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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

Calculate the work done by an 85.0-kg man who pushes a crate 4.00 m up along a ramp that makes an angle of 20.0º20.0º with the horizontal. (See [link] .) He exerts a force of 500 N on the crate parallel to the ramp and moves at a constant speed. Be certain to include the work he does on the crate an
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What is thermal heat all about
Abel Reply
why uniform circular motion is called a periodic motion?.
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when a train start from A & it returns at same station A . what is its acceleration?
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what is distance of A to B of the stations and what is the time taken to reach B from A
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the information provided is not enough
aliyu
Hmmmm maybe the question is logical
yusuf
where are the parameters for calculation
HENRY
there is enough information to calculate an AVERAGE acceleration
Kwok
mistake, there is enough information to calculate an average velocity
Kwok
~\
Abel
what is the unit of momentum
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wha are the types of radioactivity ?
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what are the types of radioactivity
Worku
what is static friction
Golu Reply
It is the opposite of kinetic friction
Mark
static fiction is friction between two surfaces in contact an none of sliding over on another, while Kinetic friction is friction between sliding surfaces in contact.
MINDERIUM
I don't get it,if it's static then there will be no friction.
author
It means that static friction is that friction that most be overcome before a body can move
kingsley
static friction is a force that keeps an object from moving, and it's the opposite of kinetic friction.
author
It is a force a body must overcome in order for the body to move.
Eboh
If a particle accelerator explodes what happens
Eboh
why we see the edge effect in case of the field lines of capacitor?
Arnab
what is wave
Muhammed Reply
what is force
Muhammed
force is something which is responsible for the object to change its position
MINDERIUM
more technically it is the product of mass of an object and Acceleration produced in it
MINDERIUM
wave is disturbance in any medium
iqra
energy is distributed in any medium through particles of medium.
iqra
If a particle accelerator explodes what happens
Eboh Reply
we have to first figure out .... wats a particle accelerator first
Teh
What is surface tension
Subi Reply
The resistive force of surface.
iqra
Who can tutor me on simple harmonic motion
yusuf Reply
on both a string and peldulum?
Anya
spring*
Anya
Yea
yusuf
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I dont have social media but i do have an email?
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Which is
yusuf
Where are you chatting from
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I don't understand the basics of this group
Jimmy
teach him SHM init
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Simple harmonic motion
yusuf
how.an.equipotential.line is two dimension and equipotential surface is three dimension ?
syed Reply
definition of mass of conversion
umezurike Reply
Force equals mass time acceleration. Weight is a force and it can replace force in the equation. The acceleration would be gravity, which is an acceleration. To change from weight to mass divide by gravity (9.8 m/s^2).
Marisa
how many subject is in physics
Adeshina Reply
the write question should be " How many Topics are in O- Level Physics, or other branches of physics.
effiom
how many topic are in physics
Praise
Praise what level are you
yusuf
If u are doing a levels in your first year you do AS topics therefore you do 5 big topic i.e particles radiation, waves and optics, mechanics,materials, electricity. After that you do A level topics like Specific Harmonic motion circular motion astrophysics depends really
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Yeah basics of physics prin8
yusuf
Heat nd Co for a level
yusuf
yh I need someone to explain something im tryna solve . I'll send the question if u down for it
Tamdy Reply
a ripple tank experiment a vibrating plane is used to generate wrinkles in the water .if the distance between two successive point is 3.5cm and the wave travel a distance of 31.5cm find the frequency of the vibration
Tamdy
hallow
Boniface
please send the answer
Boniface
the range of objects and phenomena studied in physics is
Bethel Reply
I don't know please give the answer
Boniface

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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