What is the wavelength range of UVA?

320-400nm

What is the wavelength range of UVB?

280-320nm

What is a diverging pencil of light rays?

A set of light rays that emerges from a point source

What is a converging pencil of light rays?

A set of light rays focused at a point

What is the nature of light rays generated by an object at infinity?

An object at infinity produces a parallel pencil of light rays

Are light rays perpendicular or parallel to wavefronts?

perpendicular

What is vergence?

A measure of the curvature of a wavefront

What is the sign convention for the vergence of diverging light?

Negative

What is the sign convention for the vergence of converging light?

Positive

Is the magnitude of vergence smaller or larger as one approaches a light source or focal point?

larger

What are the units for vergence?

diopters = 1/meters

What is the vergence of a light source located infinitely far away?

0 (Zero). The curvature of the wavefront goes to 0 as the distance from the source goes to infinity.

What is considered the cutoff for being "infinitely far away" for clinical purposes?

20 ft (6m)

What is the refractive index of air?

1.00

What is the refractive index of water?

1.33

What is the refractive index of polycarbonate?

1.59

How does the speed of light change as it enters a more optically dense medium?

The speed of light slows

What is a refractive index?

The ratio of the speed of light in a vacuum to its speed in a given medium.

What is the phenomenon of refraction?

The deviation of a ray of light as light travels from one optical medium into another medium of different optical density. It is related to the change in the speed of light due to differing optical densities.

When a light ray travels into a material with a higher index of refraction, is it deviated toward or away from the surface normal?

Toward the surface normal

What is a "critical angle?"

The angle of incidence beyond which a light ray undergoes total internal reflection when entering one medium from another.

How can the critical angle be derived?

arcsin (n_2/n_1)

What is Snell's Law?

n_1 sin (theta_1) = n_2 sin (theta_2)

What is the secondary focal point of light traveling from one medium into another?

The point to which the light converges or from which the light appears to diverge as light enters the "secondary" medium from the primary medium.

What is the primary focal point of light traveling from one medium into another?

The point to which the light converges or from which the light appears to diverge as light enters the "primary" medium from the secondary medium.

What is the secondary focal length?

The distance from the surface apex to the secondary focal point

By what expression is the dioptric power (or refractive power) of a spherical surface given?

F = | n_2/f_2 |

Is the power of a converging optical system positive or negative?

Positive

What is a common sign convention for solving optical problems?

Light is assumed to travel from left to right. Distances to the right of a surface are positive, and those to the left are negative.

Does the primary focal length equal the secondary focal length of a spherical surface?

No. Power is "conserved," since F = | n_1/f_1 | = | n_2/f_2 |. That is, the spherical surface has the same power regardless of the direction of the light rays. This indicates that focal length scales with index of refraction.