Light Flashcards
What is the speed of light?
3 x 108 m/s
What are the properties of a image from a plane mirror? (4)
- virtual
- same size
- laterally inverted
- same distance from mirror
What is an angle of incidence?
The angle between the incident ray and the normal
What is an angle of reflection?
The angle between the reflected ray and the normal
What is the relationship between angle of incidence and angle of reflection?
Both are equal in size
How does refraction from air to glass work?
Slows down and bends light towards the normal
How does refraction from glass to air work?
Speeds up and bends light away from the normal
How does refraction relate to change of speed?
The greater the refraction, the greater the change of speed
What is dispersion? (2)
- Separation of white light into a spectrum of colours.
- Due to the fact different colours of light travel at different speeds and take different paths
What are the colours of the colour spectrum?
Red
Orange
Yellow
Green
Blue
Indigo
Violet
What happens through light dispersion in a prism?
Red slows down the least so is refracted the least,
while violet slows down the most so is refracted the most
What are the types of lenses?
Convex (converging)
And
Concave (diverging)
What are the two pneumonics for mediums for refraction?
Less dense
Towards normal
More dense
More dense
Away from normal
Less dense
(In relation to the normal)
Where are the incident and reflected angles measured from?
The normal (and incident/reflected rays)
What are the two pneumonics for speed of waves after refraction?
Fast
Towards normal
Slow
Slow
Away from normal
Fast
in the equation V = fw (w should be lambda), what is the relationship between frequency and wavelength? (2)
- directly proportional, as one increases the other increases
- goes through the origin
Define Critical angle
The angle of incidence that results in a 90° angle of refraction
(not visible - along the semi circular glass block)
What is Total Internal Reflection (T.I.R)? (2)
- The complete reflection of light
- back into its original material
When does total internal reflection occur?
- When the angle of incidence is larger than the critical angle
- when moving from a more dense to less dense medium
What happens when a ray of light enters a medium at 90º?
There is no change in direction (unidirectional)
In a biconcave lens, where does light appear to come from?
The focal point
In a biconvex lens, where does light travel to?
Light converges at the focal point
What does SSDM stand for
Short
Sight
Diverging
Myopia
What does HLSC stand for
Hyperopia
Long
Sight
Converging
What does LXC stand for
Lens
Convex
Converging
What does LED stand for
Lens
ConcavE
Diverging
Why does short sight occur? (2)
- short sight usually occurs when the eyes grow slightly too long
- so that light doesn’t focus on the light-sensitive tissue (retina) at the back of the eye properly
What is the effect of short sight (2)
- the light rays focus just in front of the retina,
- resulting in distant objects appearing blurred
What form of lens is used to correct short sight?
A diverging (concave) lens
v
|
^.
What form of lens is used to correct long sight?
A converging (convex) lens
^.
|
V
Why does long sight occur? (3)
- long sight usually occurs when the eyeball is too short
- or the lens cannot be made thick enough
- to focus the light rays on the retina
What is the effect of long sight (2)
- the light rays would focus behind the retina
- so that nearby objects appear blurred
What are the properties of convex lenses? (3)
- Diminished
- Real image
- Inverted
What are the properties of concave lenses? (3)
- Erect
- Virtual image
- Diminished
What is the straight travel of light called?
The principal of linear wave propegation
What is the principal focus/focal point?
- The focus of a lens
- where light rays appear
- to converge or diverge from
What is a real image?
An image that can be projected onto a screen
What is a virtual image? (2)
- An image that appears to come from the object
- cannot be projected onto a screen
Where do you find the image from a concave (diverging) lens on a ray diagram?
Trace the rays on the left of the diagram
Where they meet is where the image comes from
Where do you find the image from a convex (converging) lens on a ray diagram?
Two lines from the top of an object:
- One through the origin
- One through the focal point after hitting the y axis
- where they meet is the image
Explain what happens when the angle of Incidence is:
- less than the critical angle
- equal to the critical angle
- more than the critical angle
- Refraction occurs, weak reflection
- 90º angle of refraction
- Total internal reflection - no refraction
After dispersion in a prism, what colour is top and what colour is bottom?
- Red on top (least refraction)
- Violet on bottom (most refraction)
Name an application of converging (convex) lenses
- Projectors
- Magnifying glasses
Name an application of diverging (concave) lenses
Telescopes
What are optic fibres?
How do they work?
- Lengths of solid glass core with an outer plastic sheath
- total internal reflection at the surface of the glass core
What are optic fibres used for in medicine?
Endoscopes - allow doctors to see inside a patient’s body
What are optical fibres used for? (2)
- endoscopes
- carrying video and telephone signals over long distances
What is the name of the centre point of a lens?
The optical centre
