Ask while they play

Point to each sensor. When did it see dark?

Spot it at home

• Robot vacuums have little light sensors under the front that look down to stop them falling down stairs.

Why would a robot need two line sensors, not one?

How it helps a robot

• The mBlock app calls the line sensors a line follower sensor.

Talk about it later

Hold two fingers on either side of a line. Which finger is on it?