DIFFERENCES FROM PAST PAPERS (1996)

1. Thermoplastics & Thermosetting Plastics

Thermoplastics
i) Plastics that can be melted again and again are known as thermoplastics.
ii) They behave just like wax.
iii) These plastics can be shaped again and again.
iv) Examples: Nylon, PVC, Teflon etc.

Thermosetting Plastics:
i) Plastics that can be melted only once are known as thermosetting plastics.
ii) They become hard after melting.
iii) These plastics cannot be shaped again and again.
iv) Examples: Polyesters and Bakelite.

2. Lunar & Solar Eclipse

Lunar Eclipse
i) It occurs when the earth comes between moon and sun.
ii) Moon goes through series of partial eclipses when moon comes out of umbral region of earth’s shadow.
iii) Earth lies in umbral region at total eclipse when earth lies exactly between moon and sun and its shadow covers the whole moon.

Solar Eclipse
i) It occurs when moon comes between earth and sun.
ii) Partial eclipse of sun occurs as in Penumbra can see a part of the sun.
iii) At the total eclipse of the sun, the shadow of moon which it throws on earth consists of an umbra and penumbra people on earth who are in umbral region cannot see the sun.

3. Asteroid & Meteorite

Asteroid:
i) The small rocky objects which are orbiting the sun between orbits of Mars and Jupiter are known as asteroids.
ii) Its origin is concentrated to the remains of planets that fell apart.
iii) Asteroid means star like but these are known as minor planets.

Meteorite:
i) Tiny chunk of material floating in space, which can also enter the earth’s atmosphere and become meteor are known as meteorites.
ii) It may originate by the disintegration of comet.
iii) A falling star (Meteor) is seen as a streak of light in sky.

4. Renewable & Non-renewable resources

Renewable Resources
i) Renewable resources are used continuously and can be used again and again.
ii) Major examples are: air, water, soil, wildlife, forests, fish etc.
iii) These resources support millions of people all over the world.
iv) Renewable resources are constantly renewed by bio-geochemical cycles of nature.

Non-renewable Resources
i) Non-renewable resources cannot be used again and again after their consumption.
ii) Major examples include: Coal, oil, natural gas etc.
iii) These resources cannot support millions of people all over the world.
iv) Non-renewable resources are being exhausted day by day because their demand rises. Due to worldwide demand of fossil fuels, its supplies are declining.
OR
Renewable resources-
1) the resources that can be renewed by reproduction are called renewable resources.
2) Renewable resources are inexhaustible.
3) Renewable resources are not affected by the human activities.
4) All biotic resources are renewable.
5) For example: air and water.

Non-renewable resources-
1) the resources that are present in fixed quantities are called non-renewable resources.
2) Non-renewable resources are inexhaustible.
3) Non-renewable resources are affected by human activities.
4) Some abiotic resources are non-renewable.
5) For example- fossil fuels and minerals.

5. Endothermic & Exothermic Reaction

Exothermic Reaction
i) Energy is drawn in from the external environment, causing its surroundings to loose heat, or "cool down."
ii) The endothermic chemical reaction creates a product that has a higher energy level than the original materials, causing the reactant's stored energy to decrease. (In scientific terms, the reactants have "less total enthalpy" than the product.)
iii) The resulting product of the reaction is less stable because, the higher the energy bond, the less strength its molecules possess.
iv) Most endothermic reactions are not spontaneous.
v) Example: Melting ice. In order for ice to melt, it needs to draw in the heat (energy) from its surroundings. The ice becomes less stable as it responds to the increased heat. The ice stored energy decreases. The end product is water, which has a higher energy level than the ice.

Exothermic Reactions
i) Exothermic chemical reactions cause their surroundings to warm up by giving off heat.
ii) The reactants contain more stored energy than the product because energy from external sources is not required, but given off. This gives the product more stability due to the lower amount of energy needed. (In this case, the reactants have a "greater total enthalpy" than the product.)
iii) Exothermic reactions are usually spontaneous.
iv) Example lighting a match. When the head of the match is struck, it results in the spontaneous release of stored energy (heat) from the reactants into the surroundings. The flame that is produced has a lower level of energy than the match and the striking surface because the reaction is giving off stored energy and not required to draw energy in from its surroundings.

6. Star & Planet

Star
i) Stars are self-luminous heavenly bodies.
ii) They do not revolve around the sun.
iii) They are usually stationary.
iv) Examples: fixed stars, binary stars.

Planet:
i) Planets are rocky non-luminous bodies.
ii) They revolve round the sun.
iii) They usually move.
iv) Examples: Mercury, Venus, Jupiter etc.

7. Nuclear Fission & Fusion

Fission:
i) Lighter atoms are fused together at a very high temperature to form heavier elements.
ii) It is difficult to carry out on the earth.
iii) It has no nuclear waste problem.
iv) It requires cheaper and abundant elements.
v) Not possible at concerning scale as high temperature is needed to start it.

Fusion:
i) Heavier unstable atoms are broken down to produce energy.
ii) It is easy to carry out on the earth.
iii) It has nuclear waste radioactivity disposal problem.
iv) It requires expensive and rare elements.
v) Possible to commercialize under controlled measure.