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The wavelength of green light ranges between 500 nm an d 565 nm. Calculate the range of frequencies that correspond to this range of wavelengths.

  1. Use

    c = f × λ

    to determine f .

  2. c = f × λ f = c λ = 3 × 10 8 m · s - 1 565 × 10 - 9 m = 5 , 31 × 10 14 Hz
  3. c = f × λ f = c λ = 3 × 10 8 m · s - 1 500 × 10 - 9 m = 6 , 00 × 10 14 Hz
  4. The range of frequencies of green light is 5 , 31 × 10 14 Hz to 6 , 00 × 10 14 Hz .

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Calculating wavelengths and frequencies of light

  1. Calculate the frequency of light which has a wavelength of 400 nm. (Remember to use S.I. units)
  2. Calculate the wavelength of light which has a frequency of 550 × 10 12 Hz.
  3. What colour is light which has a wavelength of 470 × 10 - 9 m and what is its frequency?
  4. What is the wavelength of light with a frequency of 510 × 10 12 Hz and what is its color?

Dispersion of white light

White light, like the light which comes from the sun, is made up of all the visible wavelengths of light. In other words, white light is a combination of all the colours of visible light.

You learnt that the speed of light is different in different substances. The speed of light in different substances depends on the frequency of the light. For example, when white light travels through glass, light of the different frequencies is slowed down by different amounts. The lower the frequency, the less the speed is reduced which means that red light (lowest frequency) is slowed down less than violet light (highest frequency). We can see this when white light is incident on a glass prism.

Have a look at the picture below. When the white light hits the edge of the prism, the light which travels through the glass is refracted as it moves from the less dense medium (air) to the more dense medium (glass).

  • The red light which is slowed down the least , is refracted the least .
  • The violet light which is slowed down the most , is refracted the most .

When the light hits the other side of the prism it is again refracted but the angle of the prism edge allows the light to remain separated into its different colours. White light is therefore separated into its different colours by the prism and we say that the white light has been dispersed by the prism.

The dispersion effect is also responsible for why we see rainbows. When sunlight hits drops of water in the atmosphere, the white light is dispersed into its different colours by the water.

Addition and subtraction of light

Additive primary colours

The primary colours of light are red , green and blue . When all the primary colours are superposed (added together), white light is produced. Red, green and blue are therefore called the additive primary colours . All the other colours can be produced by different combinations of red, green and blue.

Subtractive primary colours

The subtractive primary colours are obtained by subtracting one of the three additive primary colours from white light. The subtractive primary colours are yellow , magenta and cyan . Magenta appears as a pinkish-purplish colour and cyan looks greenish-blue. You can see how the primary colours of light add up to the different subtractive colours in the illustration below.

Questions & Answers

The phenomenon that describes the change in the frequency
Neo Reply
Doppler effect
does the rate of reaction calculated by reactant equal to product
mudodzwa Reply
formula of heat reaction
Anelisiwe Reply
final energy-initial energy of substances
what is the difference between ethene and ethane
Joy Reply
Ethane is a saturated organic molecule while ethene is unsaturated Ethane has 2 carbon atoms and 6 hydrogen atoms, while ethene has 2 Carbons and 4 hydrogens Ethane has single bond between the 2 Carbon atoms while ethene has double bond
How do you know that the reaction is in acid medium or basic medium
Miss Reply
What formular is used when source and Observer are moving towards to each other
Esihle Reply
put a + on top n - on the bottom
what is doppler effect?
Ansiwe Reply
doppler effect is the perceived change in frequency of a sound caused by either the source or the listener
moving relative to each other
A Catalyst is a chemical substance that speeds up a chemical reaction.
Sheron Reply
It does this by lowering the activation energy.
what is exothermic
Nambile Reply
reaction that releases energy
what is a catalyst
Catalyst is to speed up the reaction
catalyst is a substance added into a solution to speed up the process
As it speeds up the reaction by lowering the activation energy, it does not take part in the reactants or products formed
reaction that release energy
what is exothermic
Nambile Reply
reaction that gives off heat to the surroundings
formula for calculating the heat of reaction
I need help in electrostatic
Muthuphei Reply
in exactly in electrostatic
send the question on electrostatic maybe I can help
factors affecting the rate of reaction
thabo Reply
I'm xiluva ...do we help those who are having challenges on their studies?
I mean on physical science
I believe it's supposed to be like that. Helping those who are having educational challenges
Yep physical sciences more specifically
ok ....nna I need some help in physics electricity ...just hints how we do what n how to solve some of the problem... just hints
The first thing you can do is to understand ohm's law and the difference between a series and parallel connection concerning current, resistance and potential difference
Hi Xiluva,not sure if this will be helpful but to understand electricity better I suggest you download Siyavula physical science books there's both a learner book and a teacher's guide I was struggling too they really did help you might be able to do some exercises after reading siyavula material
what diode mean
diode s a part of electrical current tht allows only moves to one direction ..only ...
allows current .....to flow to one direction I meant .
ok thanks
ok thanks guys
temperature surface area concentration addition of a catalyst
thank you mr
How to calculate e.p
zama Reply
What is polymer
Kwinda Reply
chemical compound with molecules bonded together in long ,repeating chains
hey guys i need help with the topic of forces and their application
Monica Reply
A force is a pull or push and it can be applied in rocket launchers moving cars & stoping (breaking them).
A force is that Agency which changes the object's state of rest or motion. A push or pull are the effects of force.

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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