Lesson 1 · The Reflectance Sensor — Knowledge ChecksAnswer key

Your sensor reads 0.8. What is it most likely over?

1. A.A white surface
2. B.A black line✓
3. C.The edge of the line
4. D.Nothing — that value is impossible

High values (near 1.0) mean little light came back — a dark surface absorbs it. White gives low values near 0.0.

Your 'off line' (white) values average 0.2 and your 'on line' (black) values average 0.8. What threshold should you choose?

1. A.0.2
2. B.0.5✓
3. C.0.8
4. D.1.0

Halfway between 0.2 and 0.8 is 0.5. A reading above it means the line; below it means white.

Why does the XRP have two reflectance sensors instead of one?

1. A.As a spare in case one breaks
2. B.So it can tell which side of the line it is on✓
3. C.To read the line twice as fast
4. D.One reads white, the other reads black

Two independent readings let the robot tell whether it's drifting left or right of the line — essential for following it later.