# Model Activity Task 1 Physical Science Solution

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1)Determine the unit of ‘R’ from dimensional analysis.
Ans: The dimensions are Mass L² Time^-2 Temp^-1 Mol^-1. where P is the pressure, V is the volume, n is the no of mole, R is gas constant and T is temperature.

2) Mass of 112 mL of a certain gas is 0.22 g at STP. How many molecules are there in the
sample of gas ? What is the molar mass of the gas?
Ans:

3)What are the main reasons for which real gases deviate from ideal behaviour?
Ans: The deviations from the ideal behaviour are considerable at high pressures and low temperatures. Further, it has been found that the most easily liquefiable and highly soluble gases show larger deviations. Thus, gases like carbon dioxide, sulphur dioxide andammonia show much larger deviations than hydrogen, oxygen, nitrogen etc.

4) Why does the sky appear blue during the day ? Where should you place an object with
respect to a convex lens if you intend to use the latter as a magnifying glass?
Ans: There are so many fine particles and in the atmosphere which are smaller than the wavelength of visible light. These are more effective in scattering lightof shorter wavelengths at the blue end of the visible spectrum than at the longer wavelength at the red end. (In fact wavelength of red light is approximately 1.8 times more than that of the blue light). So, blue light is scattered more as compared to red and reaches our eyes. So, the sky appears blue.
Object should be placed at a distance less than focal length order to use a convex lens as a magnifying glass.

5)Why are the elements in group 1 of periodic table called ‘alkali metals’ ? Mention the
symbol of a post-uranium element.
Ans: Group 1 elements form alkaline solutions when they react with water, which is why they are called alkali metals.
Symbol : U

6)From dimensional analysis, derive the unit of ‘M’ in the equation PV=WRT/M
where the symbols have their usual meanings.
Ans:

7)Explain the cause of greenhouse effect?
Ans: Causes of the Greenhouse Effect
1.Burning of Fossil Fuels: Fossil fuels like coal, oil and natural gas have become an integral part of our life.
2.Deforestation: Forests hold a major green area on the planet Earth.
3.Increase in Population: Over the last few decades, there have been huge increase in the population.

8)When white light is incident on a glass slab and emerges after refraction, it does
not form a spectrum. Explain?
Ans: This is because the light has refracted for two times inside the slab and the spectrum which has been formed with first refraction has again converted into white light through the phenomenon of Recombination when it refracted by the second portion.

9)For ionic compounds, why is it reasonable to use the term ‘formula weight’
rather than ‘molecular weight’?
Ans: Molecules are not present in ionic substances. Only ions are present. The formula of an ionic substance represents the simpler ratio of ions in one mole of crystal. Hence a more appropriate term is ‘formula weight’.

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