FREE National Opticianry Competency Questions and Answers

Question 1

You can change a lens' focal length by:

Accepted Answer

Changing the curvature of one surface

Answer

Curvature of one surface is altered. Because light waves are refracted at a greater angle with regard to the lens' optical axis, lenses with higher angles of curvature will have shorter focal lengths. The focal length of the lens shortens as the refractive index rises or gets more curved. The focal length won't change if the lens surface is coated, and increasing the diameter of the lens while maintaining the curvature of the surfaces has no effect on the angle of curvature or the way light waves are refracted.

Question 2

Types of "meniscus," "equiconcave," and "flat concave"

Accepted Answer

Minus lenses

Answer

Minus lenses cure for nearsightedness, often known as myopia, a condition in which a person can see things up close but not far away. The narrowest point of the lenses used to remedy this have a front surface that is flatter than their back surfaces and a center that is more curved. Meniscus lenses have two spherically curved surfaces that are concave on one side and convex on the other. A lens is referred to as equiconcave when both of its concave sides have the same focal length. On one side, flat concave lenses have a flat surface, and on the other, they have a spherical surface. Plus lenses come in the equiconvex, flat convex, and meniscus varieties.Meniscus lenses can be plus or minus, although concave describes minus lenses and convex describes plus lenses.

Question 3

What sort of lens has a surface that is both convex and concave?

Accepted Answer

Meniscus

Answer

One convex and one concave surface make up a meniscus lens. A positive meniscus lens is steeper on the convex side, making it thicker at the center and thinner on the edges, whereas a negative meniscus is thinner at the center than at the edges. Both myopic and hyperopic eyes can have their vision corrected with meniscus lenses. A biconvex lens has two convex surfaces, whereas a biconcave lens has two concave surfaces. One flat surface and one convex surface make up a plano-convex lens.

Question 4

A lens's power is indicated by the word "axis."

Accepted Answer

FALSE

Answer

The position of the astigmatism power, not its strength, is indicated by the lens's axis. The sphere represents the necessary lens power, and the cylinder represents the astigmatism correction power.

Question 5

What word best describes the direction change of light as it moves from one medium to another?

Accepted Answer

Refraction

Answer

Refraction describes how light slows down and bends as it transitions from air, a medium with a low density, into clear glass or plastic, a media with a high density. The light will bend toward the normal when it travels from air through a denser medium, such a lens, due to the difference in surface velocities between the two media. Diffusion is the term used to describe how light is dispersed when it passes through an uneven surface. When light bounces off a smooth surface, it is said to reflect; the light will reflect at the same angle as when it first reaches the surface. When white light is refracted, dispersion occurs, dividing it into the colors red, orange, yellow, green, blue, and violet.

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FREE National Opticianry Competency Questions and Answers