Unit 10: Light and Optics
Light bouncing, bending, splitting into color, and bending again through a lens until an image appears somewhere it never physically sits.
11 topics · 36 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
The Electromagnetic Spectrum
- How it worksHow does changing only the wavelength turn the same electromagnetic wave from radio into visible light into gamma rays?
- Common mistakeWhy isn't visible light the only part of the electromagnetic spectrum that actually exists?
- Going furtherWhat happens to a wave's energy as its position on the electromagnetic spectrum shifts toward shorter wavelengths?
Your turn1 of 2
A doctor's X-ray machine and a kitchen microwave oven seem to do completely different jobs, imaging bones and heating food, yet physicists classify both as the exact same fundamental kind of wave. Why can a doctor's X-ray machine and a kitchen microwave both be described as the exact same kind of wave?Reflection of Light
- How it worksHow does the law of reflection make the angle a light ray bounces off always equal the angle it came in at?
- Worked exampleFind the angle of reflection of a light ray hitting a flat mirror at 35 degrees from the normal.
- Common mistakeWhy isn't the image in a flat mirror actually located inside the glass itself?
Your turn1 of 2
Find the angle of reflection of a light ray hitting a flat mirror at 62 degrees from the normal.Refraction and Snell's Law
- How it worksHow does light bend when it slows down crossing into a denser material like water or glass?
- Worked exampleFind the angle of refraction for light entering water at 40 degrees, going from air with n=1.00 into water with n=1.33.
- Common mistakeWhy doesn't light traveling straight into a surface at zero degrees bend at all?
- Going furtherWhat happens to the bend in a light ray when it passes into a material with an even higher index of refraction?
Your turn1 of 2
Find the angle of refraction for light traveling from air (n = 1.00) into a medium with index of refraction 1.94, hitting the boundary at 57 degrees from the normal.Total Internal Reflection
- How it worksHow does light hitting a boundary beyond the critical angle reflect completely instead of refracting through?
- Worked exampleFind the critical angle for light traveling from glass with n=1.5 into air with n=1.0.
- Going furtherWhat happens to a light ray inside an optical fiber the moment it strikes the wall below the critical angle?
Your turn1 of 2
Find the critical angle for light traveling from a medium with index of refraction 2.07 into a medium with a lower index of refraction 1.188.Converging and Diverging Lenses
- How it worksHow does the curved shape of a converging lens bend parallel light rays inward to meet at a focal point?
- Common mistakeWhy doesn't a diverging lens ever form a real image the way a converging lens can?
- Going furtherWhat happens to the focal point of a lens when its curvature is made sharper?
Your turn1 of 2
Sunlight passing through a magnifying glass on a sunny day converges into a single, intensely bright and hot point of light on the ground below, rather than staying spread out the way it was before passing through the lens. Why does a magnifying glass bend light from every direction into one single bright point?Ray Diagrams for Lenses
- How it worksHow do three simple principal rays traced through a lens locate exactly where an image forms?
- Worked exampleFind the image distance for an object placed 30 cm from a converging lens with a 10 cm focal length.
- Worked exampleFind the image distance for an object placed 5 cm from a converging lens with a 10 cm focal length, forming a virtual, upright image.
- Common mistakeWhy isn't the image formed by a lens sitting exactly where the light rays visibly cross on the object's own side?
Your turn1 of 2
Find the image distance for an object placed 73 cm from a converging lens with a 7 cm focal length.Curved Mirrors and Ray Diagrams
- How it worksHow does a concave mirror curve light rays inward to form a real image you can project onto a screen?
- Worked exampleFind the image distance for an object placed 20 cm from a concave mirror with a 15 cm focal length.
- Worked exampleFind the image distance for an object placed 10 cm from a concave mirror with a 15 cm focal length, forming a magnified virtual image.
- Common mistakeWhy doesn't a convex mirror ever form a real, upside-down image no matter where the object is placed?
Your turn1 of 2
Find the image distance for an object placed 74 cm from a concave mirror with a 11 cm focal length.The Eye and Vision Correction
- How it worksHow does the eye's own lens change shape to focus objects at different distances onto the retina?
- Common mistakeWhy isn't nearsightedness caused by a weak eye lens that simply needs more light?
- Going furtherWhat happens to where an image lands on the retina when the eyeball itself is slightly too long?
Your turn1 of 2
Glasses prescribed for a nearsighted person are noticeably thin right in the middle and thicker toward the edges, while glasses for a farsighted person bulge outward, thicker in the middle, the opposite lens shape entirely. Why do glasses for a nearsighted person look thin in the middle while glasses for farsightedness bulge outward?Color and Light Mixing
- How it worksHow does an object's color come from which wavelengths of light it reflects and which it absorbs?
- Common mistakeWhy doesn't a red shirt actually contain a red pigment that glows on its own in the dark?
- Going furtherWhat color does a blue object appear to be under a light source that emits only red light?
Your turn1 of 2
Shining a red spotlight and a green spotlight onto the same spot on a white wall produces a surprising yellow glow, yet mixing red and green paint together on a palette instead produces a dull, muddy brown color, the opposite kind of result. Why does mixing red and green light make yellow, while mixing red and green paint makes brown?Dispersion and the Rainbow
- How it worksHow does each wavelength of light bend by a slightly different amount inside a prism, fanning white light into a spectrum?
- Common mistakeWhy isn't a rainbow created by any kind of paint or dye inside the raindrops?
- Going furtherWhat happens to the order of colors in a rainbow when sunlight reflects a second time inside the same raindrop?
Your turn1 of 2
White sunlight passing through a triangular glass prism spreads out into a full rainbow-like band of separate colors on the other side, even though the light entering the prism looked like one single uniform white beam. Why does white light split into a full rainbow of colors after passing through a glass prism?Polarization of Light
- How it worksHow does a polarizing filter only let through light waves vibrating in one direction and block the rest?
- Common mistakeWhy doesn't ordinary light already vibrate in just one single direction before it hits a polarizer?
- Going furtherWhat happens to light passing through two polarizing filters as the second one is rotated to 90 degrees from the first?
Your turn1 of 2
Polarized sunglasses dramatically cut down the harsh glare reflecting off a lake's surface, yet those same sunglasses often do almost nothing to reduce glare from certain tilted phone or tablet screens viewed at an angle. Why do polarized sunglasses cut glare off a lake but do almost nothing to cut glare from some tilted phone screens?