The Bending Trick

Why it matters

The straw in your glass looks snapped at the waterline. Take it out: perfectly straight. The straw never bent — the LIGHT did, right at the border between water and air.

The idea in plain words

The border rules — in plain words. Tap each.

denser: toward the normal · rarer: away from it

A ray passes through a rectangular glass slab (in one face, out the opposite one). How does it emerge?

It emerges PARALLEL to how it entered — just shifted sideways

• the event: refraction — the bending of light where it crosses into a new medium — because its SPEED changes there
• the strength: μ (refractive index) — a number for how strongly a medium bends light: water 1.33, glass 1.5, diamond 2.42 — bigger bends harder
• the exception: no-bend case — a ray along the normal (i = 0°) goes straight through — slower, but unbent
• Entering: bends TOWARD the normal
• Leaving: bends AWAY by the same amount

Predict first

Light entering glass from air bends…

Denser medium, slower light, bend TOWARD the normal. Leaving the glass, it speeds up and bends away — the two rules of every border crossing.

• towards the normal — it slows down in the denser medium — correct
• away from the normal
• not at all — glass is transparent

What you do

Aim the ray into water, glass and diamond — the denser the medium, the sharper the lane change.

Check yourself

Refraction happens because light…

Different medium, different speed — the direction change is the visible symptom.

Light travels FASTEST in…

Denser media slow light — diamond slows it to less than half speed.

Leaving water into air, a light ray bends…

Speeding up on exit, the ray leans away — the exact reverse of entering.

• changes speed between media — correct
• is heavier in glass
• gets absorbed and re-made
• vacuum (or air) — correct
• glass
• diamond
• away from the normal — correct
• towards the normal
• backwards