Chapter 5 S1 Light Flashcards
:>>>>>>> refer to notes too!!!
What is light?
Light is a form of energy that enables us to see things around us when it enters our eyes
What are luminous objects? (+ examples)
Luminous objects are sources of light. We can see luminous objects because they produce light and enters our eyes directly (sun, stars, lamps, fire)
What are the 4 properties of light?
- it is a form of energy
- it is made up of seven different colours mixed uniformly to form white light
- it travels in straight line called rays; a bundle of light rays is called a beam
- it travels at a speed of 300 000 000m/s in a vacuum
What are non-luminous objects? (+ examples)
Non-luminous objects are not sources of light. We can see non-luminous objects because light from the lamp bounces/reflects off the object and enters our eyes (moon, desk, pen, book)
(FYI) What is a shadow?
A shadow is a dark area where light from a light source is blocked by an opaque object
What is reflection?
The bouncing of light off a mirror
What is the ray model of light used for?
To represent the path taken by the light rays as well as to understand how reflection takes place
What is the angle of incidence?
Angle between the incident ray and the normal
What is an incident ray?
Light ray hitting the reflecting surface
What is the normal?
Line perpendicular to the surface at the point of incidence
What is the angle of reflection?
Angle between the reflected ray and the normal
What is a reflected ray?
Light ray travelling away from the reflected surface
What is the 1st law of reflection?
Angle of incidence is equal to the angle of reflection
What are the 3 points to remember for regular reflection?
- parallel light rays incident on a smooth surface are reflected in one direction only
- Normals at all points of incidence are parallel
- clear images are formed
What is reflection on a smooth surface called?
Regular reflection
What is the 2nd law of reflection?
The incident ray, reflected ray and the normal, at the point of incidence, lie on the same plane
What is the refractive index?
n= c over v
c: speed of light in the vacuum
n: speed of light in medium
What are the characteristics of an image formed by convex mirror?
- virtual
- upright
- smaller
-used in blind spot mirrors or security mirrors
What is the reflection on a rough surface called?
Irregular reflection
What are the 3 points to remember for irregular reflection?
- Parallel light rays incident on a rough surface are reflected in different directions
- Normals at all points of incidence are not parallel
- images cannot be seen
What is the 2nd step of drawing a light diagram?
- Draw 2 rays from the image straight to the eye.
-Use dotted lines behind the mirror (virtual image)
-Use solid lines in front of the mirror surface
What is the 1st step to draw a ray diagram?
- Locate the position of the image by measuring the perpendicular distance of the object to the mirror.
-Object distance = Image distance
-Object size = Image size
What are the characteristics of an image formed by concave mirror?
- virtual
- upright
- magnified
-used in cosmetic mirrors, dentist mirrors or car headlights
What is the 3rd step for drawing a ray diagram?
At the point of incidence on the mirror, complete the ray diagram by drawing the incident rays from the object.
-indicate arrow!!!
What are the characteristics of real image?
- Formed by converging rays
- can be projected on a screen
- inverted
- images formed on screen using a projector or visualizer.
What is an effect of refraction?
The bending of light causes an object to appear nearer to the surface of the water.
Apparent depth < Real depth
What are the characteristics of an image formed by a plane mirror?
- image is upright
- image is same size as object
- object distance from mirror is equal to the image distance from mirror
- image is laterally inverted
- image formed is virtual
What are the characteristics of a virtual image?
- Formed by the extension of rays
- Cannot be projected on a screen
- Upright
- Images formed in a mirror, still water or any reflecting surface
What happens when the angle of incidence is zero?
The incident ray is now perpendicular to boundary surface and will travel without any deviation from its original path
What happens when a light ray travels from a medium that is more dense to less dense?
The speed of light increases and the light ray bends away from the normal
-eg: glass to air
-angle of incidence < angle of refraction
What happens when a light ray travels from a medium that is less dense to more dense?
The speed of light decreases and the light ray bends towards the normal
-eg: air to glass
-angle of incidence > angle of refraction
What is the definition of refraction?
Refraction refers to the change in direction of a light ray as it travels from one medium to another of a different optical density, due to a change in the speed of light in a medium
What is white light made up of?
It is a mixture of seven different colours called a spectrum.
What is the meaning of refractive index?
The ratio of speed of light in vacuum to the speed of light in the medium
How far away must the image be from the object for apparent depth questions?
One-third distance
What is dispersion of light?
The process where white light is split into its component colours
What happens when the incident beam of white light enters the prism?
It splits up and disperses into the spectrum
What are the order of colours in the spectrum of white light?
Red, Orange, Yellow, Green, Blue, Indigo & Violet (opposite if prism is upside down)
What happens to the light rays when they emerge from the prism?
They are again refracted by different amounts. A continuous spectrum of different colours overlapping the edges is seen
What is the term for when only a refraction of a single ray? (eg: refraction of a ray of red light)
Monochromatic - no dispersion
Which colour of the spectrum bends the most and least?
Red: bends least
Violet: bends most
What is the 3rd sentence that must be used to answer questions based on colour chart?
The components of light reflected by the object
What are the primary colours?
Red, Blue, Green
What is the 1st sentence that must be used to answer questions based on colour chart?
- ___ light consists of both ___ & ___ components
What is the 2nd sentence that must be used to answer questions based on colour chart?
The components of light absorbed by the object
What are the secondary colours?
- Yellow = Green + Red
- Magenta = Red + Blue
- Cyan = Blue + Green
