Light Flashcards
What is the relationship between refracted index, n, the angle of incidence and the angle of refraction (Snell’s law)?
n = sin(i) / sin(r)
What is the relationship between critical angle (c) and refractive index (n)?
Sin (c) = 1/n
What happens if a ray of light hits the centre (the normal) of a curved Perspex block and hits the straight side?
No change of direction because it hits the block at 90 degrees so the angle of incidence is 0 degrees
What happens if a ray hits the flat surface of the circular Perspex block at an angle of incidence of 20 degrees?
It’s reflected out the other side of the block
What is the critical angle?
Angle of incidence at a boundary with a less dense medium for which the angle of refraction is 90 degrees
What happens where the angle of incidence is greater than the critical angle?
The ray is reflected from the inside surface of the glass (this is total internal reflection)
Why does refractive index have no unit?
It is a ratio
Is the image from a periscope, upside down or the right way up when reflecting off 2 prisms?
Upside down, each time it hits the prism (mirror) it reflects 90 degrees. So as there are 2 prisms, it reflects a total of 180 degrees.
What are the 7 colours that are refracted in a light spectrum from least refractive onwards?
Red, orange, yellow, green, blue, indigo, violet
How are colours in the visible spectrum separated using a prism?
Dispersion
Why does dispersion occur?
As a result of refraction
If a colour in dispersion has a high frequency, what happens to the speed that light travels in the medium?
It slows down
If a colour in dispersion has a high frequency, what happens to the speed that light travels in the medium?
It slows down
What type of waves are light waves?
Transverse, they can be refracted and reflected
What is the law of reflection?
The angle of incidence is equal to the angle of reflection (i=r)
What is the difference between a wave entering a new medium when slowing down / speeding up?
Slowing down = bends towards the normal
Speeding up = bends away from normal
How does light enter an optical fibre?
At an angle that is greater than the critical angle
What is an optical fibre made of?
An inner core of glass, surrounded by a cladding of less dense glass
What happens when light hits the boundary between the core and cladding in an optical fibre?
Under goes total internal reflection
What pattern does light follow in an optical fibre?
Zigzag
What are optical fibres used for?
Communications (broadband, internet, or phone)
Endoscopes (medical purposes), Decorative lamps
What are advantages of optical fibres?
Cheap, lightweight, carry a large amount of information, can travel a long way without needing to be amplified
What happens if a ray is shone into a right-angle triangular prism?
It is reflected 90 degrees
