PDF chapter test TRY NOW
Invisible letters:
- Take a lemon, a paintbrush and a piece of paper.
- Cut the lemon and squeeze out its juice in a cup.
- Dip the brush in the lemon juice and write a message on the paper.
- Let the paper dry and you find that the letters of your message become invisible.
- Now, press the paper with hot iron or warm it by holding it above the flame of a candle (Take care that it does not catch fire).
- As the paper gets warm, invisible letters change into dark brown colour.
Identify the changes that can be reversed in this process.
Reversible change:
Irreversible change:
Answer variants:
Taking a paintbrush
Wetting of paper
Writing message on paper
Drying of paper
Squeezing lemon
Cutting lemon
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