Refraction Chapter 4 Flashcards
What is refraction
the bending of a ray of light when it goes from one medium to another
What would be exception- when if there no refraction between two medium
when ray strikes the second medium at right angles
What is the angle of incidence
angle between incident ray and the normal
What is the angle of refraction
angle between the refracted ray and the normal
Does light refract towards or away from the normal
If travelling from a rarer to a denser medium refracts towards the normal.
If travelling from a denser medium to a rarer medium it travels away from the normal.
State the laws of refraction
the incident ray, the normal at the point of incidence and the refracted ray all lie in the same plane
the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
ie. sin i/sin r = n, where n is a constant
What is law 2 also known as
snell’s law
What is the refractive index
the ratio of sin i to the sin r when light travels from a vacuum or from air into that medium. symbol- n
What is the refractive index for any two media
xNy= 1/yNx
Where is apparent depth greatest
When viewed vertically above object, apparent depth decreases as you move to the side
How and when can you calculate the refractive index of a medium from real and apparent depth
When line of view of an object is perpendicular to the surface of the medium then:
N= Real depth / apparent depth
When is light fastest and at what speed
in a vacuum (or air difference is minuscule) at 3 x 10^8m/s
How is refractive index of a medium calculated using speed of light
xNy = Cx/ Cy
Ex: for air
airNx = speed of light in air/ speed of light in other medium
What is the relationship (effect) of refractive index on the speed of light in that medium
Greater the refractive index the slower the speed of light
Explain total internal reflection
when light going from a denser to a rarer medium strikes the second with an angle of incidence greater than the critical angle it does not enter the second medium. It is reflected back into the denser medium
What is the critical angle
When light travels from a denser to a rarer medium the angle of incidence whose corresponding angle of refraction is 90 degrees is called the critical angle (c) of those two media
What happens to light that strikes point of incidence at critical angle
it skims across the surface
Applying Snell’s law how can you find the refractive index of a medium from the critical angle. And use example of air
xNy = sinC
xNa = sinC and so aNx = 1/sin C
What is Snell’s window
If you are underwater looking up, light from outside can only enter water through circle of radius r - until critical angle - referred to as snell’s window
Where will ray that is shone onto one mirror which is located at right angles to two other mirrors travel back?
back in the direction the original ray came from
What are applications of snells window and total internal reflection
safety reflector of bike, reflective road signs
What is an optical fibre
A thin transparent rod (usually made of glass) which light can travel through by total internal reflection. They are solid and not hollow
Describe how light can escape an optical fibre
If light is bent at too large an angle, ray may strike at angle less than critical angle - therefore no internal reflection and light leaves fibre
If fibre comes into contact with another fibre total internal reflection will not occur as light will travel between fibres of same refractive index
How do you prevent light leaving an optical fibre because of same refractive index
coat optical fibre with a layer of glass of lower refractive index
Uses of optical fibres
telecommunications
dentists drill
Medical endoscope
In the experiment to verify snell’s law how is graph plotted
Sin of all values for i down one axis and sin of all values of r down other axis. Draw straight line through the origin
In the experiment to verify snell’s law how the refractive index found from the graph
fins the slope. must use formula y2-y1/x2-x1
Why is it more accurate to find the refractive index by graphing In the experiment to verify snell’s law
outliers can be identifies and there is reference to the origin
