a) What type of mirrors were used?
b) Which energy was put to use for burning?
c) Mention the principle in this process.
d) Draw a ray diagram showing this principle. (4 marks)
A: a) Archimedes used concave mirrors for burning the ships.
b) Solar energy was put to use for burning.
c) Archimedes focused the image of the Sun on the ships by adjusting
the concave mirrors in such a way that their focus lie on the ships.
d) Ray diagram is shown below.
Q: What are your observations about the effects of Oxidation reactions
in daily life. Can you suggest any preventive measures for them? (4
marks)
A: When some metals are exposed to moisture, acids ... etc., they
tarnish due to oxidation. This is called Corrosion.
Tarnishing of silver ware, green coating on copper are some examples for this.
Corrosion causes damage to car bodies, bridges, iron railings, ships
and to all other objects that are made of metals. Corrosion can be
prevented or at least minimised by shielding the metal surface from
oxygen and moisture. It can be prevented by painting, oiling,
greasing, galvanizing, chrome plating or making alloys.
When fats and oils are oxidized they become rancid. Their smell and
taste change. Rancidity is an oxidation reaction. The spoilage of
these food items can be prevented by adding preservatives like Vitamin
C and Vitamin E. Keeping food in air tight containers helps to slow
down oxidation process.
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