# Colour and light  (Page 2/3)

 Page 2 / 3

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

$c=f×\lambda$

to determine $f$ .

2. $\begin{array}{ccc}\hfill c& =& f×\lambda \hfill \\ \hfill f& =& \frac{c}{\lambda }\hfill \\ & =& \frac{3×{10}^{8}\phantom{\rule{0.166667em}{0ex}}\mathrm{m}·{\mathrm{s}}^{-1}}{565×{10}^{-9}\phantom{\rule{0.166667em}{0ex}}\mathrm{m}}\hfill \\ & =& 5,31×{10}^{14}\phantom{\rule{0.277778em}{0ex}}\mathrm{Hz}\hfill \end{array}$
3. $\begin{array}{ccc}\hfill c& =& f×\lambda \hfill \\ \hfill f& =& \frac{c}{\lambda }\hfill \\ & =& \frac{3×{10}^{8}\phantom{\rule{0.166667em}{0ex}}\mathrm{m}·{\mathrm{s}}^{-1}}{500×{10}^{-9}\phantom{\rule{0.166667em}{0ex}}\mathrm{m}}\hfill \\ & =& 6,00×{10}^{14}\phantom{\rule{0.277778em}{0ex}}\mathrm{Hz}\hfill \end{array}$
4. The range of frequencies of green light is $5,31×{10}^{14}\phantom{\rule{0.277778em}{0ex}}\mathrm{Hz}$ to $6,00×{10}^{14}\phantom{\rule{0.277778em}{0ex}}\mathrm{Hz}$ .

## 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

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.

how does the earth revolute
What is the momentum
The product of the object's mass and it's velocity
Mvula
electric field def
FREENCO
how is ester formed
how is n ester formed
Aubrey
Alcohol reacts with a carboxylic acid
Texas
and the reaction is catalysed by sulphuric acid
Vhulenda
an athlete with a mass of 70kg runs at a velocity of 45km . determine the athlete's momentum
Is that a velocity or something else
msawenkosi
45km/h i guess
Texas
Change to m/s
Texas
45km/h = 12.5 m/s p=mv =70×12.5 =875 kg.m/s
Thato
what are the measures of the rates of reaction
Volume Concentration Temperature Pressure Surface Area
Thato
the principle of superposition of waves
what is work
is this a group chat
Hey can y'all define newton's 2nd law
mthebzification
If a resultant force act on an object...the object will accelerate in the direction of a resultant force,the acceleration of the object is directly proportional to the net force and inversely proportional to the mass of the object
mosa
how do you calculate tension force
Bulumko
use the formula Fnet=ma if there is tension connecting two objects
Sboniso
to calculate Tension, usually calculate acceleration first Draw separate free body diagrams for each body. Apply Fnet = ma to calculate Tension
Kevin
Hi people
Paul
how does temperature affect the equilibrium position
an increased temperature increases the average kinetic energy thus in turn increases the number of effective collisions........
Lwando
so...which reaction is favored between endothermic and exothermic .when temperature is increased..?
Blessing
exothermic reaction because energy is realised to the surroundings as heat and light energy ....graphical so much energy is realised as reactants to form product and because temperature is high rate of reaction is fast which means there is a successful collision
Code
INTEMENDO - INCREASE IN TEMPERATURE FAVOURS ENDOTHERMIC DETEMEXO - DECREASE IN TEMPERATURE FAVOURS EXOTHERMIC
Thato
an object will continue in a state of rest unless it is acted upon an unbalanced force
Newton's Law 1
Code
First Newton's Law
Azola
Newton's first law
Surprise
newton first law
Thinavhuyo
Newton's first law
Blessing
when pressure is increased what happen to volume
decreases
Code
care to explain?
Mpati
if pressure is applied to a pistol , the volume will decrease and particles will collide more frequently with the wall of a container .Each time they collide with the wall they exert a force on them .More collision means more force and the pressure will increase , that Boyle's Law
Code
Because the volume has decreased , the particle will collide more frequently with the wall of a container and each time they collide with the wall of a container they exert a force on them.More collision means more force so the pressure will increase , that Boyle's Law
Code
what is the difference between momentum and a change in momentum?
Change in momentum is the impulse of the object
Rachel
Momentum is a vector quantity equal to the product of the mass of the particle and its velocity
Mmola
How to name a branched molecule from right or left?
What's Free Fall
Free Fall means there is no acting force on that object.
Dingaletu
only gravitational force
Dingaletu
no external force acting on an object
Sphiwe
by only force of gravite
Sello
but gravitational force
Sphiwe
true
Lucky
a motion in which the only force acting is gravitational force
Blessing
and an object experiencing free fall is referred as a projectile
Blessing
Do polymers form restrictedly only if compound is saturated, only?