# 9.11 Refraction  (Page 3/5)

 Page 3 / 5

The amount that a light ray changes its direction depends both on the incident angle and the amount that the speed changes. For a ray at a given incident angle, a large change in speed causes a large change in direction, and thus a large change in angle.

## Take-home experiment: a broken pencil

A classic observation of refraction occurs when a pencil is placed in a glass half filled with water. Do this and observe the shape of the pencil when you look at the pencil sideways, that is, through air, glass, water. Explain your observations. Draw ray diagrams for the situation.

## Section summary

• The changing of a light ray’s direction when it passes through variations in matter is called refraction.
• The speed of light in vacuum $c=2\text{.}\text{9972458}×{\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{m/s}\approx 3\text{.}\text{00}×{\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{m/s}.$
• Index of refraction $n=\frac{c}{v}$ , where $v$ is the speed of light in the material, $c$ is the speed of light in vacuum, and $n$ is the index of refraction.

## Conceptual questions

Diffusion by reflection from a rough surface is described in this chapter. Light can also be diffused by refraction. Describe how this occurs in a specific situation, such as light interacting with crushed ice.

Why is the index of refraction always greater than or equal to 1?

Does the fact that the light flash from lightning reaches you before its sound prove that the speed of light is extremely large or simply that it is greater than the speed of sound? Discuss how you could use this effect to get an estimate of the speed of light.

Will light change direction toward or away from the perpendicular when it goes from air to water? Water to glass? Glass to air?

Explain why an object in water always appears to be at a depth shallower than it actually is? Why do people sometimes sustain neck and spinal injuries when diving into unfamiliar ponds or waters?

Explain why a person’s legs appear very short when wading in a pool. Justify your explanation with a ray diagram showing the path of rays from the feet to the eye of an observer who is out of the water.

Why is the front surface of a thermometer curved as shown?

Suppose light were incident from air onto a material that had a negative index of refraction, say –1.3; where does the refracted light ray go?

## Problems&Exercises

What is the speed of light in water? In glycerine?

$2\text{.}\text{25}×{\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{m/s}$ in water

$2\text{.}\text{04}×{\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{m/s}$ in glycerine

What is the speed of light in air? In crown glass?

Calculate the index of refraction for a medium in which the speed of light is $2\text{.}\text{012}×{\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{m/s}$ , and identify the most likely substance based on [link] .

$1\text{.}\text{490}$ , polystyrene

In what substance in [link] is the speed of light $2\text{.}\text{290}×{\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{m/s}$ ?

There was a major collision of an asteroid with the Moon in medieval times. It was described by monks at Canterbury Cathedral in England as a red glow on and around the Moon. How long after the asteroid hit the Moon, which is $3\text{.}\text{84}×{\text{10}}^{5}\phantom{\rule{0.25em}{0ex}}\text{km}$ away, would the light first arrive on Earth?

$1\text{.}\text{28 s}$

Components of some computers communicate with each other through optical fibers having an index of refraction $n=1\text{.}\text{55}$ . What time in nanoseconds is required for a signal to travel 0.200 m through such a fiber?

$1.03 ns$

On the Moon’s surface, lunar astronauts placed a corner reflector, off which a laser beam is periodically reflected. The distance to the Moon is calculated from the round-trip time. What percent correction is needed to account for the delay in time due to the slowing of light in Earth’s atmosphere? Assume the distance to the Moon is precisely $3\text{.}\text{84}×{\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{m}$ , and Earth’s atmosphere (which varies in density with altitude) is equivalent to a layer 30.0 km thick with a constant index of refraction $n=1\text{.}\text{000293}$ .

Introduction about quantum dots in nanotechnology
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Bharti
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absolutely yes
Daniel
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it is a goid question and i want to know the answer as well
Maciej
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for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
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is Bucky paper clear?
CYNTHIA
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so some one know about replacing silicon atom with phosphorous in semiconductors device?
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Do you know which machine is used to that process?
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for screen printed electrodes ?
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What is lattice structure?
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or in general
Ebrahim
in general
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Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
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China
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types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
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many many of nanotubes
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what is the function of carbon nanotubes?
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I'm interested in nanotube
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