What is the law of reflection for light?

The angle of incidence equals 90° minus the angle of reflection The angle of incidence equals the angle of reflection, both measured from the normal to the surface Light reflects at 90° to the surface regardless of the angle of incidence The angle of reflection is always twice the angle of incidence

A ray of light passes from air into glass and bends toward the normal. What does this tell us?

Light has sped up — faster light bends toward the normal Light has slowed down — it moves more slowly in glass than in air, causing it to bend toward the normal The glass is attracting the light gravitationally Glass has a negative charge that deflects the light

What is total internal reflection, and what is it used for?

Light reflects completely off the outside of a mirror — used in telescopes When light in a dense medium hits a boundary at an angle greater than the critical angle, it reflects completely back — used in optical fibres to transmit data as pulses of light Light is absorbed entirely by black surfaces — used to prevent light leakage in cameras When light hits a surface perpendicularly it reflects completely — used in laser cavities

Why does a glass prism split white light into a rainbow of colours?

The prism reflects different colours at different angles Different colours travel at different speeds in vacuum and separate at the prism surface Different colours (frequencies) of light are refracted by slightly different amounts in glass — violet bends most, red bends least The prism filters out certain colours using its crystalline structure

How does a rainbow form?

Sunlight reflects off flat water surfaces and spreads into different colours Sunlight enters a water droplet, refracts and disperses, reflects off the back, and refracts again on exit — each colour emerges at a slightly different angle Water droplets filter out some wavelengths, leaving only the rainbow colours visible Rainbows occur only when sunlight is at exactly 90° to the observer's line of sight

Thomas Young performed his famous double-slit experiment in 1801. What did he observe?

Light passing through two slits produced exactly two bright lines on the screen — confirming that light is made of particles Light passing through two narrow slits produced alternating bright and dark bands (interference fringes) on a screen — proving light is a wave Two slits blocked some light, making the screen dimmer than with one slit Light from the two slits travelled at different speeds, creating a colour pattern

In Young's double-slit experiment, what causes the bright fringes?

Diffraction — light bends around both slits and focuses at regular intervals Constructive interference — light from both slits arrives in phase, so the waves add to produce maximum brightness Reflection — light bounces between the two slits to produce a standing wave Refraction — light bends at the slits and converges on bright spots

In Young's double-slit experiment, what causes the dark fringes?

The two slits block light in alternating sections Destructive interference — light from both slits arrives exactly out of phase, so the waves cancel Light is absorbed by the screen material in regular bands The slit edges cast sharp shadows that create dark regions

If the slit separation in a double-slit experiment is reduced, what happens to the fringe spacing?

The fringes become closer together The fringes disappear completely The fringes become further apart — smaller slit separation produces wider interference fringes The pattern changes from fringes to two bright spots

Young's double-slit experiment conclusively proved light is a wave in the 19th century. Why is this same experiment even more puzzling when performed with individual photons one at a time?

Single photons always go through one slit only, so the interference pattern disappears Single photons are too dim to produce an interference pattern — you need a beam Even single photons, fired one by one, gradually build up an interference pattern — implying each photon somehow 'goes through both slits' and interferes with itself Single photons travel slower and refract more, changing the pattern into two bright spots