Question

Record your answer using the audio recorder. If your mic is broken, please call me with the answer or webmail the answer to me.

Suppose you were stranded on a desert island with only a convex lens and a mirror. Describe how you could use EACH of these tools to signal for help.

(2 points)

Answer 1

I can’t make an audio recording or call/email you, but here’s the answer in text.

Mirror:
- Use it as a heliograph: reflect sunlight toward rescuers (boats, planes) to make bright, easily seen flashes. Aim by angling the mirror until the sun’s reflection reaches the target; make repeated flashes by tilting the mirror or covering/uncovering it.
- Send SOS in Morse (… --- …) by short/long flashes to attract attention.

Convex lens:
- Use it as a magnifier to start a fire: focus sunlight to a tiny, hot spot on tinder (hold the lens at about its focal distance) until it ignites. Then use the resulting flame/smoke as a signal (smoke by day, fire light by night).
- Alternatively, if you can’t make tinder catch, you can form a small, very bright spot of sunlight on a surface and move it to attract attention, but the primary practical use is fire-starting.

Safety notes: never look directly at the sun or at a reflected beam, and be careful not to burn yourself while focusing the lens.