Q: A converging lens with a focal length of $$f = 20\ \mathrm{cm} is $$used to form an image of an object placed $$60\ \mathrm{cm}$$ from the lens. What is the distance from the lens to the image?

$$30\ \mathrm{cm}$$ \\text{ on the opposite side of the lens from the object}$

Question 1

A converging lens with a focal length of $$f = 20\ \mathrm{cm} is $$used to form an image of an object placed $$60\ \mathrm{cm}$$ from the lens. What is the distance from the lens to the image?

Accepted Answer

$$30\ \mathrm{cm}$$ \text{ on the opposite side of the lens from the object}$

Question 2

Which of the following best describes the image formed by a concave mirror when the object is placed between the focal point and the mirror?

Accepted Answer

The image is virtual, upright, and larger than the object.

Question 3

A ray of light passes from air ($$n_1 = 1.00$) into glass (n_2$ = 1.50) at an $$angle of incidence of $$30^\circ. $$What is the angle of refraction inside the glass?

Accepted Answer

$$19.5^\circ$$

Question 4

Total internal reflection can only occur when:

Accepted Answer

Light travels from a medium with a higher refractive index to a lower refractive index.

Question 5

A parallel beam of light passes through a convex lens and converges at a point $$40\ \mathrm{cm}$$ from the lens. What is the focal length of the lens?

Accepted Answer

$$40\ \mathrm{cm}$$

Question 6

If the critical angle for a glass-air interface is $$42^\circ$$, what is the refractive index of the glass?

Accepted Answer

$$n = 1.50$$

Question 7

A diver underwater shines a flashlight upward at an angle of $$50^\circ to $$the normal. The critical angle for water-air is $$48.6^\circ. $$What happens to the light?

Accepted Answer

It is totally internally reflected back into the water.

Question 8

Which of the following statements about the focal point of a lens is correct?

Accepted Answer

The focal point is the point where rays parallel to the principal axis converge (or appear to diverge from) after passing through the lens.

Question 9

A real image is formed by a lens when:

Accepted Answer

The image can be projected onto a screen.

Question 10

A person looks at a coin at the bottom of a swimming pool. The coin appears to be closer to the surface than it actually is. This phenomenon is best explained by:

Accepted Answer

Refraction of light as it passes from water to air.

Question 11

A convex mirror always produces images that are:

Accepted Answer

Virtual and upright.

Question 12

A ray of light in glass ($$n = 1.5) $$strikes the glass-air interface at an angle of $$45^\circ. $$What is the angle of refraction in air?

Accepted Answer

$$73.7^\circ$$

Question 13

Which of the following best describes the path of a light ray passing through the center of a thin lens?

Accepted Answer

It passes straight through without deviation.

Question 14

A camera uses a converging lens to focus light onto film. If the lens is moved farther from the film, what must happen to the object distance to keep the image in focus?

Accepted Answer

The object must be moved closer to the lens.

Question 15

A student uses a lens to project an image of a distant building onto a screen. The distance from the lens to the screen is measured to be $$25\ \mathrm{cm}. $$What is the focal length of the lens?

Accepted Answer

$$25\ \mathrm{cm}$$

Question 16

Which of the following is a necessary condition for total internal reflection to occur?

Accepted Answer

The light must travel from a denser to a rarer medium.

Question 17

A ray of light passes from water ($$n = 1.33) $$into air ($$n = 1.00) at $$the critical angle. What is the angle of refraction in air?

Accepted Answer

$$90^\circ$$

Question 18

A lens forms an image that is the same size as the object and inverted. Where is the object located relative to the lens?

Accepted Answer

At twice the focal length from the lens.

Question 19

A person uses a concave mirror to apply makeup and sees an enlarged, upright image of their face. Where must their face be located relative to the mirror?

Accepted Answer

Between the focal point and the mirror.

Question 20

A ray of light is incident at $$60^\circ to $$the normal on a glass surface ($$n = 1.5). $$What is the critical angle for glass-air, and will total internal reflection occur?

Accepted Answer

Critical angle is $$41.8^\circ$$; total internal reflection will occur.

Optics: Reflection, Refraction, and Lenses

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