E) doesn't depend on the direction of the B field

1f) According to Lenz's Law, the induced B field (due to the induced current) will:

A) be in the opposite direction of the existing B field
B) be in the same direction as the existing B field
C) be in the same direction as the change in the existing B field
D) be in the opposite direction of the change in the existing B field

1g) A stationary coil experiences a doubling of its magnetic field (no change in direction of the field) in a time T and has a given induced EMF. If the same change were to have happened in half the time (T/2), the induced EMF would have been:

A) half as large
B) the same
C) twice as large
D) one-fourth as large
E) four times as large

1h) Eddy currents:

A) make it hard to pull a nonmagnetic material through a magnetic field
B) make it hard to pull a magnetic material through a magnetic field
C) speed up a magnetic material moving through a magnetic field
D) speed up a nonmagnetic material moving through a magnetic field

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PHYS 102 Study Guide - Midterm Guide: Magnetic Flux, Electric Flux, Dipole Antenna

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