Suppose a glass of water is sitting on the table in front of you. Since both the

Question

Suppose a glass of water is sitting on the table in front of you. Since both the glass and the water are transparent and colorless, how can you see them? All of these are good answers: pick the most basic and fundamental one. a. Light reflects off the outside of the glass and the top of the water b. Light refracts and distorts images of things behind or under the glass. c. The curved surface of the glass acts like a lens to magnify things behind or under it. d. Light travels slower in glass or water than in air A beam of light passing through glass approaches the surface of the glass at 70 degree as shown. Which letter marks the path which the light will take? a. A b. B c. C d. D This time, as a beam of light moves from air into glass, it makes a 45.0 degree angle of incidence. What angle of refraction will it form in the glass? a. 32.0 degree b. 30.0 degree c. 28.1 degree d. 22.8 degree In a physics lab you have a small light bulb 20.0 cm away from a converging lens that we will call lens number 1. You move a white index card screen back and forth until you see a sharp image of the bulb on the screen, and find that the screen is 20.0 cm behind the lens, or 40.0 cm from the bulb. a. 10.0 cm b. 13.3 cm c. 20.0 cm d. 40.0 cm In the next step of the lab, you hold a different lens, lens number 2, 16.0 cm from the bulb and find that the image is still in focus on the screen that is still 40.0 cm from the bulb. What would you say is the focal length of lens number 2? a. 8.0 cm b. 9.6 cm c. 12.0 cm d. 20.0 cm The images in the previous two questions are a. real for lens 1 and virtual for lens 2. b. virtual for lens 1 and real for lens 2. c. real for both lenses.

Explanation / Answer

26) (d) Light travels slower in glass or water than in air.

This is because light has different speed in different media and its speed decreses with the density of the medium. Because of this speed difference, we are able to see glass and water distinctly.

27) (a) A

C and D are not possible because they show the refracted rays going towards the normal, whereas when a ray moves from a denser(in this case glass) to rarer medium, it should move away from the normal.

So the possible rays are A or B.

Given the angle of incidence is 70 degrees which is greater than the critical angle for glass-air interface (which is around 48.6 degrees), So, total internal reflection takes place.

Hence the answer is A.

28) (c) 28.1 degrees

Using Snell's Law of refraction:

sin i/sin r = n2/n1

sin 45/sin r = 1.5/1

r = arcsin(0.4714)

r = 28.1 degrees

29) (a) 10.0 cm

Here object distance u = 20 cm

Image distance v = 20 cm

Using thin lens equation:

1/f = 1/u + 1/v

f = 10.0 cm

30) (b) 9.6 cm

Here

u = 16 cm

v = 40-16 = 24 cm

so:

1/f = 1/16 + 1/24

f = 9.6cm

31) (c) real for both lenses

Images formed on the other side of the lens are real

Hope this helps :)

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