Worksheet, Class 6, Chapter 6

 1. Which of the following changes cannot be reversed?

(a) Blowing of a balloon
(b) Folding a paper to make a toy aeroplane
(c) Rolling a ball of dough to make roti
(d) Baking cake in an oven
(e) Drying a wet cloth
(f) Making biogas from cow dung
(g) Burning of a candle

2. The iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel because on heating the iron rim

(a) expands and fits onto the wooden wheel
(b) contracts and fits onto the wooden wheel
(c) no change in the size takes place
(d) expands first, then on cooling contracts and fits onto the wooden wheel. 

3.  Give one example in each case:

(a) Change which occurs on heating but can be reversed.

(b) Change which occurs on heating but cannot be reversed.
(c) Change which occurs on cooling but can be reversed.
(d) Change which occurs on mixing two substances, but can be reversed.
(e) Change which occurs on mixing two substances, but cannot be reversed.