Opticas (Unit 1)
The Nature of Light
Light as Energy:
- Light is a type of energy that can travel through empty space.
- It moves in the form of electromagnetic (EM) waves, which have electric and magnetic field
components.
Electromagnetic Waves:
- Most EM waves are invisible, except for visible light (ROYGBIV).
- Different EM waves have different wavelengths, frequencies, and energy.
Interaction of Light with Objects:
- Reflection: Light bounces off surfaces. Smooth surfaces reflect light clearly, while rough
surfaces scatter it.
- Absorption: Light is converted into heat and no longer visible. Dark surfaces absorb more light.
- Transmission: Light passes through objects.
- Transparent: Most light passes through.
- Translucent: Some light passes but scatters.
- Opaque: No light passes through.
Speed of Light:
- Light travels at 3.00 × 10⁸ m/s in a vacuum.
- The speed formula: c = fλ, where c is speed of light, f is frequency, and λ is wavelength.
Wavelength and Frequency:
- Wavelength is the distance between peaks of a wave.
- Frequency is the number of wave oscillations per second (measured in Hz).
- Higher frequency = shorter wavelength = more energy.
Visible Light Wavelengths:
- Red: 622–780 nm
- Orange: 597–622 nm
- Yellow: 577–597 nm
- Green: 492–577 nm
- Blue: 455–492 nm
- Violet: 390–455 nm
,Reflection & plane mirrors (9/10/24)
- Light travels in a straight line, in the same directions
- Reflection is the change of direction of a wave.
Fermat principle:
- Light follows the path that will take the least amount of time when traveling from one point to
another
Laws of reflection:
1. The angle of reflection is equal to the angle of incidence.
● Imagine a laser pointer shining light onto a flat mirror. If the laser beam hits the mirror
at a 30° angle to the normal (a perpendicular line to the mirror's surface), the reflected
light will bounce off at the same 30° angle on the other side of the normal. This
demonstrates the first law that the angle of incidence equals the angle of reflection.
2. The incidence ray, reflected ray, and the normal (perpendicular line to the surface) all lie on the
same plane.
● If you shine a flashlight onto a smooth, flat surface like a mirror or glass table, the light
beam (incident ray) striking the surface, the reflected light beam (reflected ray), and the
normal line all lie in the same two-dimensional plane. This means they don't deviate
from the flat surface and stay aligned in one space.
3. Any ray of light that travels along a normal is reflected straight back
● If you shine a laser pointer directly perpendicular to a mirror (meaning the beam is
aligned with the normal), the light will reflect straight back along the same path. This
is like shining a flashlight directly into a mirror and having the light return directly to
your eyes.
,Ray Diagrams and Plane Mirrors (9/13/24)
1. Incident Ray:
- Draw a ray from point A to the mirror at a 90-degree angle.
2. Angled Ray:
- Draw another ray from point A at an angle, and measure the angle of incidence.
- Angle of reflection = angle of incidence.
3. Image Creation:
- Extend the reflected rays behind the mirror until they meet (this is where the image forms).
- Label the point where they meet as Ai (for point A’s image).
4. Repeat for Point B:
- Follow the same steps for point B to find Bi (B's image).
LOST (Image Characteristics):
- L: Location (distance from mirror).
- O: Orientation (upright or inverted).
- S: Size (same, smaller, or larger).
- T: Type (virtual image).
Types of Light
Light Production:
- Atoms absorb energy and become excited. They release this energy in the form of light.
Term Definition Examples
Incandescence Light emitted due to high Incandescent bulb, lava,
temperature of a material. campfire
Fluorescence Light emitted when exposed to Invisible ink, highlighter, fish
ultraviolet light. tanks
Luminescence Light emitted without heating TV screens, LED lights
the substance.
, Phosphorescence Light continues to be emitted Glow-in-the-dark stickers, toys
even after exposure to
ultraviolet light is stopped.
Chemiluminescence Light produced from a chemical Glow sticks, luminol (used in
reaction without heat. forensics)
Bioluminescence Light from a biochemical Jellyfish, fireflies, anglerfish
reaction in living organisms.
Triboluminescence Light emitted when crystals are Wintergreen Lifesavers, sugar
broken or stressed. crystals
Differences Between Light Types:
- Fluorescence vs. Phosphorescence: Fluorescence stops immediately after the light source is removed,
while phosphorescent materials continue to glow for hours.
- Fluorescence vs. Bioluminescence: Fluorescence comes from absorbing energy from an external
source, while bioluminescence results from a chemical reaction in a living organism.
Electric Discharge:
- Definition: Electric charge transmitted from one body to another.
- Difference from Incandescent Bulb:
- Electric discharge bulbs send electricity through gas or vapor.
- Incandescent bulbs heat metal (like tungsten) to produce light.
- Difference from Fluorescent Bulb:
- Fluorescent bulbs produce light using mercury vapor and ultraviolet radiation.
- Electric discharge bulbs create an electric arc in the gas inside.
Convex & Concave Mirrors
● Concave mirror - reflecting surface curves inward
Centre of Curvature (C):
- Point at which all normal meet
- Centre of circle
The Nature of Light
Light as Energy:
- Light is a type of energy that can travel through empty space.
- It moves in the form of electromagnetic (EM) waves, which have electric and magnetic field
components.
Electromagnetic Waves:
- Most EM waves are invisible, except for visible light (ROYGBIV).
- Different EM waves have different wavelengths, frequencies, and energy.
Interaction of Light with Objects:
- Reflection: Light bounces off surfaces. Smooth surfaces reflect light clearly, while rough
surfaces scatter it.
- Absorption: Light is converted into heat and no longer visible. Dark surfaces absorb more light.
- Transmission: Light passes through objects.
- Transparent: Most light passes through.
- Translucent: Some light passes but scatters.
- Opaque: No light passes through.
Speed of Light:
- Light travels at 3.00 × 10⁸ m/s in a vacuum.
- The speed formula: c = fλ, where c is speed of light, f is frequency, and λ is wavelength.
Wavelength and Frequency:
- Wavelength is the distance between peaks of a wave.
- Frequency is the number of wave oscillations per second (measured in Hz).
- Higher frequency = shorter wavelength = more energy.
Visible Light Wavelengths:
- Red: 622–780 nm
- Orange: 597–622 nm
- Yellow: 577–597 nm
- Green: 492–577 nm
- Blue: 455–492 nm
- Violet: 390–455 nm
,Reflection & plane mirrors (9/10/24)
- Light travels in a straight line, in the same directions
- Reflection is the change of direction of a wave.
Fermat principle:
- Light follows the path that will take the least amount of time when traveling from one point to
another
Laws of reflection:
1. The angle of reflection is equal to the angle of incidence.
● Imagine a laser pointer shining light onto a flat mirror. If the laser beam hits the mirror
at a 30° angle to the normal (a perpendicular line to the mirror's surface), the reflected
light will bounce off at the same 30° angle on the other side of the normal. This
demonstrates the first law that the angle of incidence equals the angle of reflection.
2. The incidence ray, reflected ray, and the normal (perpendicular line to the surface) all lie on the
same plane.
● If you shine a flashlight onto a smooth, flat surface like a mirror or glass table, the light
beam (incident ray) striking the surface, the reflected light beam (reflected ray), and the
normal line all lie in the same two-dimensional plane. This means they don't deviate
from the flat surface and stay aligned in one space.
3. Any ray of light that travels along a normal is reflected straight back
● If you shine a laser pointer directly perpendicular to a mirror (meaning the beam is
aligned with the normal), the light will reflect straight back along the same path. This
is like shining a flashlight directly into a mirror and having the light return directly to
your eyes.
,Ray Diagrams and Plane Mirrors (9/13/24)
1. Incident Ray:
- Draw a ray from point A to the mirror at a 90-degree angle.
2. Angled Ray:
- Draw another ray from point A at an angle, and measure the angle of incidence.
- Angle of reflection = angle of incidence.
3. Image Creation:
- Extend the reflected rays behind the mirror until they meet (this is where the image forms).
- Label the point where they meet as Ai (for point A’s image).
4. Repeat for Point B:
- Follow the same steps for point B to find Bi (B's image).
LOST (Image Characteristics):
- L: Location (distance from mirror).
- O: Orientation (upright or inverted).
- S: Size (same, smaller, or larger).
- T: Type (virtual image).
Types of Light
Light Production:
- Atoms absorb energy and become excited. They release this energy in the form of light.
Term Definition Examples
Incandescence Light emitted due to high Incandescent bulb, lava,
temperature of a material. campfire
Fluorescence Light emitted when exposed to Invisible ink, highlighter, fish
ultraviolet light. tanks
Luminescence Light emitted without heating TV screens, LED lights
the substance.
, Phosphorescence Light continues to be emitted Glow-in-the-dark stickers, toys
even after exposure to
ultraviolet light is stopped.
Chemiluminescence Light produced from a chemical Glow sticks, luminol (used in
reaction without heat. forensics)
Bioluminescence Light from a biochemical Jellyfish, fireflies, anglerfish
reaction in living organisms.
Triboluminescence Light emitted when crystals are Wintergreen Lifesavers, sugar
broken or stressed. crystals
Differences Between Light Types:
- Fluorescence vs. Phosphorescence: Fluorescence stops immediately after the light source is removed,
while phosphorescent materials continue to glow for hours.
- Fluorescence vs. Bioluminescence: Fluorescence comes from absorbing energy from an external
source, while bioluminescence results from a chemical reaction in a living organism.
Electric Discharge:
- Definition: Electric charge transmitted from one body to another.
- Difference from Incandescent Bulb:
- Electric discharge bulbs send electricity through gas or vapor.
- Incandescent bulbs heat metal (like tungsten) to produce light.
- Difference from Fluorescent Bulb:
- Fluorescent bulbs produce light using mercury vapor and ultraviolet radiation.
- Electric discharge bulbs create an electric arc in the gas inside.
Convex & Concave Mirrors
● Concave mirror - reflecting surface curves inward
Centre of Curvature (C):
- Point at which all normal meet
- Centre of circle
