physics unit tesst

Define and provide an example of light

A form of energy that travels as electromagnetic waves and allows us to see (e.g., sunlight).

Define and provide an example of electromagnetic waves

Waves that can travel through empty space (e.g., light from the Sun reaching Earth).

Define and provide an example of a medium

A material that light travels through (e.g., air, water, glass).

Define and provide an example of white light

Light made of all colours combined (e.g., sunlight).

Define and provide an example of visible light

The part of the electromagnetic spectrum humans can see (ROYGBIV).

Define and provide an example of luminous

Objects that produce their own light (e.g., the Sun, a lightbulb).

Define and provide an example of non-luminous

Objects that reflect light but don’t produce it (e.g., a book, the Moon).

Define and provide an example of transparent

Lets light pass through clearly (e.g., clean glass).

Define and provide an example of translucent

Lets some light through but scatters it (e.g., frosted glass).

Define and provide an example of opaque

Does not let light through (e.g., wood).

Define and provide an example of specular reflection

Reflection from a smooth surface, producing a clear image (e.g., mirror).

Define and provide an example of diffuse reflection

Reflection from a rough surface, scattering light (e.g., paper).

What is Incandescence

Light from heat (e.g., glowing filament in a bulb).

What is electric discharge

Light from electricity passing through gas (e.g., neon signs).

What is phosphorescence

Light emitted slowly after absorbing energy (e.g., glow-in-the-dark stars).

What is fluorescence

Light emitted immediately after absorbing energy (e.g., fluorescent lights).

What is Chemiluminescence

Light from a chemical reaction (e.g., glow sticks).

What is bioluminescence

• Light from living organisms (e.g., fireflies).

Triboluminescence

Light from friction or crushing (e.g., crushing sugar crystals).

LED (Light Emitting Diode)

Light produced by electric current in a semiconductor (e.g., LED bulbs).

How does a prism cause the dispersion of light?

A prism separates white light into colours because each colour bends (refracts) at a different angle when passing through the prism due to different wavelengths.

What is a laser? What are its properties?

Answer:
A laser is a device that produces a focused beam of light.
Properties:

• Monochromatic (one colour)

• Coherent (waves are in sync)

• Directional (travels in a straight, narrow beam)

What is reflection? What are the two laws of reflection?

Answer:
Reflection is when light bounces off a surface.
Laws:

1. Angle of incidence = angle of reflection

2. The incident ray, reflected ray, and normal all lie in the same plane

What is a real image? How is it different from a virtual image?

A real image is formed when light rays actually meet and can be projected on a screen. A virtual image is formed when light rays only appear to meet and cannot be projected (like in a mirror).

Why are concave mirrors used for makeup? Where must they be held? What if too far?

Concave mirrors magnify the image when the object is between the mirror and the focus. They must be held close (inside the focal point). If held too far, the image becomes inverted and smaller.

Why are convex mirrors used for security and cars?

Convex mirrors spread light out, giving a wider field of view. This lets you see more area, which is useful for security and reducing blind spots in cars (but images appear smaller).

Define refraction. Why does it occur?

Refraction is the bending of light when it passes from one medium to another. It occurs because light changes speed in different materials.

Describe refraction (fast → slow and slow → fast)

• Fast → slow medium (e.g., air → water): light slows down and bends toward the normal

• Slow → fast medium (e.g., water → air): light speeds up and bends away from the normal
  (Skipped diagram, but that’s the rule to remember)

What is index of refraction? What do the numbers mean? (water 1.33, glass 1.52)

Answer:
The index of refraction (n) tells how much light slows down in a material.

• Water (1.33): light slows a bit

• Glass (1.52): light slows more

If light goes from water → glass, it slows down more and bends toward the normal.

What is the critical angle?

The critical angle is the angle of incidence in the denser medium where the refracted ray travels along the surface (90°). Beyond this angle, total internal reflection happens.

What is total internal reflection? Uses?

Answer:
Total internal reflection is when light reflects completely inside a medium instead of refracting out.

Uses:

• Diamonds: light reflects inside, making them sparkle

• Fibre optics: light carries data through cables

• Retro-reflectors: reflect light back to its source (e.g., road signs)

What is apparent depth?

Apparent depth is when objects under water look closer to the surface than they actually are because light bends away from the normal when it leaves water.

Why do mirages form?

Mirages form because layers of air at different temperatures have different densities, which bend light. Hot air near the ground makes light bend upward, creating the illusion of water.

How is a rainbow formed? What type of image is it?

A rainbow forms when sunlight enters raindrops, gets refracted, reflected inside the drop, and refracted again as it exits, separating into colours.
A rainbow is a virtual image because the light doesn’t actually come from a physical object at that location.

Define converging lens and diverging lens + lens terms

Answer:

• Converging lens (convex): A lens that brings parallel light rays together at a point (focus).

• Diverging lens (concave): A lens that spreads light rays apart.

Lens terms:

• Optical center: The middle of the lens where light passes straight through without bending

• Principal axis: A straight line through the optical center

• Principal focus (F): Point where parallel rays meet (converging) or appear to come from (diverging)

• Secondary principal focus: Same as F but on the opposite side of the lens

• The principal focus of a ??? is on the opposite side of the lens as the incident rays.

• The principal focus of a ??? is on the same side of the lens as the incident rays.

• The principal focus of a converging lens is on the opposite side of the lens as the incident rays.

• The principal focus of a diverging lens is on the same side of the lens as the incident rays.

Why can converging lenses form real images but diverging lenses cannot?

Converging lenses bring light rays together so they actually meet, forming a real image. Diverging lenses spread rays apart, so they never meet—only appear to come from a point, making only virtual images.

Imaging rules for a converging lens

Answer:
Use these 3 main rays:

• Ray parallel to axis → refracts through focus

• Ray through focus → refracts parallel

• Ray through optical center → goes straight

Where the rays meet = image location, then use SALT:

• Size

• Attitude (upright/inverted)

• Location

• Type (real/virtual)

Difference between virtual images (converging vs diverging lens)

A virtual image from a converging lens is formed only when the object is inside the focal point and is usually larger. A virtual image from a diverging lens is always formed, and it is always smaller and upright.

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