LIGHT - GR9 by Lizelle Swanepoel

NOTES ON LIGHT - EXAMINED IN FULL IN JUNE EXAMS

lizellexs — 2021-07-20 11:25:20 UTC

The nature of light

lizellexs — 2021-07-20 11:26:11 UTC

An object can be seen when the light that is reflected or emitted by an object enters the eye.
If no light enters the eye, the absence of light is interpreted as darkness and the object appears to be black.
Light travels in straight lines (unless acted upon by a surface or force).

Rule 2 - REFLECTION (REGULAR VS DIFFUSE)

lizellexs — 2021-07-20 11:34:31 UTC

NATURE OF LIGHT: rule 1

lizellexs — 2021-07-20 11:40:58 UTC

UMBRA VS PENUMBRA

lizellexs — 2021-07-20 11:46:53 UTC

Pinhole camera

lizellexs — 2021-07-20 11:47:47 UTC

A simple pinhole camera can be made out of a shoe box painted black inside. Cut square holes out of each end of the box. Fix a sheet of aluminium foil over one hole and make a small, round hole (aperture) in the foil with a pin. Paste a piece of tracing paper over the other hole to serve as a screen. Aim the aperture at an object and observe the image produced on the tracing paper.

PINHOLE CAMERA

lizellexs — 2021-07-20 11:49:13 UTC

What characteristic of light explains why an inverted image of an object forms in a pinhole camera?

2 TYPES OF REFLECTION: REGULAR VS DIFFUSE

lizellexs — 2021-07-20 21:24:05 UTC

SPECULAR (REGULAR) VS DIFFUSE

KNOW:

Laws of reflection

The angle of incidence is equal to the angle of reflection.
The incident ray, normal and reflected ray, at the point of incidence (B) all lie in the same plane.

Transmission, absorption and reflection

lizellexs — 2021-07-20 21:24:29 UTC

Light falling on an object can be transmitted (pass through), absorbed and/or reflected.

ABSORPTION VS REFLECTION OF LIGHT

lizellexs — 2021-07-20 21:29:19 UTC

Many objects contain atoms capable of either selectively absorbing, reflecting or transmitting one or more frequencies of light.
The frequencies of light that become transmitted or reflected to our eyes will contribute to the color that we perceive.

SUBTRACTIVE MIXING OF LIGHT

lizellexs — 2021-07-20 21:31:47 UTC

7 colours (ROYGBIV) of light fall onto any object, it absorbs 6 colours that is not its own and reflects the colour of light similar to its own colour.
Key: ROYGBIV = Red, Orange, Yellow, Green, Blue, Indigo, Violet

Plants are green (G):

They absorb ROYBIV
They reflect G

lizellexs — 2021-07-20 21:33:44 UTC

ABSORPTION, REFLECTION & TRANSMISSION OF LIGHT

lizellexs — 2021-07-20 21:48:00 UTC

Properties of a plane (flat) mirror image

lizellexs — 2021-07-20 21:55:06 UTC

1. Laterally inverted.
2. Upright.
3. Same size as object.
4. As far behind the mirror as the object is in front.

APPLICATIONS OF REFLECTION

lizellexs — 2021-07-20 22:04:23 UTC

PERISCOPES!

HOW A PERISCOPE WORKS

lizellexs — 2021-07-20 22:12:12 UTC

LIGHT AS A WAVE (ELECTRIC+MAGNETIC FIELD)

lizellexs — 2021-07-26 06:58:08 UTC

LIGHT = ELECTROMAGNETIC WAVES
Consists of 2 perpendicular waves:

a vertical electric field and
a horizontal magnetic field,
in phase with each other.

lizellexs — 2021-07-26 06:58:16 UTC

lizellexs — 2021-07-26 06:58:47 UTC

THE WAVE EQUATION OF LIGHT:

lizellexs — 2021-07-26 06:58:59 UTC

v = f.λ where, v is speed
f is frequency
λ is wavelength

HOW TO DERIVE THE WAVE EQUATION:
We know: speed = distance / time
For a wave: speed = wavelength / time
= λ / T
= λ x 1/T
= λ x f
v = fλ

EM SPECTRUM

lizellexs — 2021-07-26 07:57:15 UTC

Radiation of all frequencies travels at the same velocity through space. The speed of light in vacuum, c, is equal to 3 x 10⁸ m.s⁻¹.

The wavelength and frequency of these waves can be calculated using the wave equation,
c = f λ
where c is the speed of light = 3 x 10⁸ m.s⁻¹
f is the frequency measured in hertz (Hz)
λ is wavelength measured in metres (m)

Refraction of light - ray diagram

lizellexs — 2021-07-26 07:58:07 UTC

Real vs apparent depth

T.I.R. = TOTAL INTERNAL REFLECTION

lizellexs — 2021-07-26 07:58:28 UTC

TOTAL INTERNAL REFLECTION = the complete reflection of a light ray reaching an interface with a less dense medium when the angle of incidence exceeds the critical angle.
CRITICAL ANGLE = the size of an incident angle that produces a refracted angle of 90°.
2 CONDITIONS UNDER WHICH T.I.R OCCURS:
- Light must travel from more dense to less dense medium.
- Angle of incidence must be BIGGER THAN CRICITAL ANGLE of the light beam.

Uses of TIR - Optical fibers

lizellexs — 2021-07-26 07:58:36 UTC

TIR - APPLICATION IN MIRAGES

lizellexs — 2021-07-26 07:58:43 UTC

EXERCISE - T.I.R

lizellexs — 2021-07-26 07:59:00 UTC

lizellexs — 2021-07-26 07:59:13 UTC

lizellexs — 2021-07-26 07:59:28 UTC

Some more definitions

lizellexs — 2021-07-26 08:00:32 UTC

Refractive index = the ratio of the speed of light in a vacuum to its speed in a refractive material, where bending of a ray of light occurs when passing from a medium into another with different density.
Optical density = a measure of the refracting power of a medium.
Total internal reflection = the complete reflection of a light ray reaching an interface with a less dense medium, when the angle of incidence exceeds the critical angle.
Critical angle = The angle of incidence where the angle of refraction is 90°.
Normal = the line that is perpendicular to the plane of the surface.
c = 299 792 458 m.s^-1 ≃ 3 x 10⁸m.s^-1

lizellexs — 2021-07-26 08:00:47 UTC

NOTES - LENSES (this section of lenses is not examined)

lizellexs — 2021-07-26 08:01:32 UTC

HOMEWORK

lizellexs — 2021-07-26 08:04:22 UTC

LIGHT WORKSHEET

MAGNIFYING GLASS VS TORCH

lizellexs — 2021-08-03 09:27:26 UTC

lizellexs — 2021-08-04 09:42:46 UTC

lizellexs — 2021-08-04 09:47:00 UTC

OBJECTS LOOK MORE SHALLOW IN WATER DUE TO REFRACTION

lizellexs — 2021-08-06 08:16:59 UTC

lizellexs — 2021-08-06 08:19:38 UTC

2 PROPERTIES OF WAVE CHANGES WHEN LIGHT ENTERS GLASS:

Speed of light wave DECREASES
Wavelength of light wave DECREASES
Because frequency stays constant
by v=f.lamba

lizellexs — 2021-08-06 08:21:16 UTC

lizellexs — 2021-08-06 08:22:03 UTC

lizellexs — 2021-08-06 08:22:22 UTC

lizellexs — 2021-08-06 08:23:08 UTC

lizellexs — 2021-08-06 08:23:44 UTC

lizellexs — 2021-08-06 08:24:08 UTC

COLOUR AND LIGHT

lizellexs — 2021-08-16 11:40:33 UTC

HOW RAIN DROPS REFRACT LIGHT TO FORM A RAINBOW

lizellexs — 2021-08-17 06:21:50 UTC

HOW A PRISM REFRACTS LIGHT INTO ROYGBIV - DISPERSION

lizellexs — 2021-08-17 06:23:25 UTC

PRISMS AND DISPERSION

lizellexs — 2021-08-17 06:24:39 UTC

HOW A RAINDROP FORMS A RAINBOW - VIA DISPERSION OF LIGHT

lizellexs — 2021-08-17 12:35:14 UTC

COLOUR NOTES - not examined now in June exam

lizellexs — 2021-08-17 12:37:49 UTC

SIMULATIONS - ALL LIGHT WAVE PHENOMENA

lizellexs — 2021-08-17 14:34:49 UTC

lizellexs — 2021-08-18 09:42:25 UTC

TEST PREP - LIGHT AND LENSES

lizellexs — 2021-08-20 10:13:30 UTC

MEMO

lizellexs — 2021-08-20 10:13:40 UTC

COLOUR - HOW DO WE SEE SPECIFIC COLOUR?

lizellexs — 2022-05-09 11:49:48 UTC

They absorb ROYBIV
They reflect G

REFRACTION OF LIGHT THROUGH A PRISM

lizellexs — 2022-07-20 06:22:47 UTC

FILTERS

lizellexs — 2022-08-24 08:29:24 UTC

Lens filters are transparent

FILTERS VIDEO - SUBTRACTIVE COLOURATION (SELECTIVE ABSORBTION)

lizellexs — 2022-08-24 08:32:53 UTC

COMPLIMENTARY COLOURS OF LIGHT

lizellexs — 2022-08-24 08:52:40 UTC

Complementary pairs of light colors are those colors that are exactly opposite each other on the diagram:

red and cyan
magenta and green
blue and yellow

RGB = PRIMARY COLOURS OF LIGHT

lizellexs — 2023-07-19 09:19:37 UTC

Total internal reflection through prisms inside Binoculars

lizellexs — 2023-07-24 08:24:27 UTC

HOW A SPHERICAL RAINDROP DISPERSES LIGHT

lizellexs — 2023-07-26 07:56:48 UTC

REFRACTION OF LIGHT THROUGH A PRISM

lizellexs — 2023-07-26 08:00:42 UTC

lizellexs — 2023-07-26 08:16:15 UTC

lizellexs — 2025-04-23 14:03:17 UTC

light

TIR of a laser beam in stream of water

lizellexs — 2025-04-23 14:13:17 UTC