Light Flashcards
What are the laws of reflection?
- The angle of incidence equals the angles of reflection
- The incident ray, reflected ray and normal all lie in the same plane
What are the five properties of a image formed by a plane mirror?
- Same size
- Upright
- Virtual
- Laterally inverted
- Same distance behind the mirror as the object in front
What is a real image?
An image which can be projected onto a screen
What is a virtual image?
An image which cannot be projected onto a screen
Diagram of reflection on a plane mirror?
Look in Book
Diagram of reflection on a periscope?
Look in Book
Diagram of reflection of light for image formation?
Look in Book
What is refraction?
The bending of light due to its change in speed after moving from one medium to another with a different refractive index.
What are the requirements for refraction?
1 – Ray passes from one medium into another with a different refractive index.
2 – At an angle of incidence > 0 degrees.
What are examples of refraction?
- Glasses
- Eyes
- Telescope
- Magnifying Glass
Does all light pass through when it is refracted?
When light passes from one medium, say air, to another, say glass, part is reflected back into the first medium ( 4% ) and the rest passes into the second medium with its direction changed.
Diagram of refraction through a water drop?
Look in Book
Diagram of refraction through a glass block?
Look in Book
What changes in the light when it enters the glass from air?
Speed - Decreases
Wavelength - Decreases
Frequency - Constant
What changes in the light when it exits glass into air?
Speed - Increases
Wavelength - Increases
Frequency - Constant
Why does certain colours of light refract less or more?
The amount of refraction that takes place depends on the change of speed in light.
Violet light refracts more as it experiences a greater change of speed than red light
What is dispersion?
When white light passes through an new medium the different colours of light are refracted by different amounts.
Red light slows down the least and refracts the least
Violet light slows down the most and refracts the most
What is the critical angle?
The critical angle is the (limiting) angle of incidence which gives an angle of reflection of 90 degrees
What two conditions are necessary for total internal reflection?
- The angle of incidence is greater than the critical angle
- The ray must be incident from a higher refractive index medium to a lower refractive index medium
How does total internal reflection take place when the angle of incidence is less than the critical angle
Refracts as normal with 4% reflecting internally
How does total internal reflection take place when the angle of incidence is equal to the critical angle
Refracts at a 90 degree angle with 4% reflecting internally
How does total internal reflection take place when the angle of incidence is greater than the critical angle
Does not refract and reflects 100% internally
Explain how optical fibre cables satisfy TIR?
Their core has a very high refractive index and the cladding that surrounds their core has a very low refractive index. Meaning as long as I > C, TIR takes place
What are non-medical uses of optical fibre?
Long distance communication as they allow transfer of large quantities of data along the cable at high speeds over large distances.
Bomb Disposal
FBI - Surveillance
Borescope - Used by engineers to inspect aircraft engines, gas turbines, steam turbines and diesel engines etc
