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Phet explorations: color vision

Make a whole rainbow by mixing red, green, and blue light. Change the wavelength of a monochromatic beam or filter white light. View the light as a solid beam, or see the individual photons.

Color Vision

Section summary

  • Photon energy is responsible for many characteristics of EM radiation, being particularly noticeable at high frequencies.
  • Photons have both wave and particle characteristics.

Conceptual questions

Why are UV, x rays, and γ size 12{γ} {} rays called ionizing radiation?

How can treating food with ionizing radiation help keep it from spoiling? UV is not very penetrating. What else could be used?

Some television tubes are CRTs. They use an approximately 30-kV accelerating potential to send electrons to the screen, where the electrons stimulate phosphors to emit the light that forms the pictures we watch. Would you expect x rays also to be created?

Tanning salons use “safe” UV with a longer wavelength than some of the UV in sunlight. This “safe” UV has enough photon energy to trigger the tanning mechanism. Is it likely to be able to cause cell damage and induce cancer with prolonged exposure?

Your pupils dilate when visible light intensity is reduced. Does wearing sunglasses that lack UV blockers increase or decrease the UV hazard to your eyes? Explain.

One could feel heat transfer in the form of infrared radiation from a large nuclear bomb detonated in the atmosphere 75 km from you. However, none of the profusely emitted x rays or γ size 12{γ} {} rays reaches you. Explain.

Can a single microwave photon cause cell damage? Explain.

In an x-ray tube, the maximum photon energy is given by hf = qV . size 12{ ital "hf"= ital "qV"} {} Would it be technically more correct to say hf = qV + BE, size 12{ ital "hf"= ital "qV"+"BE"} {} where BE is the binding energy of electrons in the target anode? Why isn’t the energy stated the latter way?


What is the energy in joules and eV of a photon in a radio wave from an AM station that has a 1530-kHz broadcast frequency?

6.34 × 10 9 eV size 12{6 "." "34" times "10" rSup { size 8{ - 9} } " eV"} {} , 1.01 × 10 27 J size 12{6 "." "34" times "10" rSup { size 8{ - 9} } " eV"} {}

(a) Find the energy in joules and eV of photons in radio waves from an FM station that has a 90.0-MHz broadcast frequency. (b) What does this imply about the number of photons per second that the radio station must broadcast?

Calculate the frequency in hertz of a 1.00-MeV γ size 12{γ} {} -ray photon.

2 . 42 × 10 20 Hz size 12{2 "." "42" times "10" rSup { size 8{"20"} } " Hz"} {}

(a) What is the wavelength of a 1.00-eV photon? (b) Find its frequency in hertz. (c) Identify the type of EM radiation.

Do the unit conversions necessary to show that hc = 1240 eV nm, size 12{ ital "hc"="1240"" eV" cdot "nm"} {} as stated in the text.

hc = 6.62607 × 10 34 J s 2.99792 × 10 8 m/s 10 9 nm 1 m 1.00000 eV 1.60218 × 10 19 J = 1239.84 eV nm 1240 eV nm alignl { stack { size 12{ ital "hc"= left (6 "." "62607" times "10" rSup { size 8{ - "34"} } `J cdot s right ) left (2 "." "99792" times "10" rSup { size 8{8} } `"m/s" right ) left ( { {"10" rSup { size 8{9} } `"nm"} over {1`m} } right ) left ( { {1 "." "00000"`"eV"} over {1 "." "60218" times "10" rSup { size 8{ - "19"} } `J} } right )} {} #="1239" "." "84 eV" cdot "nm" {} # approx "1240 eV" cdot "nm" {}} } {}

Confirm the statement in the text that the range of photon energies for visible light is 1.63 to 3.26 eV, given that the range of visible wavelengths is 380 to 760 nm.

(a) Calculate the energy in eV of an IR photon of frequency 2.00 × 10 13 Hz. size 12{2 "." "00" times "10" rSup { size 8{"13"} } " Hz"} {} (b) How many of these photons would need to be absorbed simultaneously by a tightly bound molecule to break it apart? (c) What is the energy in eV of a γ size 12{γ} {} ray of frequency 3 . 00 × 10 20 Hz? size 12{3 "." "00" times "10" rSup { size 8{"20"} } " Hz"} {} (d) How many tightly bound molecules could a single such γ size 12{γ} {} ray break apart?

(a) 0.0829 eV

(b) 121

(c) 1.24 MeV

(d) 1 . 24 × 10 5 size 12{2 "." "24" times "10" rSup { size 8{5} } } {}

Prove that, to three-digit accuracy, h = 4 . 14 × 10 15 eV s, size 12{h=4 "." "14" times "10" rSup { size 8{ - "15"} } " eV" cdot s} {} as stated in the text.

(a) What is the maximum energy in eV of photons produced in a CRT using a 25.0-kV accelerating potential, such as a color TV? (b) What is their frequency?

(a) 25.0 × 10 3 eV size 12{" 25 " times " 10" rSup { size 8{3} } " eV"} {}

(b) 6 . 04 × 10 18 Hz size 12{" 6" "." "04 " times " 10" rSup { size 8{"18"} } " Hz"} {}

What is the accelerating voltage of an x-ray tube that produces x rays with a shortest wavelength of 0.0103 nm?

(a) What is the ratio of power outputs by two microwave ovens having frequencies of 950 and 2560 MHz, if they emit the same number of photons per second? (b) What is the ratio of photons per second if they have the same power output?

(a) 2.69

(b) 0.371

How many photons per second are emitted by the antenna of a microwave oven, if its power output is 1.00 kW at a frequency of 2560 MHz?

Some satellites use nuclear power. (a) If such a satellite emits a 1.00-W flux of γ size 12{γ} {} rays having an average energy of 0.500 MeV, how many are emitted per second? (b) These γ size 12{γ} {} rays affect other satellites. How far away must another satellite be to only receive one γ size 12{γ} {} ray per second per square meter?

(a) 1 . 25 × 10 13 photons/s size 12{" 1" "." "25 " times " 10" rSup { size 8{"13"} } " photons/s"} {}

(b) 997 km

(a) If the power output of a 650-kHz radio station is 50.0 kW, how many photons per second are produced? (b) If the radio waves are broadcast uniformly in all directions, find the number of photons per second per square meter at a distance of 100 km. Assume no reflection from the ground or absorption by the air.

How many x-ray photons per second are created by an x-ray tube that produces a flux of x rays having a power of 1.00 W? Assume the average energy per photon is 75.0 keV.

8.33 × 10 13 photons/s size 12{" 8" "." "33 " times " 10" rSup { size 8{"13"} } " photons/s"} {}

(a) How far away must you be from a 650-kHz radio station with power 50.0 kW for there to be only one photon per second per square meter? Assume no reflections or absorption, as if you were in deep outer space. (b) Discuss the implications for detecting intelligent life in other solar systems by detecting their radio broadcasts.

Assuming that 10.0% of a 100-W light bulb’s energy output is in the visible range (typical for incandescent bulbs) with an average wavelength of 580 nm, and that the photons spread out uniformly and are not absorbed by the atmosphere, how far away would you be if 500 photons per second enter the 3.00-mm diameter pupil of your eye? (This number easily stimulates the retina.)

181 km

Construct Your Own Problem

Consider a laser pen. Construct a problem in which you calculate the number of photons per second emitted by the pen. Among the things to be considered are the laser pen’s wavelength and power output. Your instructor may also wish for you to determine the minimum diffraction spreading in the beam and the number of photons per square centimeter the pen can project at some large distance. In this latter case, you will also need to consider the output size of the laser beam, the distance to the object being illuminated, and any absorption or scattering along the way.

Questions & Answers

how can chip be made from sand
Eke Reply
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Basic physics for medical imaging. OpenStax CNX. Feb 17, 2014 Download for free at http://legacy.cnx.org/content/col11630/1.1
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