charge of electron

A magnetic ﬁeld exerts a force on a charged particle:

1 always
2 never
3 if the particle is moving across the ﬁeld lines
4 if the particle is moving along the ﬁeld lines
5 if the particle is at rest

The magnetic force on a charged particle is in the direction of its velocity if:

1 it is moving in the direction of the ﬁeld
2 it is moving opposite to the direction of the ﬁeld
3 it is moving perpendicular to the ﬁeld
4 it is moving in some other direction
5 never

At any point the magnetic ﬁeld lines are in the direction of:

1 the magnetic force on a moving positive charge
2 the magnetic force on a moving negative charge
3 the velocity of a moving positive charge
4 the velocity of a moving negative charge
5 none of the above

An electron is moving north in a region where the magnetic ﬁeld is south. The magnetic force exerted on the electron is:

1 zero
2 up
3 down
4 east
5 west

A magnetic ﬁeld CANNOT:

1 exert a force on a charged particle
2 change the velocity of a charged particle
3 change the momentum of a charged particle
4 change the kinetic energy of a charged particle
5 change the trajectory 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:

1 0.5
2 1
3 2
4 4
5 8

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:

1 up
2 down
3 north
4 south
5 not at all

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:

1 upward
2 downward
3 to the right as seen from the electron source
4 to the left as seen from the electron source
5 not at all

An electron travels due north through a vacuum in a region of uniform magnetic ﬁeld n B that is also directed due north. It will:

1 be unaﬀected by the ﬁeld
2 speed up
3 slow down
4 follow a right-handed corkscrew path
5 follow a left-handed corkscrew path

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:

1 identical
2 equal in magnitude but opposite in direction
3 in the same direction and diﬀering in magnitude by a factor of 1840
4 in opposite directions and diﬀering in magnitude by a factor of 1840
5 equal in magnitude but perpendicular to each other.

J. J. Thomson’s experiment, involving the motion of an electron beam in mutually perpendicular E and B ﬁelds, gave the value of:

1 mass of an electron
2 charge of an electron
3 Earth’s magnetic ﬁeld
4 charge/mass ratio for electrons
5 Avogadro’s number

A charge is accelerated from rest through a potential difference V and then enters a uniform magnetic field oriented perpendicular to its path. The field deflects the particle into a circulararc of radius R. If the accelerating potential is tripled to 3V, what will be the radius of the circular arc?

1 9R
2 3R
3 √3R
4 R/3
5 R/9

Ions having equal charges but masses of Mand 2Mare accelerated through the same potential difference and then enter a uniform magnetic field perpendicular to their path. If the heavier ions follow a circular arc of radius R, what is the radius of the arc followed by the lighter?

1 4R
2 3R
3 2√R
4 R/√2
5 R/2

Which one of the following statements concerning the magnetic force on a charged particle in a magnetic field is true?

1 It is a maximum if the particle is stationary.
2 It is zero if the particle moves perpendicular to the field.
3 It is a maximum if the particle moves parallel to the field.
4 It acts in the direction of motion for a positively charged particle.
5 It depends on the component of the particle's velocity that is perpendicular to the field.

Complete the following statement: The magnitude of the magnetic force that acts on a charged particle in a magnetic field is independent of

1 the sign of the charge.
2 the magnitude of the charge.
3 the magnitude of the magnetic field.
4 the direction of motion of the particle.
5 the velocity components of the particle.

A charged particle is moving in a uniform, constant magnetic field. Which one of the following statements concerning the magnetic force exerted on the particle is false?

1 It does no work on the particle.
2 It increases the speed of the particle.
3 It changes the velocity of the particle.
4 It can act only on a particle in motion.
5 It does not change the kinetic energy of the particle.

Which one of the following statements best explains why a constant magnetic field can do no work on a moving charged particle?

1 The magnetic field is conservative.
2 The magnetic force is a velocity dependent force.
3 The magnetic field is a vector and work is a scalar quantity.
4 The magnetic force is always perpendicular to the velocity of the particle.
5 The electric field associated with the particle cancels the effect of the magnetic field on the particle

An electron traveling due north enters a region that contains a uniform magnetic field that points due east. In which direction will the electron be deflected?

1 east
2 west
3 down
4 up