NCERT Solutions for Class 8th Science Chapter 8 .1.1 Is air a mixture? — Activity 8.2: Let us explore
Book page 1198 Updated on2026-09-19
Q1.
Place the black sheet of paper undisturbed near an open window (Fig. 8.6a), or in the garden, for a few hours. What do you observe?Fig. 8.6, page 119 — redrawn sketch. The black sheet of paper left at an open window: (a) with no dust particles; (b) with dust particles, examined through a magnifying glass.
Answer
Tiny particles have settled on the surface of the sheet. Under a magnifying glass (Fig. 8.6b) you can see that they are of different sizes, shapes and colours — fine grey dust, specks of soot, bits of pollen, a stray fibre of cloth.
Sheet
Observation
Fig. 8.6a — at the start
Black, clean, free of any visible dust particle
Fig. 8.6b — after a few hours
Small particles settled all over the surface
Why it happens: These particles were floating in the air all along. Once the sheet lies undisturbed, the particles slowly settle on it under gravity and stay there. This shows that dust particles are suspended in the air. A black sheet is chosen deliberately — light-coloured dust shows up clearly against a dark background.
Check it yourself: Repeat the activity with one sheet near a busy road and one inside a closed room. The difference in the amount of dust tells you why the number of dust particles varies from place to place.