In searching the bottom of a pool at night, a watchman shines a narrow beam of l

Question

In searching the bottom of a pool at night, a watchman shines a narrow beam of light from his flashlight, 1.3mabove the water level, onto the surface of the water at a point d = 2.5 m from his foot at the edge of the pool(Figure 1) .

Part A

Where does the spot of light hit the bottom of the h = 2.1-m-deep pool? Measure from the bottom of the wall beneath his foot.

Express your answer to two significant figures and include the appropriate units.

A certain lens focuses light from an object1.75 m away as an image 41.8 cm on the other side of the lens.

Part A

What type of lens is it?

What type of lens is it?

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Part B

What is its focal length? Follow the sign conventions.

Express your answer to three significant figures and include the appropriate units.

0.62cm

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Part C

Is the image real or virtual?

Is the image real or virtual?

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Explanation / Answer

PART A)

We find the angle of incidence from the distances tan 1 = d1 /h1 = 2.5m /1.3m = 1.9231, 1 = 62.53 .

For the refraction from air into water:

we have nair sin 1 = nwater sin 2,

sin 2 = 1.00/ 1.33 sin 62.53 2 = 41.84 We find the horizontal distance from the edge of the pool from l = d1 + d2 = d1 + h2 tan 2 = 2.5m + 2.1m tan 41.84 = 4.4m

Focal length , f = Oi/O+i = 1.75*(-0.418)/1.75-0.418 = - 0.549 m = Negative f

=> Concave lens

=> Diverging lens

PART B)

f = - 0.549 m

PART C)

Image is Real & Inverted

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