Exam 4 Physics

( I ) Find the direction of the force on a negative charge for each diagram shown, where v ( green ) is the velocity of the charge and B ( blue ) is the direction of the magnetic field . ( x means the vector points inward . O means it points outward , toward you . )

(a) none (b) down (c) up (d) in (e) left (f) left

What is the magnitude of the magnetic force acting on the proton ? A proton ( q = 1.60x10^-19 C , m = 1.67x10^-27 kg ) moves in a uniform magnetic field B = ( 0.550 T ) i . At t = 0 the proton has velocity components vx = 1.50x10^5 m / s , vy = 0 , and vz = 2.30 × 10^5 m / s .

2.024x10^-14N j

Two positive point charges move side by side in the same direction with the same constant velocity . What is the direction of the magnetic force that the upper point charge exerts on the lower one ? A. toward the upper point charge ( the force is attractive ) B. away from the upper point charge ( the force is repulsive ) C. in the direction of the velocity D. opposite to the direction of the velocity E. none of the above

A)

12.43 ) The coil whose lengthwise cross section is shown in the accompanying figure carries a current I and has N evenly spaced turns distributed along the length l. Evaluate B dl for the paths indicated .

A. 3MoI B. 0 C. 7MoI D. -2MoI

An electron moving at 4.00 × 103m/s in a 1.25-T magnetic field experiences a magnetic force of 1.40 × 10−16 N. What angle does the velocity of the electron make with the magnetic field? There are two answers.

Angle= 10.1* and 169.9*

The figure shows , in cross section , three conductors that carry currents perpendicular to the plane of the figure . If the currents . h , and I all have the same magnitude , for which path ( s ) is / are the line integral of the magnetic field equal to zero ? A path a only B. paths a and c C. paths band d D. paths a , b , c , and d E. depends on whether the integral goes clockwise or counterclockwise around the path What is the line integral B dl for the path b ? The integral involves going around the path in the counterclockwise direction . What is the line integral B dl for the path c ? The integral involves going around the path in the counterclockwise direction .

B. path b= -MoI1 path c=Mo(I2-I1)

A + 7.00 μC point charge is moving at a constant 9.00 × 10 ^6 m / s in the + y direction , relative to a reference frame . At the instant when the point charge is at the origin of this reference frame , find the magnetic - field vector B it produces at x = 0.500m , y = 0 , z = 0 .

B=2.52x10^7 T (-k)

12.52 ) A solenoid is 40 cm long , has a diameter of 3.0 cm , and is wound with 500 turns . If the current through the windings is 4.0 A what is the magnetic field at a point on the axis of the solenoid that is at the center of the solenoid .

B=6.3x10^-3T

B Field From Current Element

B=IxMo/4pi integral -a to a (dy/(x^2+y^2)^3/2 (-k))

12.18 ) What is the magnetic field at P due to the current / in the wire shown ?

B=MoI/4pi(1/a-1/b) (k) (out)

Field from a solenoid , along the axis of the solenoid

B=MoIN/2L (sintheta2-sintheta1)j

Field from an infinite solenoid using Ampere's Law .

B=MoIN/L

B Field From Wire Lopp

B=MoIa^2/2(sqrtx^2+a^2)^3/2

A beam of electrons ( which have negative charge ) is coming straight toward you . You place a magnet as shown directly above the beam . The magnetic field B from the magnet points straight down . Which way will the electron beam deflect ? A. upward B. downward C. to the left D. to the right E. It won't deflect at all

C fingers = direction of magnetic field thumb = direction of motion of chrlarged particle palm = direction of force on + ve charge opposite face pf palm j force on negative charge now if you points direction of thumb ( direction of electron beam) towards you and fingers points ( downward( direction of magnetic field) then the opposite face of your palm ( to the left ) points direction of applied force on electron.

How should the strength of the magnetic field at every point be reflected in the magnetic field lines ? Carefully draw the magnetic field lines for the bar magnet shown . Be sure to draw the lines so that they include information about the strength and direction of the field both inside and outside the magnet . Based on the magnet field lines you have drawn , rank the magnitude of the magnetic field points A - E .

C>D>E>B>A

A particle with a positive charge moves in the xz - plane as shown . The magnetic field is in the positive z - direction . The magnetic force on the particle is in A. the positive x - direction . B. the negative x - direction . C. the positive y - direction . D. the negative y - direction . E. none of these .

D The charge is positive so the force is in the same direction as the vector product V x B. from the RHR this direction is along negative y axis

A horizontal wire carries a current and is in a vertical magnetic field . What is the direction of the force on the wire ? a ) left b ) right c ) zero d ) into the page e ) out of the page

E) out of the page

The current loop shown in the accompanying figure lies in the plane of the page, as does the magnetic field. Determine the net force and the net torque on the loop if I = 10 A and B = 1.5 T.

Fnet=0N Tnet=.104Nm (-i)

Find the current through a loop needed to create a maximum torque of 9.0 N · m. The loop has 50 square turns that are 15.0 cm on a side and is in a uniform 0.800-T magnetic field.

I=10A max torque=T=NIAB orig torque=T=NIABsintheta

A 200-turn circular loop of radius 50.0 cm is lying flat on the ground with its current 100A circulating counterclockwise (when viewed from above) in a location where Earth's field is north, but at an angle 45.0° below the horizontal and with a strength of 6.0 × 10−5T, with its axis on an east-west line. What are the direction and magnitude of the torque on the loop?

T=.666Nm east

The 20.0 cm by 35.0 cm rectangular circuit shown in the figure is hinged alongside ab . It carries a clockwise 5.00 A current and is located in a uniform 1.20 T magnetic field oriented perpendicular to two of its sides , as shown . Calculate only the force that exert the torque , and find the torque about hinge axis ab .

T=MXB and M=IA T=.42Nm (-j) F=(IL)XB F=1.20N (k)

Two long , straight wires are oriented perpendicular to the xy - plane . They carry currents of equal magnitude I in opposite directions as shown . At point P , the magnetic field due to these currents is in a ) + x b ) + y c ) zero d ) - x e ) - y

a) (study manipulating it to be zero)

A 5.0-m section of a long, straight wire carries a current of 10 A while in a uniform magnetic field of magnitude 8.0 × 10−3T. Calculate the magnitude of the force on the section if the angle between the field and the direction of the current is (a) 45°; (b) 90°; (c) 0°; or (d) 180°

a) .283N b) .40N c) 0N d) 0N

12.46 ) Below is a cross - section of a long , hollow , cylindrical conductor of inner radius r1 = 3.0 cm and outer radius of r₂ = 5.0 cm . A 50 - A current is distributed uniformly over the cross - section , flows into the page . Calculate the magnetic field at a ) r = 20 cm b ) r = 4.0 cm c ) r = 6.0 cm

a) B=0 b) 1.09x10^-4T clockwise c) 1.67x10^-4T clockwise

12.16 ) A 10 A current flows through the wire shown . What is the magnitude of the magnetic field due to a 0.5 - mm segment of wire as measured at ( a ) point A and ( b ) point B ?

a) B=5.56x10^-7T b) B=3.33x10^-7T

(a) A dc power line for a light-rail system carries 1000 A at an angle of 30.0º to Earth's 5.0 × 10−5T field. What is the force on a 100-m section of this line? (b) Discuss practical concerns this presents, if any

a) F=2.5 N b) Negligible force therefore no concerns

The current through a circular wire loop of radius 10 cm is 5.0 A. (a) Calculate the magnetic dipole moment of the loop. (b) What is the torque on the loop if it is in a uniform 0.20-T magnetic field such that µ and B are directed at 30° to each other? (c) For this position, what is the potential energy of the dipole?

a) M=.157 Am^2 b) T=.0157 Nm c) U= .0272 J

a ) What voltage will accelerate electrons to a speed of 6.00 x 10-7 m / s ? b ) Find the radius of curvature of the path of a proton accelerated through this potential in a 0.500 T field and compare this with the radius of curvature of an electron accelerated through the same potential .

a) V= mv^2/2q V=1.02x10^-24V b) qVB=mv^2/r , rp/re=? r=2.93x10^-16m (the ratio of the radius of the proton of the electron is 42)

What is the direction of the magnetic field that produces the magnetic force on a positive charge as shown in each of the three cases, assuming B → is perpendicular to →v ?

a) in b) left c) out

What is the direction of the magnetic field that produces the magnetic force shown on the currents in each of the three cases, assuming B → is perpendicular to I

a) in b) left c) out

What is the direction of the magnetic force on the current in each case?

a) left b) in c) up d) zero

What is the direction of the magnetic force on a positive charge that moves as shown in each of the six cases?

a) left b) in c) up d) zero e) right f) down

What is the direction of the magnetic force on the current in each of the six cases?

a) left b) in c) up d) zero e) right f) down

What is the direction of the velocity of a positive charge that experiences the magnetic force shown in each of the three cases, assuming it moves perpendicular to B?

a) left b) out c) up

What is the direction of the magnetic field that produces the magnetic force on a negative charge as shown in each of the three cases, assuming B → is perpendicular to →v ?

a) out b) right c) in

What is the direction of the magnetic force on a negative charge that moves as shown in each of the six cases?

a) right b) out c) down d) zero e) left f) up

What is the direction of the velocity of a negative charge that experiences the magnetic force shown in each of the three cases, assuming it moves perpendicular to B?

a) right b) in c) down

An alpha-particle (m = 6.64 × 10−27 kg, q = 3.2 × 10−19 C) travels in a circular path of radius 25 cm in a uniform magnetic field of magnitude 1.5 T. (a) What is the speed of the particle? (b) What is the kinetic energy in electron-volts? (c) Through what potential difference must the particle be accelerated in order to give it this kinetic energy?

a) v=1.81x10^7 m/s b) KE= 6.77x10^6 eV c) Delta V=3.39x10^6 V

Two particles of the same mass enter a magnetic field with the same speed and follow the paths shown . Which particle has the bigger charge ? a ) A b ) B c ) Both charges are equal d ) It is not possible to tell

b) q=mv/rB

A horizontal wire carries a current and is in a vertical magnetic field . What is the direction of the force on the wire ? a ) left b ) right c ) zero d ) into the page e ) out of the page

c) zero

A rectangular current loop is in a uniform magnetic field . What is the direction of the net force on the loop ? a ) + x b ) + y c ) zero d ) -x e ) -y

c) zero

What is the direction of the magnetic field at the center ( point P ) of the square loop of current ? a ) left . b ) right c ) zero d ) into the page e ) out of the page

e) out of the page

Find the magnetic field both inside and outside of the conductor as a function of a distance from the center of the cylinder .

inside conductor B=MoI/2pi(r/R^2) outside conductor B=MoI/2pir