Light: Mirrors and Lenses — Science STD 8 — Question

Explain why, people are advised to use iodized salt in cooking food.

Is looking after physical health more important at adolescent age? Give your opinion.

What happens when a copper vessel is exposed to moist air for a long time?

Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table
(b) Chalk powder
(c) Cardboard surface
(d) Marble floor with water spread over it
(e) Mirror
(f) Piece of paper

How much time does light take to reach us from the Sun?

Explain why, a glass rod can be charged by rubbing when held by hand but an iron rod cannot be charged by rubbing, if held by hand.

A beaker contains an acidified copper sulphate solution. A copper plate and a carbon rod are kept in this copper sulphate solution. The copper plate is connected to the positive terminal of a battery whereas the carbon rod is connected to the negative terminal of the battery. What will you observe when an electric current is passed through this set-up for a considerable time?

The process that you saw in Activity 7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

Name all the planets of the Solar System in the order of their increasing distances from the Sun.

Given below are certain food items required for proper nourishment of adolescents. Name the nutrients present in the food items and write their functions.

Food items	Major nutrients	Functions
Pulses and nuts
Oranges and amla
Sugar and roti
Oils
Vegetables