Unit 3: Optics

Question 1

Incandescence

Answer 1

The process of emitting light because of high temperature (light bulbs)

Question 2

Electric discharge

Answer 2

The process of emitting light because of electricity passing through a gas (neon lights)

Question 3

Fluorescence

Answer 3

The process of emitting visible light after absorbing radiation that is not normally visible (fluorescent stickers)

Question 4

Phosphorescence

Answer 4

The process of emitting light for some time after absorbing radiation from another source (Sticker/ stars on wall that continue to shine after lights are off)

Question 5

Triboluminescence

Answer 5

The mechanical breaking of bonds in a compound releases light energy (wintergreen lifesavers, candy)

Question 6

Chemiluminescence

Answer 6

Light given off by a chemical reaction (glow sticks)

Question 7

Bioluminescence

Answer 7

Chemiluminescence in a living organism (Some algae, jellyfish)

Question 8

Properties of Light

Answer 8

Light is electromagnetic radiation that can be detected by the human eye. It is made up of photos and travels in one direction within one medium. It travels at almost 300,000 km/second. Light travels in straight lines.
Light travels fast – about 3.0 × 10⁸ m/s in a vacuum.
Light reflects and refracts – changes direction when bouncing off or passing through materials.
Light is a form of energy – it can be absorbed, reflected, transmitted, or refracted.

Question 9

Electromagnetic Spectrum

Answer 9

Waves transmit energy, produced by charged particles. They have electrical and magnetic properties and travel at a constant speed. The number of crests per second it the frequency.

Question 10

Laws of Reflection

Answer 10

Angle of incidence = Angle of reflection
Incident ray, reflected ray, and normal lie on the same plane

Question 11

Image Characteristics in a Plane Mirror

Answer 11

Same size
Same distance behind the mirror as object is in front
Upright
Virtual (can’t be projected onto a screen)
Laterally inverted (left and right are switched)

Question 12

Refraction

Answer 12

Definition:
Refraction is the bending of light as it passes from one medium to another due to a change in speed.

Key Rules:
Light slows down and bends toward the normal in a more dense medium (e.g., air → water).

Light speeds up and bends away from the normal in a less dense medium (e.g., water → air).

Index of Refraction:
𝑛=𝑐/𝑣
n = index of refraction
c = speed of light in vacuum (3.00 × 10⁸ m/s or 300,000,000)
v = speed of light in the medium

Question 13

Applications

Answer 13

Mirrors
Concave mirrors: used in telescopes, headlights, shaving mirrors

Convex mirrors: used for security and vehicle mirrors

B. Lenses
Converging lenses: magnifying glasses, cameras, microscopes

Diverging lenses: used in glasses for nearsightedness

C. The Human Eye
Cornea + lens refract light to focus on the retina

Ciliary muscles adjust lens shape (accommodation)

Nearsighted (myopia): image in front of retina → fixed with diverging lens

Farsighted (hyperopia): image behind retina → fixed with converging lens

Question 14

Eye

Answer 14

Step 1: Light Enters the Eye
Light from an object enters the cornea, the transparent curved outer layer.
The cornea begins to bend (refract) the light toward the retina.
🔘 Step 2: Pupil Controls Light
The light then passes through the pupil, the dark opening in the center of the eye.
The size of the pupil is controlled by the iris (colored part of the eye).
In bright light, the pupil contracts to let in less light.
In dim light, it expands to let in more light.

🔍 Step 3: The Lens Fine-Tunes Focus
Light passes through the lens, which further refracts the light to focus it on the retina.
The lens is flexible – the ciliary muscles change its shape to focus on objects at different distances:
Thinner lens = far objects
Thicker lens = close objects
This focusing is called accommodation.

🧠 Step 4: Light Hits the Retina
The retina is the inner lining at the back of the eye.
It contains photoreceptors:
Rods (for black-and-white and low light)
Cones (for color and bright light)
When light hits these cells, it’s converted into electrical signals.

⚡ Step 5: Signals Go to the Brain
These signals travel along the optic nerve to the brain, which interprets them as vision.

Answer 15

Cornea
- Transparent outer layer
- Begins bending (refracting) light into the eye
Aqueous Humor
- Clear fluid between cornea and lens
- Maintains eye pressure and shape
Pupil
- Hole in the center of the iris
- Controls how much light enters the eye
Iris
- Colored part of the eye
- Adjusts pupil size (contracts/expands)
Lens
- Flexible, clear structure
- Fine-tunes the focus of light onto the retina
Ciliary Muscles
- Change the shape of the lens for focusing (accommodation)
Vitreous Humor
- Jelly-like substance filling the eye
- Helps maintain eye shape
Retina
- Inner layer at the back of the eye
- Contains rods and cones (light sensors)
- Converts light into electrical signals
Rods
- Photoreceptors for black-and-white, low-light vision
Cones
- Photoreceptors for color and bright light
Fovea
- Center of retina with sharpest vision
- High concentration of cones
Optic Nerve
- Carries electrical signals from retina to the brain
Blind Spot
- Where the optic nerve exits the eye
- No rods or cones, so no image
Sclera
- White part of the eye
- Protects and maintains the shape of the eye