two long parallel wires 20 cm apart carry currents of 5a and 8a in the same direction. is there any...
TRANSCRIPT
Two long parallel wires 20 cm apart carry currents of 5A and 8A in the same direction. Is there any point between the two wires where the magnetic field is zero?
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1. Yes, midway between the wires.
2. Yes, 12 cm from the 5A wire.
3. Yes, 7.7 cm from the 5A wire.
4. No.
A rectangular coil (0.20 m x 0.80 m) has 200 turns and is in a uniform magnetic field of 0.30 T. If the orientation of the coil is varied through all possible positions, the maximum torque on the coil by magnetic forces is 0.080 N-m. What is the current in the coil?
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1. 5.0 mA
2. 1.7 A
3. 8.3 mA
4. 1.0 A
A circular coil (radius = 0.40 m) has 160 turns and is in a uniform magnetic field. If the orientation of the coil is varied through all possible positions, the maximum torque on the coil by magnetic forces is 0.16 N-m when the current in the coil is 4.0 mA. What is the magnitude of the magnetic field?
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1. 0.37 T
2. 1.6 T
3. 0.50 T
4. 1.2 T
A high-voltage powerline 20 m above the ground carries a current of 2000 A. What is the magnetic field due to the current directly underneath the powerline? (µ 0 = 4∏ x 10-7 T-m/A)
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1. 20.0 µ T
2. 35.0 µ T
3. 14.0 mT
4. 0.3 T
A superconducting solenoid is to be designed to generate a magnetic field of 10 T. If the solenoid winding has 2000 turns/meter, what is the required current? (µ 0 = 4∏ x 10-7 A-m/T)
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1. 1000 A
2. 1990 A
3. 3980 A
4. 5000 A
An incredible amount of electrical energy passes down the funnel of a large tornado every second. Measurements taken in Oklahoma at a distance of 9 km from a large tornado showed an almost constant magnetic field of 1.5 x 10-8 T associated with the tornado. What was the average current -going down the funnel? (µ 0 = 4∏ x 10-7 A-m/T)
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1. 150 A
2. 250 A
3. 350 A
4. 500 A
Superconductors are capable of carrying very large currents with no resistance. If a superconducting wire is formed into a solenoid of length 50 cm with 500 turns, what is the magnetic field inside the solenoid when the current is 104 A? ( µ 0 = 4∏ x 10-7 A-m/T)
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1. 1.25 T
2. 2.50 T
3. 6.28 T
4. 12.6 T
In a mass spectrometer, an ion will have a smaller radius for its circular path if
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1. its speed is greater
2. its mass is greater
3. its charge is greater
4. the magnetic field is weaker
A current in a long, straight wire produces a magnetic field, and these magnetic field lines
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1. go out from the wire to infinity
2. come in from infinity to the wire
3. form circles which pass through the wire
4. form circles which go around the circle
Consider two long, straight parallel wires, each carrying a current I. If the currents are flowing in opposite directions
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1. the two wires will attract each other
2. the two wires will repel each other
3. the two wires will exert a torque on each other
4. neither wire will exert a force on the other
When a magnetic field causes a charged particle to move in a circular path, the only quantity listed below which the magnetic force changes significantly as the particle goes around in a circle is the particle's
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1. energy
2. momentum
3. radius for the circle
4. time to go around the circle once
A superconducting wire carries a current of 104 A. Find the magnetic field at a distance of 1.0 m from the wire. ( µ 0 = 4∏ x 10-7 A-m/T)
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1. 2.0 x 10-3 T
2. 8.0 x 10-3 T
3. 1.6 x 10-2 T
4. 3.2 x 10-2 T
There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper. If the magnetic field B is toward the right, and if each side of the loop has length L, then the net magnetic torque acting on the loop is
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1. 2ILB
2. ILB
3. IBL2
4. zero
A galvanometer can be used to make either an ammeter or a voltmeter. Under which condition will the deflection of the needle be greatest when a very small current flows through the device?
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1. the current goes through the original galvanometer.
2. the current goes through the voltmeter.
3. the voltmeter and the original galvanometer will give the same deflection if the current is the same.
4. the current goes through the ammeter.
There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper. If the magnetic field B is toward the right, and if each side of the loop has length L, then the net magnetic force acting on the loop is
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1. 2ILB
2. ILB
3. IBL2
4. zero
An electron which moves with a speed of 3 x 104 m/s perpendicular to a uniform magnetic field of 0.40 T experiences a force of what magnitude? (qe = 1.6 x 10-19 C)
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1. 4.8 x 10-14 N
2. 19.2 x 10-16 N
3. 2.2 x 10-24 N
4. zero
A 2.0 m wire segment carrying a current of 0.60 A oriented parallel to a uniform magnetic field of 0.50 T experiences a force of what magnitude?
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1. 6.7 N
2. 0.30 N
3. 0.15 N
4. zero
A proton moving with a speed of 3 x 105 m/s perpendicular to a uniform magnetic field of 0.20 T will follow which of the paths described below? (qe = 1.6 x 10-19 C and mp = 1.67 x 10-27 kg)
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1. a straight line path
2. a circular path of 1.5 cm radius
3. a circular path of 3.0 cm radius
4. a circular path of 0.75 cm radius
If a deuteron, with the same charge but twice the mass of a proton, were to move with a speed of 3 x 105 m/s perpendicular to a uniform magnetic field of 0.20 T, it would follow which of the paths described below? (qp = 1.6 x 10-19 C and md = 3.34 x 10-27 kg)
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1. a straight line path
2. a circular path of 1.5 cm radius
3. a circular path of 3.0 cm radius
4. a circular path of 0.75 cm radius
If a proton is released at the equator and falls toward the Earth under the influence of gravity, the magnetic force on the proton will be toward the
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1. north
2. south
3. east
4. west
A stationary positive charge +Q, located in a magnetic field B, which is directed toward the right as indicated. The direction of the magnetic force on Q is
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1. toward the right
2. up
3. down
4. there is no magnetic force
A wire is lying horizontally in the north-south direction and the horizontal magnetic field is toward the east. There are some positive charges in the wire moving north and equal number of negative charges moving south. The direction of the force on the wire will be
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1. east
2. down, into the page
3. up, out of the page
4. there is no magnetic force
There is a magnetic force on a particle. It is possible that the particle is
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1. uncharged
2. stationary
3. moving in the direction of the magnetic field
4. not part of a wire
Electrical charges and magnetic poles have many similarities. However, one difference between the two is that
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1. opposite magnetic poles repel
2. one magnetic pole cannot create magnetic poles in other materials
3. a magnetic pole cannot be isolated
4. magnetic poles do not produce magnetic fields
Two singly ionized isotopes, X and Y, of the same element move with the same speed perpendicular to a uniform magnetic field. Isotope X follows a path of radius 3.35 cm while isotope Y moves along a 3.43 cm radius path. What is the ratio of the two isotope masses, mX /mY ?
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1. 0.977
2. 1.023
3. 1.048
4. 0.954
A 10 ohm, 25 mA galvanometer is to be converted into an ammeter which reads 5 A at a full scale deflection. What resistance should be placed in parallel with the galvanometer coil?
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1. 2.5 ohms
2. 0.5 ohms
3. 0.25 ohms
4. 0.05 ohms
A proton which moves perpendicular to a magnetic field of 1.2 T in a circular path of 0.08 m radius, has what speed? (qp = 1.6 x 10-19 C and mp = 1.67 x 10 -27 kg)
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1. 3.4 x 106 m/s
2. 4.6 x 106 m/s
3. 9.6 x 106 m/s
4. 9.2 x 106 m/s
A 10 ohm, 25 mA galvanometer is to be converted into a voltmeter which reads 20 V at full scale deflection. What resistance should be placed in series with the galvanometer coil?
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1. 810 ohms
2. 790 ohms
3. 500 ohms
4. 450 ohms
A 10 ohm, 15 mA galvanometer is converted into an ammeter by placing a 1.5 x 10-2 ohm shunt in parallel with the galvanometer coil. What is the maximum scale reading on the galvanometer?
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1. 25.0 A
2. 15.0 A
3. 10.0 A
4. 5.0 A
A circular loop carrying a current of 2.0 A is oriented in a magnetic field of 3.5 T. The loop has an area of 0.12 m2 and is mounted on an axis, perpendicular to the magnetic field, which allows the loop to rotate. If the plane of the loop is oriented parallel to the field, what torque is created by the interaction of the loop current and the field?
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1. 58 N-m
2. 6.8 N-m
3. 0.84 N-m
4. 0.17 N-m
A circular loop carrying a current of 2.0 A is oriented in a magnetic field of 3.5 T. The loop has an area of 0.12 m2 and is mounted on an axis, perpendicular to the magnetic field, which allows the loop to rotate. What is the torque on the loop when its plane is oriented at a 37° angle to the field?
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1. 46.0 N-m
2. 0.67 N-m
3. 0.51 N-m
4. 0.10 N-m
A horizontal wire of length 3.0 m carries a current of 6.0 A and is oriented so that the current direction is 50° S of W. The horizontal component of the earth's magnetic field is due north at this point and has a strength of 0.14 x 10-4 T. What is the direction of the force on the wire?
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1. out of the earth's surface
2. toward the earth's surface
3. due east
4. 40° S of E
A current carrying wire of length 50 cm is positioned perpendicular to a uniform magnetic field. If the current is 10.0 A and it is determined that there is a resultant force of 3.0 N on the wire due to the interaction of the current and field, what is the magnetic field strength?
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1. 0.6 T
2. 1.50 T
3. 1.85 x 103 T
4. 6.7 x 103 T
A horizontal wire of length 3.0 m carries a current of 6.0 A and is oriented so that the current direction is 50° S of W. The horizontal component of the earth's magnetic field is due north at this point and has a strength of 0.14 x 10-4 T. What is the size of the force on the wire?
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1. 0.28 x 10-4 N
2. 2.5 x 10-4 N
3. 1.9 x 10-4 N
4. 1.6 x 10-4 N
An electron moves across the earth's equator at a speed of 2.5 x 106 m/s and in a direction 35° N of E. At this point the earth's magnetic field has a direction due north, is parallel to the surface, and has a value of 0.10 x 10-4 T. What is the direction of the force acting on the electron at this instant?
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1. due west
2. into the earth's surface
3. out of the earth's surface
4. due south
A proton is released such that it has an initial speed of 4 x 105 m/s from left to right across the page. A magnetic field of 1.2 T is present at an angle of 30° to the horizontal direction (or positive x-axis). What is the magnitude of the force experienced by the proton? (qp = 1.6 x 10-19 C)
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1. 4.8 x 10-25 N
2. 1.3 x 10-19 N
3. 3.8 x 10-14 N
4. 7.5 x 103 N
An electron moves across the earth's equator at a speed of 2.5 x 106 m/s and in a direction 35° N of E. At this point the earth's magnetic field has a direction due north, is parallel to the surface, and has a value of 0.10 x 10-4 T. What is the magnitude of the force acting on the electron due to its interaction with the earth's magnetic field? (qe = -1.6 x 10-19 C)
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1. 5.1 x 10-18 N
2. 4.0 x 10-18 N
3. 3.3 x 10-18 N
4. 2.3 x 10-18 N
A proton is released such that its initial velocity is from right to left across this page. The proton's path, however, is deflected in a direction toward the bottom edge of the page due to the presence of a uniform magnetic field. What is the direction of this field?
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1. out of the page
2. into the page
3. from bottom edge to top edge of the page
4. from right to left across the page
Geo-physicists today generally attribute the existence of the earth's magnetic field to which of the following?
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1. convection currents within the liquid interior
2. iron ore deposits in the crust
3. nickel-iron deposits in the crust
4. solar flares
The term magnetic declination refers to which of the following?
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1. angle between earth's magnetic field and earth's surface
2. earth's magnetic field strength at the equator
3. tendency for earth's field to reverse itself
4. angle between directions to true north and magnetic north
The magnetic field of the earth is believed responsible for which of the following?
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1. deflection of both charged and uncharged cosmic rays
2. deflection of charged cosmic rays
3. ozone in the upper atmosphere
4. solar flares
Assume that a uniform magnetic field is directed into this page. If an electron is released with an initial velocity directed from the bottom edge to the top edge of the page, which of the following describes the direction of the resultant force acting on the electron?
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1. out of the page
2. to the right
3. to the left
4. into the page
A current in a solenoid with N turns creates a magnetic field at the center of that loop. The field strength is directly proportional to which of the following?
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1. number turns in loop
2. current strength
3. both of the choices are valid
4. none of the choices are valid
A circular current loop is placed in an external magnetic field. How is the torque related to the radius of the loop?
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1. directly proportional to radius
2. inversely proportional to radius
3. directly proportional to radius squared
4. inversely proportional to radius squared
The path of a charge particle moving parallel to a uniform magnetic field will be which of the following?
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1. straight line
2. circle
3. ellipse
4. parabola
The current in a long wire creates a magnetic field in the region around the wire. How is the strength of that field at a given distance, r, from the wire center related to the magnitude of the field?
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1. field directly proportional to r
2. field inversely proportional to r
3. field directly proportional to r2
4. field inversely proportional to r2
The direction of the force on a current carrying wire located in an external magnetic field is which of the following?
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1. perpendicular to the current
2. perpendicular to the field
3. both of the choices are valid
4. none of the choices are valid
A current in a solenoid coil creates a magnetic field inside that coil. The field strength is directly proportional to which of the following?
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1. coil area
2. current
3. both current and coil area
4. none of these
Which of the following devices makes use of an electromagnet?
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1. loudspeaker
2. galvanometer
3. both of the choices
4. none of the choices
The magnetic domains in a non-magnetized piece of iron are characterized by which orientation?
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1. parallel to the magnetic axis
2. anti-parallel to the magnetic axis
3. random
4. perpendicular to the magnetic axis
The force on a charged particle created by its motion in a magnetic field is maximum at what angle between the particle velocity and field?
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1. zero
2. 180°
3. 90°
4. 45°
A solenoid with 500 turns, 0.10 m long, carrying a current of 4.0 A and with a radius of 10-2 m will have what strength magnetic field at its center? (magnetic permeability in empty space µ 0 = 4∏ x 10 -7 T-m/A)
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1. 31 x 10-4 T
2. 62 x 10-4 T
3. 125 x 10-4 T
4. 250 x 10-4 T
The force exerted on a current carrying wire located in an external magnetic field is directly proportional to which of the following?
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1. current strength
2. field strength
3. both of the choices
4. none of the choices are valid
A thin copper rod 1.0 m long has a mass of 50 grams. What is the minimum current in the rod that would allow it to "float" in a magnetic field of 0.1T?
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1. 1.23 A
2. 2.45 A
3. 4.9 A
4. 9.8 A
A 100 m long wire carrying a current of 4.0 A will be accompanied by a magnetic field of what strength at a distance of 0.05 m from the wire? (magnetic permeability in empty space µ 0 = 4∏ x 10-7 T-m/A)
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1. 4.0 x 10-5 T
2. 2.0 x 10-5 T
3. 1.6 x 10-5 T
4. zero
Two parallel conductors each of 0.5 m length, separated by 5 x 10-3 m and carrying 3.0 A in opposite directions, will experience what type and magnitude of mutual force? (magnetic permeability in empty space µ 0 = 4∏ x 10-7 T-m/A)
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1. attractive, 0.06 x 10-4 N
2. repulsive, 0.60 x 10-4 N
3. attractive, 1.8 x 10-4 N
4. repulsive, 1.8 x 10-4 N
At the Fermilab accelerator in Weston, Illinois, protons with momentum 4.8 x 10-16 kg-m/s are held in a circular orbit of radius 1 km by an upward magnetic field. What upward B-field must be used to maintain the protons in this orbit? (qp = 1.6 x 10-19 C)
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1. 1 T
2. 2 T
3. 3 T
4. 4 T
An electron moves through a region of crossed electric and magnetic fields. The electric field E = 1000 V/m and is directed straight down. The magnetic field B = 0.4 T and is directed to the left. For what velocity v of the electron into the paper will the electric force exactly cancel the magnetic force?
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1. 2500 m/s
2. 4000 m/s
3. 5000 m/s
4. 8000 m/s
Niobium metal becomes a superconductor (with electrical resistance equal to zero) when cooled below 9 K. If superconductivity is destroyed when the surface magnetic field exceeds 0.1 T, determine the maximum current a 4-mm diameter niobium wire can carry and remain superconducting. ( µ 0 = 4∏ x 10-7 A-m/T)
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1. 125 A
2. 250 A
3. 500 A
4. 1000 A
A proton, mass 1.67 x 10-27 kg and charge +1.6 x 10-19
C, moves in a circular orbit perpendicular to a uniform magnetic field of 0.75 T. Find the time for the proton to make one complete circular orbit.
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1. 4.3 x 10-8 s
2. 8.7 x 10-8 s
3. 4.9 x 10-7 s
4. 9.8 x 10-7 s