If he does not use the lenses, his near point will be 66.7 cm. For him to read a material at 50 cm, he has to use a lens of 2.0D.
<h3>What is the near point?</h3>
The near point is the nearest area which a person can see or have distinct vision. The focal length of the lens is f = 100/2.5 = 40cm
Then;
1/40 = -1/v + 1/25
1/v = 1/25 - 1/40
v = 66.7 cm
Also, for the purpose of reading at 50 cm
1/f = -1/50 + 1/25
1/f = 1/25 - 1/50
f = 50cm
The power of this lens is;
100/50 cm = 2 D
Learn more about lens: brainly.com/question/1503351
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<span>Buddy, remember one formula.. speed=distance/time
your all problems will be solved.
in this case the answer is 5 km per hr</span>
When a substance is heated, the molecules begin to vibrate faster and the space between molecules increases. So it would be speeding up.
The phenomenon which is responsible for this effect is called diffraction.
Diffraction is the ability of a wave to propagate when it meets an obstacle or a slit. When the wave encounters the obstacle or the slit, it 'bends' around it and it continues propagate beyond it. A classical example of this phenomenon is when a sound wave propagates through a wall where there is a small aperture (as in the example of this problem)
I believe the correct answer is A) From crest to crest.
~Silver