Ch 13: Light and Geometrical Optics

Question 1

When a ray of light passing through one medium is reflected from the surface of another, the angle at which it bounces off the new medium is equal to the angle at which it strikes. In other words, the angle of ________ is equal to the angle of ________. This is known as the law of reflection.

Answer 1

reflection
incidence

p. 432

Question 2

The greater the value of n (the index of refraction) for a medium, the ______ light travels through that medium.

Answer 2

slower

p. 434

Question 3

When light parallel to the central axis of a concave mirror strikes the surface, it’s reflected through a point called the focus (or focal point), denoted by F. This point is halfway to the ______ of _________, C, of the mirror, which is the center of the sphere that the mirror is “cut from”.

Answer 3

center of curvature

p. 440

Question 4

Because the focal point (of a concave mirror) is halfway between the mirror and C, the distance from the mirror to the focal point, the focal length, f is equal to…

Answer 4

….half the radius of curvature.

• f =* ½r
  p. 440

Question 5

When using the mirror/thin lens equation, we write the focal length of a concave mirror is a ________ number, and we write the focal length of a convex mirror as a ________ number.

Answer 5

positive

negative

p. 443

Question 6

Myopia (nearsightedness) is a condition of the eye where the lens focuses the light rays to a position between the lens and the retina. To correct for this condition, a thin lens is placed in front of the eye that will help to focus light on the retina. The type of lens required is:

Answer 6

a diverging lens

[Free Practice AAMC exam, Q 43]

Question 7

The _____ of a lens is defined to be the reciprocal of f, the focal length. When f is expressed in meters, the unit of lens power is called the diopter (D).

Answer 7

power

p. 448

Question 8

The power of a combination lens is equal to the ____ of the ______ of the individual lenses.

Answer 8

sum

powers

p. 448

Question 9

Hyperopia (aka hypermetropia) is the technical name for ____________.

Answer 9

farsightedness

p. 449

Question 10

When the ciliary muscles of the eye squeeze the lens of the eye, increasing its curvature, this decreases its _____ ______.

Answer 10

focal length

p. 449

Question 11

What is the term for the decreasing ability of the eyes to accommodate?

Answer 11

presbyopia

p. 449

Question 12

Notice that diverging lenses have ________ focal lengths AND powers, while converging lenses have the opposite.

Answer 12

negative

p. 450

Question 13

Total internal reflection occurs when a light ray traveling in a medium of high refractive index approaches a medium of _____ refractive index. If the ray’s angle of incidence exceeds a certain critical angle, the light ray will undergo total internal reflection: All of the incident ray’s energy will be reflected back into its original medium; there will be no refracted ray.

What is the formula to calculate this critical angle?

Answer 13

lower

sin θ_crit = n₂ / n₁

p. 435

Question 14

A person, whose eye has a lens-to-retina distance of 2.0 cm, can only clearly see objects that are closer than 1.0 m away. What is the strength S of the person’s eye lens? (Note: Use the thin lens formula ​ ​.)

A.) –50 D

B.) –10 D

C.) 51 D

D.) 55 D

Answer 14

C. According to the thin lens formula, the strength of the eye lens is equal to the inverse of the focal length of the eye lens. Its numerical value is given by (1 m)⁻¹ + (0.02 m)⁻¹ = 1 D + 50 D = 51

[From AAMC Practice Exam 1, q 11]

Question 15

Knowing that the speed of light in the vitreous humor is 2.1 × 10⁸ m/s, what is the index of refraction of the vitreous humor? (Note: The speed of light in a vacuum is 3.0 × 10⁸ m/s.)

A.) 0.7

B.) 1.4

C.) 2.1

D.) 3.0

Answer 15

B. The index of refraction of a medium is equal to the ratio of the speed of light in vacuum to the speed of light in the medium, thus in this case is equal to (3.0 × 10⁸ m/s) / (2.1 × 10⁸ m/s) = 1.4.

Question 16

The energy of electromagnetic radiation is directly proportional to the number of photons, and the intensity of electromagnetic radiation is defined as energy emitted per unit time. Thus, intensity is directly proportional to the number of photons emitted. The energy of electromagnetic radiation is directly proportional to the number of photons, and the intensity of electromagnetic radiation is defined as energy emitted per unit time. Thus, intensity is directly proportional to the ______ of _______ emitted.

Answer 16

number

photons

[Practice Exam 1, Q 16]