Multiple Choice Ch 31
Gauss's Law for magnetism tells us that the
net magnetic flux through a closed surface is zero
In the radiation field from an antenna, the electric and magnetic fields are
perpendicular to one another
far from their source, electromagnetic waves are
place waves
Using Maxwell's equations it can be shown that electromagnetic waves have a speed in free space of
(εOµO)-1/2.
An electromagnetic wave propagates along the +Y direction. If the E field at the origin is along the +z direction, what is the direction of the B field?
+X
For an xyz coordinate system shown in Fig. 31-2, if the E-vector is in the +z direction, and the B-vector is in the +x direction, what is the direction of propagation of the electromagnetic waves?
+Y
Which of the following statements are true?
Electromagnetic waves can exert pressure on an object. Electromagnetic waves transport energy from one region of space to another. Electromagnetic waves transport linear momentum.
AN electromagnetic wave is propagating towards the west. At a certain moment, the direction of the magnetic field vector associated with this wave points vertically up. What is the direction of the electric field vector?
Horizontal and pointing south
Which of the following are found within the electromagnetic spectrum?
X rays ultraviolet radiation microwave radiation visible light gamma rays
Which of the following statements are true regarding the electromagnetic spectrum?
Radio waves have wavelengths on the order of meters and very low photon energies. Infrared radiation has long wavelengths and low photon energies. Visible light lies at the center of the electromagnetic spectrum.
Which one of the following is the correct representation of the electromagnetic waves from longer to shorter wavelength?
Radio waves, microwaves, infrared, visible ,UV, X-rays, gamma rays
Which one of the following is the correct order of the electromagnetic spectrum from low to high frequencies?
Radio waves, microwaves, infrared, visible, UV, xRays, gamma rays
Suppose that an electromagnetic wave is traveling toward the east. At one instant at a given point, the electric field vector points upward. What is the direction of the magnetic field at this same given point and instant in time?
SOuth
Which one of the following is not an electromagnetic wave?
Sound waves
Consider an electromagnetic wave propagating through a region of empty space. How is the energy density of the wave partitioned between the electric and magnetic fields?
The energy density of an electromagnetic wave is equally divided between the magnetic and electric fields.
Consider the electromagnetic field produced at a given distance from a light source. Which of the following statements are true?
The intensity of the wave is proportional to the square of the fields. The intensity of the wave is proportional to the speed of light.
Two objects are in all respects identical except for the fact that one was coated with a substance that is an excellent reflector of light while the other was coated with a substance that is a perfect absorber of light. You place both objects at the same distance from a powerful light source so they both receive the same amount of energy U from the light. The linear momentum these objects will receive is such that:
The reflecting objects receives a larger amount of momentum.
What is the velocity of all electromagnetic waves in a vacuum?
The velocity of electromagnetic waves is nearly equal to 3 × 108 m/s.
In an electromagnetic wave the E and B fields are oriented such that
They are perpendicular to one another and perpendicular to the direction of wave propagation
An electric field is produced by a
changing magnetic field
The energy per unit volume in an EM wave is
equally divided between the electric and magnetic fields
Of the components of the electromagnetic spectrum listed below, which is associated with the shortest wavelengths?
gamma rays
Which of the following statements are true concerning electromagnetic radiation fields?
he electric field at any point is perpendicular to the direction of wave travel. The electric and magnetic fields are in phase with each other as they propagate through space. The magnetic field at any point is perpendicular to the direction of wave travel.
if an electromagnetic wave has its magnetic field oscillating in the vertical direction, the direction of the electric field is
horizontal
It can be concluded from Gauss's law for magnetism that
isolated magnetic poles do not exist.
An AM radio station indicates its location on the dial as "1030" what?
kHz
a changing electric field will produce a
magnetic field
If the magnetic field in an EM wave is in the x direction, the electric field in the wave is in the Y direction the wave is traveling in the negative Z direction
negative Z direction
the right hand rule for the direction of propagation of the electromagnetic wave is to
point the fingers of your right hand toward the E vector, curl your fingers towards the B vector, and thumb will point the direction of propagation
the force per unit area exerted by an electromagnetic wave is called the
radiation pressure
electromagnetic waves are
transvers
