Units of a magnetic field might be:
D. kg/C�s
In the formula F = qv � B :
E. F must be perpendicular to both v and B
An electron moves in the negative x direction, through a uniform magnetic field in the negative y direction. The magnetic force on the electron is:
E. in the negative z direction
At any point the magnetic field lines are in the direction of:
E. none of the above
The magnetic force on a charged particle is in the direction of its velocity if:
E. never
A magnetic field exerts a force on a charged particle:
C. if the particle is moving across the field lines
The direction of the magnetic field in a certain region of space is determined by firing a test charge into the region with its velocity in various directions in different trials. The field direction is:
A. one of the directions of the velocity when the magnetic force is zero
An electron is moving north in a region where the magnetic field is south. The magnetic force exerted on the electron is:
A. zero
A magnetic field CANNOT:
D. change the kinetic energy of a charged particle
A proton (charge e), traveling perpendicular to a magnetic field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. The ratio of their speeds, vproton/valpha, is:
C. 2
A hydrogen atom that has lost its electron is moving east in a region where the magnetic field is directed from south to north. It will be deflected:
A. up
A beam of electrons is sent horizontally down the axis of a tube to strike a fluorescent screen at the end of the tube. On the way, the electrons encounter a magnetic field directed vertically downward. The spot on the screen will therefore be deflected:
C. to the right as seen from the electron source
An electron (charge = ?1.6 � 10?19 C) is moving at 3 �105 m/s in the positive x direction. A magnetic field of 0.8T is in the positive z direction. The magnetic force on the electron is:
D. 4 � 10^?14 N, in the positive y direction
At one instant an electron (charge = ?1.6�10^?19 C) is moving in the xy plane, the components of its velocity being vx = 5�10^5 m/s and vy = 3� 10^5 m/s. A magnetic field of 0.8T is in the positive x direction. At that instant the magnitude of the magneti
C. 3.8 � 10^?14 N
16 An electron travels due north through a vacuum in a region of uniform magnetic field B that is also directed due north. It will:
A. be unaffected by the field
At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, it subsequent motion is:
B. counterclockwise around a circle in the xy plane
A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:
B. the charge is negative and slowing down
An electron and a proton each travel with equal speeds around circular orbits in the same uniform magnetic field, as shown in the diagram (not to scale). The field is into the page on the diagram. Because the electron is less massive than the proton and b
A. the electron travels clockwise around the smaller circle and the proton travels counterclockwise around the larger circle
An electron is launched with velocity v in a uniform magnetic field B. The angle ? between v and B is between 0 and 90?. As a result, the electron follows a helix, its velocity vector v returning to its initial value in a time interval of:
A. 2?m/eB
An electron and a proton are both initially moving with the same speed and in the same direction at 90? to the same uniform magnetic field. They experience magnetic forces, which are initially:
B. equal in magnitude but opposite in direction
An electron enters a region of uniform perpendicular E and B fields. It is observed that the velocity v of the electron is unaffected. A possible explanation is:
D. v is perpendicular to both E and B and has magnitude E/B
A charged particle is projected into a region of uniform, parallel, E and B fields. The force on the particle is:
B. at some angle < 90? with the field lines
A uniform magnetic field is in the positive z direction. A positively charged particle is moving in the positive x direction through the field. The net force on the particle can be made zero by applying an electric field in what direction?
B. Negative y
An electron is traveling in the positive x direction. A uniform electric field E is in the negative y direction. If a uniform magnetic field with the appropriate magnitude and direction also exists in the region, the total force on the electron will be z
C. into the page
An ion with a charge of +3.2�10^?19 C is in a region where a uniform electric field of 5�10^4 V/m is perpendicular to a uniform magnetic field of 0.8T. If its acceleration is zero then its speed must be:
D. 6.3 � 10^4 m/s
The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:
A. positive
Electrons (mass m, charge ?e) are accelerated from rest through a potential difference V and are then deflected by a magnetic field B that is perpendicular to their velocity. The radius of the resulting electron trajectory is:
C. [ sqrt(2mV) / e ] / B
In a certain mass spectrometer, an ion beam passes through a velocity filter consisting of mutually perpendicular fields E and B. The beam then enters a region of another magneticfield B' perpendicular to the beam. The radius of curvature of the resulting
E. E/BB'
A cyclotron operates with a given magnetic field and at a given frequency. If R denotes the radius of the final orbit, the final particle energy is proportional to:
C. R^2
J. J. Thomson's experiment, involving the motion of an electron beam in mutually perpendicular E and B fields, gave the value of:
D. charge/mass ratio for electrons