Q. How do you appreciate the role of the higher specific heat of water in stabilizing atmospheric temperature during winter and summer seasons?
A: Everyday earth receives a large amount of solar energy. The oceans on the earth absorb much of this energy for maintaining a
relatively constant temperature in the atmosphere.
1. Infact the oceans work like heat store houses for the earth.
2. These oceans absorb large amounts of heat at the equator without raise in temperature due to high specific heat of water.
3. So oceans moderate the surrounding temperature near the equator.
4. Ocean water also transports the heat away from the equator to the Polar regions.
5. This transportation helps in moderate the temperature or climates in the areas that are far from the equator.
6. Thus water in the oceans can stabilize the temparature on earth in winter and summer seasons.
Q. Discuss the merits and demerits of using mirrors in building elevation.
A: Merits : Glass can be prepared into different shapes and sizes.
1. Glass used in the elevated buildings can be colourless or may be coloured. Building becomes attractive.
2. Glass does not rust in moist air.
3. Glass does not let water to pass through it.
Demerits:
1. Glass is a very expensive material and it is cost effective.
2. Glass is brittle in nature and thus it breaks
easily.
3. Glass can melt under very high temperatures.
4. It changes the passing by drivers concentration.
5. Birds like sparrows, crows etc get confused while flying across these buildings.
6. The mirrors elevation in buildings is not eco friendly.
Q. Why does tooth decay start when pH of mouth is lower than 5.5?
A: Tooth decay starts when the pH of the mouth is lower than 5.5.
1. Tooth enamel made of calcium phosphate is the hardest substance in the body.
2. It does not dissolve in water, but is corroded when the pH is below 5.5.
3. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth.
Preventions:
1. The best way to prevent this is to clean the mouth after eating the food.
2. Using tooth pastes which are generally basic neutralize the excess acid and prevent tooth decay.
Practice Questions:
1. a) What is oxidation reaction? Give an example.
b) What is reduction reaction? Give an example.
c) Taking copper oxide as sample describe an activity to explain the process of reduction.
2. Suppose 1 L of water is heated for a certain time to rise its temparature by 2 °C of 2 L of water is heated for the same time, by how much will its temparature rise?
3. The radius of curvature of a concave mirror is 30 cm. What is its focal length?
4. What happens when silver bromide is placed in sunlight for sometime?
5. Write a list of the objects which act as a concave or convex mirror in your sourroundings
6. What happens when silver bromide is placed in sunlight for sometime?