Midterm I Flashcards
Electric and magnetic fields are “in phase” which means that
they each are zero at the same points and reach their maxima at the same points in space
very far from the antenna the filed lines are quite flat over a reasonably large area and the waves are referred to as
plane waves
B and E are perpendicular to each other and to the direct of travel OR
direction of wave velocity
EM are – waves because the amplitude is perpendicular to the direction of wave travel
transverse
EM waves are always aves of – not of matter so they can propagate in empty space
fields
– electric charges gives rise to EM waves
accelerating
free space
no charges or conduction currents
speed of EM waves in empty space =
speed of light
The net magnetic flux through a closed surface is
zero
Gauss’s law for magnetism concludes that isolated magnetic poles
do not exist
An electric field is produced by a
changing magnetic field
A changing electric field will produce a
magnetic field
Electromagnetic waves are
transverse
Far from their source, EM waves are
plane waves
In the radiation field from an antenna, the E and B fields are – to one another
perpendicular
Right hand rule for the direction of propagation of the EM waves
point fingers of your right hand toward the E vector, curl your fingers towards the B vector, and the thumb will point the direction of propagation
If an EM wave has it magnetic field oscillating in the vertical direction, the direction of oscillation of the electric field is
horizontal
If the magnetic field in an EM wave is in the x-direction and the electric field in the wave is in the y-direction so the wave is traveling in the
negative z direction
An EM wave is propagating towards the west. At a certain moment the direction of the magnetic field vector points vertically up. What is the direction of the electric field vector?
(Horizontal or vertical, pointing south or down or north or up or east)
horizontal and south
An EM 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 direction
E vector is in the +z direction, the B vector is the the +x direction what is the direction of propagation of the EM wave?
+ y direction
Shortest wavelength: microwaves, IR, gamma rays, x-rays, UV
gamma rays
Order from low to high frequencies: radio waves, IR, Microwaves, UV, visible, x-rays, gamma rays
radio waves, microwaves, IR, visible, UV, x-rays, gamma rays
the energy per unit volume in an EM wave is – divided between E and B fields
equally
the force per unit area exerted by an EM wave is called
radiation pressure
– objects receives a larger amount of momentum
reflecting
an AM radio station indicates its location on the dial as 1030 –
kHz
Reflection, refraction, and the formation of images by mirrors and lenses has been successfully described by the
ray model of light
The angle of incidence must – the angle of reflection
equal
Describe the imaged formed by a plane mirror.
virtual and upright
plane mirrors produce images which are always –
the same size as the actual object
an image formed by a plane mirror is at a – the distance behind the mirror as the object is in front of the mirror
same
An image formed when the light rays do not actually pass through the image location and would not appear on paper or film placed at that location is called
virtual image
an image formed when the light rays pass through the image location and could appear on paper or film at that location is called
real image
Is it possible to see a virtual image?
Yes, the rays that appear to emanate from a virtual image can be focuses on the retina just like those from an illuminated object
A light ray is reflected by two mirrors that are perpendicular. The new direction of the ray is – from the original direction
180 degrees
How tall must a plane mirror be in order for you to be able to see your full image in it?
half your height
A concave mirror has a – focal length
positive
A convex mirror has a – focal length
negative
To find an image by ray tracing requires – rays
two
A beam of light that is parallel to the principal axis is incident on a concave mirror. What happens to the reflected beam of light?
It passes through the focal point of the mirror
A beam of light is parallel to the principal axis is incident on a convex mirror. What happens to the reflected beam of light?
It appears to be coming from the focal point on the other side of the mirror
A light ray, traveling obliquely to a concave mirror’s axis, crosses the axis at the mirror’s center of curvature before striking the mirror’s surface. After reflection, this ray passes through the mirror’s –
center of curvature
A light ray, traveling obliquely to a concave mirror’s surface, crosses the axis at the mirror’s focal point before striking the mirror’s surface. After reflection, this ray travels – to the mirror’s axis
parallel
If the image distance is positive, the image formed by a mirror is
real
If the image distance is negative, the image formed by a mirror is
virtual
If the absolute value of the magnification is larger than one, then the image is – than the object
larger
If the absolute value of the magnification is smaller than one, then the image is – than the object
smaller
when you stand in front of a concave mirror, exactly at its focal point
you won’t see your image because there is none
if you stand in front of a convex mirror, at the same distance from it as the radius of curvature
you will see your image and you will appear smaller
if you stand in front of a convex mirror at the same distance from it as its focal length
you will see your image and you will appear smaller
an object placed in front of a convex mirror at a distance larger than twice the focal length of the mirror will have an image that
is upright and reduced
concave spherical mirrors produce images which
could be smaller, larger, or the same size
convex spherical mirrors produce images which
are always smaller than the actual object
A single concave spherical mirror produces an image which is real only if the object distance is
greater than f
A single convex spherical mirror produces an image which is (V or R)
always virtual
If the magnification of a mirror is negative, then the image is
inverted and the mirror is concave
For all transparent materials, the index of refraction is – to 1
greater than
An index of refraction < 1 for a medium would imply that the speed of light in the medium is – than the speed of light in a vacuum
greater than
An index of refraction of diamond is 2.42. This means that a given frequency of light travels 2.42 times faster in –
vacuum than it does in diamond
When light enters a material of higher index of refraction, its speed
decreases
The angle of incidence is – the angle of refraction
may be >, <, or equal to
Light traveling at an angle into a denser medium is refracted – the normal
toward
Light enters air from water. The angle of refraction will be – the angle of incidence
greater than
A ray of light, which is traveling in air, is incident on a glass plate at a 45 degree angle. The angle of refraction in the glass is – than 45 degrees
less than
A beam of light in air is incident on a glass slab at an angle of incidence < 90 degrees. After entering the glass slab, the beam of light bends – to the normal drawn at the point of contact
towards
At a quiet pond with crystal clear water, you decide to fish with bow and arrow. When you aim at the fish you see, you must aim
deeper than you perceive the fish to be
The spreading of white light into its spectrum is called
dispersion
When light passes through a prism the color refracted most is
violet
Which color of light undergoes the smallest refraction when passing from air to glass?
red
When sill the critical angle exist?
n1 > n2
