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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

how vapour pressure of a liquid lost through convection
Yomzi Reply
Roofs are sometimes pushed off vertically during a tropical cyclone, and buildings sometimes explode outward when hit by a tornado. Use Bernoulli’s principle to explain these phenomena.
Aliraza Reply
Plz answer the question ☝️☝️
Aliraza
what's the basic si unit of acceleration
ELLOIN Reply
Explain why the change in velocity is different in the two frames, whereas the change in kinetic energy is the same in both.
Fabian Reply
Insulators (nonmetals) have a higher BE than metals, and it is more difficult for photons to eject electrons from insulators. Discuss how this relates to the free charges in metals that make them good conductors.
Muhammad Reply
Is the photoelectric effect a direct consequence of the wave character of EM radiation or of the particle character of EM radiation? Explain briefly.
Muhammad
Determine the total force and the absolute pressure on the bottom of a swimming pool 28.0m by 8.5m whose uniform depth is 1 .8m.
Henny Reply
how solve this problem?
Foday
P(pressure)=density ×depth×acceleration due to gravity Force =P×Area(28.0x8.5)
Fomukom
for the answer to complete, the units need specified why
muqaddas Reply
That's just how the AP grades. Otherwise, you could be talking about m/s when the answer requires m/s^2. They need to know what you are referring to.
Kyle
Suppose a speck of dust in an electrostatic precipitator has 1.0000×1012 protons in it and has a net charge of –5.00 nC (a very large charge for a small speck). How many electrons does it have?
Alexia Reply
how would I work this problem
Alexia
how can you have not an integer number of protons? If, on the other hand it supposed to be 1e12, then 1.6e-19C/proton • 1e12 protons=1.6e-7 C is the charge of the protons in the speck, so the difference between this and 5e-9C is made up by electrons
Igor
what is angular velocity
Obaapa Reply
angular velocity can be defined as the rate of change in radian over seconds.
Fidelis
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
physics can be defined as the natural science that deals with the study of motion through space,time along with its related concepts which are energy and force
Fidelis

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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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