Unit 4 concepts 3

Question 1

What were Maxwell’s and Hertz’s contributions to electromagnetic waves?

Answer 1

Maxwell predicted theoretically on the basis of the laws of electricity and magnetism that
electromagnetic waves should exist. Hertz first demonstrated experimentally the existence of electromagnetic waves.

Question 2

What is an electromagnetic wave?

Answer 2

An electromagnetic wave is a particular combination of time‐varying electric and magnetic fields that propagate through space at the speed of light.

Question 3

What are the relative orientations of the electric and magnetic fields of an electromagnetic wave?

Answer 3

In an electromagnetic wave, the electric and magnetic fields are perpendicular to each other and to the direction of propagation of the wave.

Question 4

What is the relation between the wavelength and frequency of an electromagnetic wave?

Answer 4

Lambda(frequency)=c

Question 5

What is a typical wavelength and frequency of a microwave?

Answer 5

Microwaves have typical wavelengths of approximately centimeters. The corresponding
frequency of a 1 cm microwave = (3x108 m/s) / 0.01 m = 3x1010 Hz.

Question 6

The frequency of an AM radio station is 850 kHz. Why is it possible to pick up this station anywhere between 845 and 855 kHz?

Answer 6

Broadcast transmitters produce electromagnetic waves over a certain bandwidth or range
of frequencies.

Question 7

Why are microwavable means not packaged in aluminum containers?

Answer 7

Microwaves do not penetrate through conductors but are reflected from them. The
aluminum container will prevent the microwaves from penetrating through and cooking the food.

Question 8

What is the index of refraction?

Answer 8

The index of refraction n is the ratio of the speed of light in vacuum to the speed of light in a medium: n = c/v.

Question 9

(a) What is the range of wavelengths of visible light?

(b) Where do UV wavelengths lie
relative to visible light?

(c) Where do the IR wavelengths lie relative to visible light?

Answer 9

(a) the wavelengths of visible light range from approximately 400 nm to 700 nm.

(b) UV
wavelengths smaller than 400 nm, and

(c) IR wavelengths are longer than 700 nm.

Question 10

What is the phenomenon of refraction and how is it characterized by the index of
refraction?

Answer 10

Refraction is the bending of a light ray as it enters the boundary between two materials. The amount of bending depends on the indices of refraction of the two media.

Question 11

(a) How is a ray of light bent when it goes from air into glass?

(b) How is a ray of light bent
when it goes from water into air?

Answer 11

(a) A ray propagating from air into glass is bent toward the normal.

(b) A ray going from
water into air is bent away from the normal. The normal is the imaginary line that is
perpendicular to the boundary surface.

Question 12

What is total internal reflection? What is a practical application of this phenomenon?

Answer 12

Total internal reflection is an optical phenomenon that occurs when a light ray starting in a medium of index of refraction n1 is reflected at the boundary of another medium with index of refraction n2 < n1. This only occurs if the angle of incidence is greater than some critical value that depends on the materials. Fiber optics communications is based on this phenomenon.

Question 13

1. What is the phenomenon of dispersion?

Answer 13

Dispersion is the name for the fact that the index of refraction of a material depends on the wavelength of light. Dispersion is observed when a beam of white light enters a prism and emerges as multiple beams of different colors. It is also the phenomenon that causes the formation of rainbows due to the dispersion of sunlight from water droplets in the
atmosphere.

Question 14

What phenomenon is the cause of blue skies and red sunsets?

Answer 14

Blue skies and red sunsets are the result of the scattering of sunlight from air molecules. The scattering depends strongly on wavelength.

Question 15

What is the law of reflection?

Answer 15

The angle of reflection = the angle of incidence

Question 16

Describe the characteristics of the image formed by a plane mirror.

Answer 16

A plane mirror produces a virtual image that is upright, the same size as the object, and located the same distance behind the mirror as the object is in front of the mirror.

Question 17

How tall must a plane mirror be so that a person can see from his head to his toe?

Answer 17

A person can see her entire self with a plane mirror that is half as tall as she is.

Question 18

How are parallel light rays reflected by a concave mirror?

Answer 18

A concave mirror reflects parallel rays to a single focus point.

Question 19

How are parallel light rays reflected by a convex mirror?

Answer 19

A convex mirror causes parallel rays to diverge after reflection.

Question 20

What is a real image and a virtual image?

Answer 20

In a real image, light rays actually converge at the image location. In a virtual image, light rays diverge when they leave the object and appear to come from a point where no light rays actually are.

Question 21

What type of mirror is used to produce a magnified image of an object?

Answer 21

A concave mirror can be used to give a magnified image.

Question 22

What type of mirror is used to provide a wide angle view?

Answer 22

A convex mirror is used to provide a wide angle view.

Question 23

What principle of optics explains how lenses work?

Answer 23

The law of refraction

Question 24

What is the effect of a converging lens on parallel light rays?

Answer 24

A converging lens causes parallel light rays to converge to a focus point.

Question 25

What is the effect of a diverging lens on parallel light rays?

Answer 25

A diverging lens cause parallel light rays to diverge from a focal point.

Question 26

What type of image is formed of an object located far from a converging lens?

Answer 26

For an object located well beyond the focal point of a converging lens, the image is real, and inverted.

Question 27

How can a converging lens be used as a magnifying lens?

Answer 27

A converging lens can be used to produce an enlarged image if the object is placed within the focal length of the lens.

Question 28

How is the human eye capable of focusing on both near and far objects?

Answer 28

The lens in the human eye is flexible so that its focal length can be changed.

Question 29

What type of corrective lens is used for nearsightedness?

Answer 29

A diverging lens is used to correct nearsightedness.

Question 30

What type of corrective lens is used for farsightedness?

Answer 30

A converging lens is used to correct farsightedness.

Question 31

What is the cause of astigmatism?

Answer 31

Astigmatism is due to an irregularity in the curvature of the cornea or lens of the eye.

Question 32

What is physical optics?

Answer 32

Physical optics is the branch of optics that deals with effects due to the wave nature of light.

Question 33

What is the diffraction of light?

Answer 33

Diffraction is the spreading out of light waves after passing through a small opening.

Question 34

How is the polarization of an electromagnetic wave defined?

Answer 34

The polarization of an electromagnetic wave is defined as the direction in which the electric field oscillates.

Question 35

What is the difference between polarized and unpolarized light?

Answer 35

In polarized light the electric field vibrates in only one direction whereas in unpolarized light the electric field is oriented randomly in all directions around the direction of propagation.

Question 36

What if the effect of placing a Polaroid sheet in the path of unpolarized light?

Answer 36

Unpolarized light passing through a Polaroid sheet will be polarized in the direction of the axis of the Polaroid sheet

Question 37

What if the effect of placing a Polaroid sheet in the path of polarized light?

Answer 37

The effect of a Polaroid sheet on polarized light depends on the angle between the direction of polarization of the light and the axis of the Polaroid sheet. If the direction of polarization
is parallel to the axis of the Polaroid sheet, the light passes through with no change. If the
direction of polarization is perpendicular to the axis of the Polaroid sheet, the light does not
pass through.

Question 38

What are constructive and destructive interference?

Answer 38

Constructive interference occurs when two wave that are in phase are added together. The intensity of the combined wave is the sum of the intensities of the individual waves. Destructive interference occurs when two waves that are not in phase are added together. If the waves are exactly out of phase, the waves cancel out each other.

Question 39

A laser beam passes through a narrow circular aperture. What pattern is observed on a screen downstream of the aperture?

Answer 39

When a laser beam passes through a small circular aperture, diffraction produces a series of
concentric rings on the screen.

Question 40

What types of waves are subject to the phenomenon of diffraction?

Answer 40

Diffraction is a phenomenon that occurs with all types of waves.

Question 41

How does diffraction affect our ability to distinguish closely spaced objects?

Answer 41

Diffraction causes the light entering our eyes to spread out and if the diffraction patterns from 2 objects overlap, they appear as one object.

Question 42

What is thin film interference?

Answer 42

If a thin film is on a surface, there is interference between light reflected from the film and the light reflected by the surface under the film. Since different wavelengths of light are refracted by different amounts, white light is spread out in colors.

Question 43

Why does the surface of a DVD look colorful in white light?

Answer 43

The surface of a DVD has many narrowly spaced features that act as a diffraction grating
which causes white light to be spread out by color.