Light Flashcards
Light is propagated by means of …… waves
Transverse waves
Define a ray
It is a straight line drawn perpendicularly to the wavefronts with an arrow representing the direction in which lifht is travelling
Def a beam
Is a stream of light energy which is represented by a number of rays It may have parallel, diverging or converging rays
Def a transparent substance
It is one that transmits light and Through which objects can be clearly seen
Def translucent substance
Is one that transmits light but Through which objects cannot be clearly seen
Def opaque substance
One which does not transmit light
Name 2 kinds of reflection
Diffuse reflection
Regular reflection
Def Diffuse reflection
When the reflected light is scattered into various direction due to irregular structure of surface
Define Regular reflection
When the reflected light rays are even and in the same direction due to the reflective surface being smooth
Name the 2 laws of reflection
The angle of incidence is equal to the angle of reflection
The incident ray, normal and reflected ray all lie in the same plane
Name the 6 properties of an image in a plane mirror
Virtual
Erect
Laterally inverted
Same size than object
As far behind the mirror as the object is in front of the mirror
Cannot be projected onto a screen
Def a virtual image
It is an image which cannot be projected onto a screen because the rays of light do not pass through the image
Draw a periscope using mirrors
Draw a periscope using prisms
Draw a pinhole camera
Name the properties of a pinhole camera
Image is:
Smaller than the object
Real
Inverted Rays of light pass through the image
Def refraction
Is the bending of light when it passes obliquely from one medium to another of different optical density
Def an optical medium
It is a substance through which light can pass
Optical density refers to..
The refracting effect and not to the physical density of the substance
Define a Normal
It is a straight line drawn perpendicularly to the refracting surface at the point where light enters or leaves the medium
Give the two laws of Refraction
The incident and refracted rays are in the same plane as the normal to the surface at the point of incidence and lie on opposite sides of the normal
For a given colour of light, the ratio of the sine of the angle of incidence to the sine of the angle of refeaction is constant for any two given media
Name 4 facts referring to the path of a ray of light through a rectangular glass block
1) . A ray of light is refracted away from the normal when it enters an optically less dense medium obliquely
2) . A ray of light is reflected TOWARDS the normal when it enters an optically denser medium obliquely
3) . A ray of light is not refracted if it enters the medium at right angles
4) . The incidence and refracted ray leaving the block are parallell, but displaced laterally.
Name the two reasons why an image appear to be shallower in water than it really is
- Light is refracted AWAY from the normal when passing from water to air
- The brain imagines the ray of light to be travelling in a straight line
Draw a picture to describe the apparent bending of a pencil in water
Show the path of a ray of light through a triangular glass prism
Show 5 equations for calculating refractive index
- n= c/v
- n= sin i / sin r. From air into denser medium
- 1/n = sin i / sin r From dense to less dense
- n = 1/ sin c. c = critical angle
- n = real depth / apparent depth
Define the critical angle
It is the angle of incidence in the medium of greater optical density that results in an angle of refraction of 90o
List and explain the 2 conditions under which total internal reflection occurs
The ray of light must pass from a dense to a less dense optical medium The angle of incidence must exceed the critical angle of the optical medium
List some applications where total internal reflections occur
- Optic fibre cables
- Endoscopes
- Periscopes
- Binoculars
Def luminous source
Are objects which emit their own light
