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The visible strip of the electromagnetic spectrum is highlighted and shown in the picture. The wave length range is from eight hundred nanometers on the left to three hundred nanometers on the right. The divisions between infrared, visible, and ultraviolet are not perfectly distinct. The colors in the visible strip are also not perfectly distinct; they are marked as bands labeled from red on the left to violet on the right.
A small part of the electromagnetic spectrum that includes its visible components. The divisions between infrared, visible, and ultraviolet are not perfectly distinct, nor are those between the seven rainbow colors.

Living things—plants and animals—have evolved to utilize and respond to parts of the electromagnetic spectrum they are embedded in. Visible light is the most predominant and we enjoy the beauty of nature through visible light. Plants are more selective. Photosynthesis makes use of parts of the visible spectrum to make sugars.

Integrated concept problem: correcting vision with lasers

During laser vision correction, a brief burst of 193-nm ultraviolet light is projected onto the cornea of a patient. It makes a spot 0.80 mm in diameter and evaporates a layer of cornea 0 . 30 μ m size 12{0 "." "30" mm} {} thick. Calculate the energy absorbed, assuming the corneal tissue has the same properties as water; it is initially at 34º C size 12{"34"°C} {} . Assume the evaporated tissue leaves at a temperature of 100º C size 12{"100"°C} {} .

Strategy

The energy from the laser light goes toward raising the temperature of the tissue and also toward evaporating it. Thus we have two amounts of heat to add together. Also, we need to find the mass of corneal tissue involved.

Solution

To figure out the heat required to raise the temperature of the tissue to 100º C size 12{"100"°C} {} , we can apply concepts of thermal energy. We know that

Q = mc Δ T , size 12{ ital "Q "= ital " mc"ΔT} {}

where Q is the heat required to raise the temperature, Δ T size 12{DT} {} is the desired change in temperature, m size 12{m} {} is the mass of tissue to be heated, and c size 12{c} {} is the specific heat of water equal to 4186 J/kg/K.

Without knowing the mass m at this point, we have

Q = m ( 4186 J/kg/K ) ( 100º C 34º C ) = m ( 276,276 J/kg ) = m ( 276 kJ/kg ). size 12{Q=m \( "4186 J/kg/K" \) \( "100"°C - "34"°C \) =m \( "276,276 J/kg" \) =m \( "276 kJ" \) } {}

The latent heat of vaporization of water is 2256 kJ/kg, so that the energy needed to evaporate mass m size 12{m} {} is

Q v = mL v = m ( 2256 kJ/kg ) . size 12{Q rSub { size 8{v} } = mL rSub { size 8{v} } = m \( "2256" \) " kJ"} {}

To find the mass m size 12{m} {} , we use the equation ρ = m / V size 12{ρ= {m} slash {V} } {} , where ρ size 12{ρ} {} is the density of the tissue and V size 12{V} {} is its volume. For this case,

m = ρ V = (1000 kg/m 3 ) ( area × thickness (m 3 )) = (1000 kg/ m 3 ) ( π ( 0.80 × 10 3 m ) 2 / 4 ) ( 0 . 30 × 10 6 m ) = 0.151 × 10 9 kg. alignl { stack { size 12{m = ρ"V "=" 1000 kg/m" rSup { size 8{3} } \( "area"´"thickness" \) } {} #="1000" \( p \( 0 "." "80"´"10" rSup { size 8{ +- 3} } " m" \) rSup { size 8{2} } /4 \) \( 0 "." "30"´"10" rSup { size 8{-6} } " m" \) {} # =0 "." "151"´"10" rSup { size 8{ +- 9} } " kg" "." {}} } {}

Therefore, the total energy absorbed by the tissue in the eye is the sum of Q size 12{Q} {} and Q v size 12{Q rSub { size 8{v} } } {} :

Q tot = m ( c Δ T + L v ) = ( 0.151 × 10 9 kg ) ( 276 kJ/kg + 2256 kJ/kg ) = 382 × 10 9 kJ . size 12{Q rSub { size 8{"tot"} } = m \( cD"T "+" L" rSub { size 8{v} } \) =0 "." "151"´"10" rSup { size 8{-9} } \( "276"+"2256" \) ="382"´"10" rSup { size 8{-9} } " kJ"} {}

Discussion

The lasers used for this eye surgery are excimer lasers, whose light is well absorbed by biological tissue. They evaporate rather than burn the tissue, and can be used for precision work. Most lasers used for this type of eye surgery have an average power rating of about one watt. For our example, if we assume that each laser burst from this pulsed laser lasts for 10 ns, and there are 400 bursts per second, then the average power is Q tot × 400 = 150 mW size 12{Q rSub { size 8{"tot"} } ´"400"="150"" mW"} {} .

Optics is the study of the behavior of visible light and other forms of electromagnetic waves. Optics falls into two distinct categories. When electromagnetic radiation, such as visible light, interacts with objects that are large compared with its wavelength, its motion can be represented by straight lines like rays. Ray optics is the study of such situations and includes lenses and mirrors.

When electromagnetic radiation interacts with objects about the same size as the wavelength or smaller, its wave nature becomes apparent. For example, observable detail is limited by the wavelength, and so visible light can never detect individual atoms, because they are so much smaller than its wavelength. Physical or wave optics is the study of such situations and includes all wave characteristics.

Questions & Answers

Why does earth exert only a tiny downward pull?
Mya Reply
hello
Islam
Why is light bright?
Abraham Reply
what is radioactive element
Attah Reply
an 8.0 capacitor is connected by to the terminals of 60Hz whoes rms voltage is 150v. a.find the capacity reactance and rms to the circuit
Aisha Reply
thanks so much. i undersooth well
Valdes Reply
what is physics
Nwafor Reply
is the study of matter in relation to energy
Kintu
a submersible pump is dropped a borehole and hits the level of water at the bottom of the borehole 5 seconds later.determine the level of water in the borehole
Obrian Reply
what is power?
aron Reply
power P = Work done per second W/ t. It means the more power, the stronger machine
Sphere
e.g. heart Uses 2 W per beat.
Rohit
A spherica, concave shaving mirror has a radius of curvature of 32 cm .what is the magnification of a persons face. when it is 12cm to the left of the vertex of the mirror
Alona Reply
did you solve?
Shii
1.75cm
Ridwan
my name is Abu m.konnek I am a student of a electrical engineer and I want you to help me
Abu
the magnification k = f/(f-d) with focus f = R/2 =16 cm; d =12 cm k = 16/4 =4
Sphere
what do we call velocity
Kings
A weather vane is some sort of directional arrow parallel to the ground that may rotate freely in a horizontal plane. A typical weather vane has a large cross-sectional area perpendicular to the direction the arrow is pointing, like a “One Way” street sign. The purpose of the weather vane is to indicate the direction of the wind. As wind blows pa
Kavita Reply
hi
Godfred
what about the wind vane
Godfred
If a prism is fully imersed in water then the ray of light will normally dispersed or their is any difference?
Anurag Reply
the same behavior thru the prism out or in water bud abbot
Ju
If this will experimented with a hollow(vaccum) prism in water then what will be result ?
Anurag
What was the previous far point of a patient who had laser correction that reduced the power of her eye by 7.00 D, producing a normal distant vision power of 50.0 D for her?
Jaydie Reply
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
Jaydie
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
Jaydie
A young woman with normal distant vision has a 10.0% ability to accommodate (that is, increase) the power of her eyes. What is the closest object she can see clearly?
Jaydie
29/20 ? maybes
Ju
In what ways does physics affect the society both positively or negatively
Princewill Reply
how can I read physics...am finding it difficult to understand...pls help
rerry Reply
try to read several books on phy don't just rely one. some authors explain better than other.
Ju
And don't forget to check out YouTube videos on the subject. Videos offer a different visual way to learn easier.
Ju
hope that helps
Ju
I have a exam on 12 february
David Reply
what is velocity
Jiti
the speed of something in a given direction.
Ju

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Source:  OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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