Electromagnetism Flashcards
PROBLEMS AND OBJECTIVE TYPE QUESTIONS
- An electric field is most directly
related to:
A. the momentum of a test charge
B. the kinetic energy of a test charge
C. the potential energy of a test
charge
D. the force acting on a test charge
- D. the force acting on a test charge
- An electron is accelerated from rest
through a potential difference V. Its
final speed is proportional to:
A. V
C. V»
B. V«
D. 1/V
B. V«
- The magnetic force on a charged
particle is in the direction of its
velocity if:
A. it is moving in the direction of the
field
B. it is moving opposite to the
direction of the field
C. it is moving perpendicular to the
field
D. never
D. never
- Charge Q is distributed uniformly
throughout an insulating sphere of
radius R. The magnitude of the
electric field at a point R/2 from the
center is:
A. Q/4 πε0R»
B. Q/πε0R»
C. 3Q/4ε0R»
D. Q/8πε0R»
D. Q/8πε0R»
- 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:
A. 1/R
C. R
B. R»
D. R»>
B. R»
- Choose the correct statement
concerning electric field lines:
A. field lines may cross
B. field lines are close together
where the field is large
C. field lines point away from a
negatively charged particle
D. a charged pint particle released
from rest moves along a field line
B. field lines are close together
where the field is large
- The force acting on a pole of 3 Wb is
12 N. The magnetic intensity of the
magnetic field is
A. 4 N/Wb C. 12 N/Wb
B. 36 N/Wb D. 8 N/Wb
A. 4 N/Wb
- A particle with charge Q is placed
outside a large neutral conducting
sheet. At any point in the interior of
the sheet the electric field produced
by chares on the surface is directed:
A. toward the surface
B. away from the surface
C. toward Q
D. away from Q
C. toward Q
- An electron volt is:
A. the force acting on an electron in
a field of 1 N/C
B. the force required to move an
electron 1 meter
C. the energy gained by an electron
in moving through a potential
difference of 1 volt
D. the energy needed to move an
electron through 1 meter in any
electric field
. C. the energy gained by an
electron in moving through a
potential difference of 1 volt
- An EMF of one volt:
A. Cannot drive much current
through a circuit.
B. Represents a low resistance.
C. Can sometimes produce a large
current.
D. Drops to zero in a short time.
- C. Can sometimes produce a large
current.
- At any point the magnetic field lines
are in the direction of:
A. the magnetic force on a moving
positive charge
B. the magnetic force on a moving
negative charge
C. the velocity of a moving positive
charge
D. None of the above
- D. None of the above
- A positive electric pole:
A. Has a deficiency of electrons.
B. Has fewer electrons than the
negative pole.
C. Has an excess of electrons.
D. Has more electrons than the
negative pole.
- B. Has fewer electrons than the negative pole.
- Two-point particles, with charges of
q1 and q2, are placed a distance r
apart. The electric field is zero at a
point P between the particles on the
line segment connecting them. We
conclude that:
A. q1 and q2 must have the same
magnitude and sign
B. P must be midway between the
particles
C. q1 and q2 must have the same sign
but may have different
magnitudes
D. q1 and q2 must have equal
magnitudes and opposite signs
- C. q1 and q2 must have the same
sign but may have different
magnitudes
- A small single-phase transformer has
10.2 watts at no load. The core has a
volume of 750 cubic cm. The
maximum flux density is 10,000
gauss and the hysteresis constant of
the core is 5 x 10-4
. Using the
Steinmetz law to find the hysteresis,
determine the eddy current loss.
A. 4.55 W C. 5.55 W
B. 3.55 W D. 2.55 W
- A. 4.55 W
- A hollow conductor is positively
charged. A small uncharged metal
ball is lowered by a silk thread
through a small opening in the top of
the conductor and allowed to touch
surface. After the ball is removed, it
will have:
A. a positive charge
B. a negative charge
C. no appreciable charge
D. a charge whose sign depends on
what part of the inner surface it
touched
- C. no appreciable charge
- 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
B. the direction of the velocity when
the magnetic force is a maximum
C. the direction of the magnetic
force
D. perpendicular to the velocity
when the magnetic force is zero
- A. one of the directions of the
velocity when the magnetic
force is zero
- The reluctance of a non-magnetic
circuit is 12 units. How much flux
will be set up if surrounded by a coil
600 turns carrying a current of 3A?
A. 150 Wb C. 16.67 Wb
B. 50 Wb D. 200 Wb
- A. 150 Wb
21.If R is the distance from a magnetic
dipole, then the magnetic field it
produces is proportional to:
A. 1/R
C. R»
B. 1/R»
D. 1/R»>
D. 1/R»>
- A toroid with a square cross section
carries current i. The magnetic field
has its largest magnitude:
A. at the center of the hole
B. just inside the toroid at its inner
surface
C. just inside the toroid a its outer
surface
D. at any point inside (the field is
uniform)
- B. just inside the toroid at its inner
surface
- The equipotential surfaces associated
with a charged point particle are:
A. radially outward form the particle
B. vertical planes
C. horizontal planes
D. concentric spheres centered at the
particle
- D. concentric spheres centered at
the particle
- The outer surface of the cardboard
center of a paper towel roll:
A. is a possible Gaussian surface
B. cannot be a Gaussian surface
because it encloses no charge
C. cannot be a Gaussian surface
since it is an insulator
D. cannot be a Gaussian surface
because it is not a closed surface
- D. cannot be a Gaussian surface
because it is not a closed surface
- A magnetic circuit consists of silicon
steel of 3000 permeability and an air
gap. The length of the steel core is
10cm and the air gap is 2 cm. Both have the same cross section of 1.5 sq.
cm. A current of 1/2 ampere flows
through the windings to produce
2351 maxwells flux. How many turns
are there in the coil?
A. 4120 turns
B. 5000 turns
C. 2500 turns
D. 1250 turns
- B. 5000 turns
- A magnetic torque exerted on a flat
current-carrying loop of wire by a
uniform magnetic field
B
is:
A. maximum when the plane of the
loop is perpendicular to
B
B. maximum when the plane of the
loop is parallel to
B
C. dependent on the shape of the
loop for a fixed loop area
D. independent of the orientation of
the loop
- B. maximum when the plane of the
loop is parallel to
B
- A square loop of current-carrying
wire with edge length a is in the xy
plane, the origin being at its center.
Along which of the following lines
can be charge move without
experiencing a magnetic force?
A. x = 0, y = a/2
B. x = a/2, y = a/2
C. x = a/2, y = 0
D. x = 0, y = 0
- D. x = 0, y = 0
- A magnetic field exerts a force on a
charged particle:
A. always
B. never
C. if the particle is moving across
the field lines
D. if the particle is moving along the
field lines
- C. if the particle is moving across
the field lines
- Helmholtz coils are commonly used
in the laboratory because the
magnetic field between them:
A. can be varied more easily than
fields of other current
arrangements
B. is especially strong
C. nearly cancels Earth’s magnetic
field
D. is nearly uniform
- D. is nearly uniform
- Two spheres separated from each
other by 10m have charges of 0.001
coulomb and 0.003 coulomb
respectively. In between the two
spheres is a point of zero electric
field. What is the distance from the
0.001 coulomb sphere?
A. 6.34 m C. 7.78 m
B. 2.24 m D. 3.66 m
- D. 3.66 m
- An electron traveling north enters a
region where the electric field is
uniform and points north. The
electron:
A. speed up
B. slow down
C. veers east
D. veers west
- B. slow down
- Lines of the magnetic field produced
by a long straight wire carrying a
current are:
A. in the direction of the current
B. radially outward form the wire
C. radially inward toward the wire
D. circles that are concentric with
the wire
- D. circles that are concentric with
the wire
- An electron is moving north in a
region where the magnetic field is
south. The magnetic force exerted on
the electron is:
A. zero C. up
B. down D. east
- A. zero
- A uniform magnetic field is 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?
A. Positive y
B. Negative y
C. Positive x
D. Negative x
- B. Negative y
- The purpose of Milliken’s oil drop
experiment was to determine:
A. the mass of an electron
B. the charge of an electron
C. the ratio of charge to mass of an
electron
D. the sign of the charge on an
electron
- B. the charge of an electron
- Two electrons in a vacuum
experience a force of 2 x 10-15 N.
How far apart are the electrons?
A. 0.48 x 10-7 m
B. 2.84 x 10-12 m
C. 3.39 x 10-7 m
D. 5.05 x 10-12 m
- C. 3.39 x 10-7 m
- An electron is moving north in a
region where the magnetic field is
south. The magnetic force exerted on
the electron is:
A. zero C. up
B. down D. east
- A. zero
41.In an overhead straight wire, the
current is north. The magnetic field
due to this current, at our point of
observation, is:
A. east C. north
B. down D. west
- D. west
- 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
B. speed up
C. slow down
D. follow a right-handed corkscrew
path
- A. be unaffected by the field
- The relative permeability of a certain
silicon steel is 4500. A certain
magnetic loop consists of a silicon
steel of 10 cm square, 20 cm long
and an air gap of 1/4 cm. What is the
reluctance of the magnetic circuit?
A. 2.54 x 10-2 Gb/Mx
B. 6.44 x 10-3 Gb/Mx
C. 6.44 x 10-4 Gb/Mx
D. 2.54 x 10-3 Gb/Mx
- D. 2.54 x 10-3 Gb/Mx
- The torque exerted by an electric
field on a dipole is:
A. parallel to the field and
perpendicular to the dipole
moment
B. parallel to both the field and
dipole moment
C. perpendicular to both the field
and dipole moment
D. parallel to the dipole moment and
perpendicular to the field
- C. perpendicular to both the field
and dipole moment
- A certain laminated steel core has a
permeability of 3000. The length is 5
cm and the cross section is 2 sq. cm.
What is its reluctance?
A. 7500 C. 1200
B. 8.33 x 10-4
D. 2.5
- B. 8.33 x 10-4
- The force exerted by a uniform
electric field on a dipole is:
A. parallel to the dipole moment
B. perpendicular to the dipole
moment
C. perpendicular to the electric field
D. None of the above
- D. None of the above
47.If a current of 5A flows through a
long wire of radius 0.004 meter, what
is the flux density (H) produced 0.02
meter away from the surface of the
wire.
A. 19.70 AT/m
B. 39.80 AT/m
C. 66.34 AT/m
D. 33.17 AT/m
- D. 33.17 AT/m
- A charged particle is projected into a
region into a region of uniform
parallel, E and B fields. The force on
the particle is:
A. zero
B. at some angle < 90 with the field
lines
C. along the field lines
D. perpendicular to the field lines
- B. at some angle < 90 with the
field lines
- A magnetomotive force is supplied
by a current of one ampere through
100 turns. The magnetic circuit
consists of a steel core of 1000
permeability, 10 cm long and 4 sq.
cm area and an air gap one cm long.
What is the field intensity at the air
gap?
A. 12.25 Oe C. 497.66 Oe
B. 100.53 Oe D. 124.4 Oe
- D. 124.4 Oe
- An electric field exerts a torque on a
dipole only if:
A. the field is parallel to the dipole
moment
B. the field is not parallel to the
dipole moment
C. the field is perpendicular to the
dipole moment
D. the field is not perpendicular to
the dipole moment
- B. the field is not parallel to the
dipole moment
- Two point charges are the same
value, what is the value of each
charge in stat coulomb?
A. 8.90 stat coulomb
B. 9.90 stat coulomb
C. 6.90 stat coulomb
D. 7.90 stat coulomb
- B. 9.90 stat coulomb
- Three equal positive charges of 10
statcoulomb each are located at the
vertices of an equilateral triangle of 2
cm leg. What is the magnitude of the
force acting on each charge?
A. 12.5 dynes C. 25 dynes
B. 43.3 dynes D. 50 dynes
B. 43.3 dynes
- Two spheres separated from each
other by 10m have charges of 0.001
coulomb and 0.003 coulomb
respectively. In between the two
spheres is a point of zero electric
field. What is the distance from the
0.001 coulomb sphere?
A. 6.34 m C. 7.78 m
B. 2.24 m D. 3.66 m
D. 3.66 m
1
The electric field due to a uniform distribution of charge on a spherical shell is zero:
only inside the shell
2
An electron traveling north enters a region where the electric field is uniform and points north. The electron:
slow down
3
Calculate the magnitude of the electric field at a point that is 30 cm from a point charge Q = -3.2 x 10ˉ⁶ C.
3.0 x 10⁵ N/C
4
Two previously uncharged capacitors are connected in series and then charged with a 12 V source. One capacitor is 30 µF and the other is unknown. If the voltage across the first capacitor is 8 V, find the capacitance of the unknown capacitor.
60 µF
5
An electric field is most directly related to:
the force acting on a test charge
6
Three condensers of 6, 10 and 15 µF are connected in series across a 200 V supply. If the condensers are disconnected, how much energy can the charged condensers provide if connected across each other with like polarities together?
0.052 J
7
Choose the INCORRECT statement:
According to Gauss` law. if a closed surface encloses no charge, then the electric field must vanish everywhere on the surface
8
A 20 µF capacitor is charged by a 12-V battery. What is the stored energy in the capacitor?
1.44 x 10ˉ³ J
9
A 40 µF capacitor is charged to store 0.2 J of energy. An uncharged 60 µF capacitor is connected in parallel with the first one through a perfectly conducting leads. What is the energy lost due to the work done by the charges in spreading out over two capacitors?
0.12 J
10
A charged particle is placed is placed in an electric field that varies with location. No force is exerted on this charge:
at locations where the electric field is zero
11
Find the connection of capacitors 1 µF, 3 µF and 4 µF needed to have a total of 2 µF.
1 µF and 3 µF in parallel, series with 4 µF.
12
When the dipole moment of a dipole in a uniform electric field rotates to become more nearly aligned with the field:
the field doe positive work and the potential energy decreases
13
A charged point is particle is placed at the center of a spherical Gaussian surface. The electric flux ɸ E is changed if:
the point charge is moved to just outside the sphere
14
Three capacitors C₁ = 3 µF, C₂ = 6 µF and C₃ = 9 µF are connected in parallel. Find the equivalent capacitance in µF.
18
15
Two electrons in vacuum experience a force of 2 x 10ˉ¹⁵ N. How far apart are the electrons?
3.39 x 10ˉ⁷ m
16
Find the capacitance of a two-plate capacitor of plate area 12 in² dielectric constant of 6 and dielectric thickness of 0.01 in.
1.6 nF
17 A hollow conductor is positively charged. A small uncharged metal ball is lowered by a sild thread through a small opening in the top of the conductor and allowed to touch its inner surface. After the ball is removed, it will have:
no appreciable charge
19
Three equal positive charges of 10 statC each are located at the vertices of an equilateral triangle of 2 cm leg. What is the magnitude of the force acting on each charge?
43.3 dynes
20
Three capacitors having capacitances of 5, 10 and 12 µF are connected in parallel across 600 V mains. Determine the single capacitor in µF that can replace the combination.
27
21
Two-point particles, with charges of q₁ and q₂, are placed a distance r apart. The electric field is zero at a point P between the particles on the line segment connecting them. We conclude that:
q₁ and q₂ must have the same sign but may have different magnitudes
22
A capacitor whose plates is 20 cm x 3 cm and is separated by a 1.0-mm air gap is connected across a 12-V battery. Determine the charge accumulated on each plate after a long time.
6.4 x 10ˉ¹⁰ C
23
A particle with charge Q is placed outside a large neutral conducting sheet. At any point in the interior of the sheet the electric field produced by chares on the surface is directed:
toward Q
24
Two square parallel plates (0.04 m x 0.04 m) are separated by a 0.1 cm thick insulator with dielectric constant of 3.4. The plates are connected across 200 V. What is the charge on the plates?
9.63 x 10ˉ⁹ C
25
An electric field exerts a torque on a dipole only if:
the field is not parallel to the dipole moment
