You are here
Download the questions here
The password to open the file is - teachooisbest
Q1. Give the full form of LPG and CNG
Answer
- LPG stands for Liquified Petroleum Gas and
- CNG stands for Compressed Natural Gas.
Q2. Why is the diffusion of one solid into another a slow process? What could be an example of diffusion of one solid in another. Give examples for the same.
Answer
Particles in solids are packed tightly and the particles do not move from their position. They only vibrate from their own position. This makes it difficult for one solid to diffuse into another and thus the process is slow.
Alloys of metals are the best example for diffusion of a solid in another solid.
Example :
- Brass is an alloy of Copper and Zinc
- Bronze is an alloy of copper and tin
- Nichrome is an alloy Nickel and Chromium
Q3. Why is air used to inflate tyres?
Answer
Air has the property of high compressibility under some extent of pressure. Air also has pressure and makes it easy to drive smoothly on roads.
Q4. Why is steel used while laying railway lines?
Answer
Steel is an alloy and has greater strength. This property makes the railway lines stronger when made of steel.
Moreover, steel expands during the summer months but the expansion only results in increase in size and no change in shape.
Q5. Honey is more viscous than water. Give reason
Answer
Viscosity is a measure of a fluid's resistance to flow . Particles of matter have a certain force of attraction between them. This force of attraction between particles of honey is more than that in water . This makes honey more viscous than water.
Q6. Explain ‘Osmosis is a special kind of Diffusion’. State if the following example is osmosis or diffusion:
- Swelling up of raisins while keeping in water
- Spreading of virus on sneezing
- Earthworm dying on coming into contact with air
- Shrinking of grapes when kept in sugar syrup
- Preserving of pickles in salt
- Smell of food being cooked
- Aquatic animals using dissolved oxygen in water to breathe
Answer
Diffusion is the movement of particles from a region of high concentration to low concentration without the presence of a membrane . It can be the movement of solute as well as solvent molecules.
Osmosis is the movement of particles from a region of high concentration to low concentration across a semipermeable membrane . Thus Osmosis is a special kind of Diffusion.
Only the solvent molecules can pass through.
- Swelling up of raisins while keeping in water - Osmosis
- Spreading of virus on sneezing - Diffusion
- Earthworm dying on coming into contact with air - Osmosis
- Shrinking of grapes when kept in sugar syrup - Osmosis
- Preserving of pickles in salt - Osmosis
- Smell of food being cooked - Diffusion
- Aquatic animals using dissolved oxygen in water to breathe - Diffusion
Q7. What is Brownian Motion? What causes the zig-zag motion of pollen grains when added to a glass of water?
Answer
The random motion of larger visible particles due to the motion of the smaller invisible particles of matter is known as Brownian motion .
Though the water molecules are very small and invisible to naked eyes, their presence and movement are visible through the movement of the visible larger pollen grains. The water molecules that move at a fast pace strike against the pollen grains resulting in the zig-zag motion of pollen grains.
Q8. Which one of the following sets of phenomena would increase on raising the temperature?
(a) Diffusion, evaporation, compression of gases
(b) Evaporation, compression of gases, solubility
(c) Evaporation, diffusion, expansion of gases
(d) Evaporation, solubility, diffusion, compression of gases
Answer
(c) Evaporation, diffusion, expansion of gases
Reason : As the temperature increases, the kinetic energy of the particles increases.
- Evaporation : As the kinetic energy increases the particles can break free from the rest of the liquids with greater ease.
- Diffusion : With the increase in kinetic energy, the particles of one matter can diffuse into another easily.
- Expansion of gases : With the increase in temperature, gases expand
Q9. Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions.
(a) Low temperature, low pressure
(b) High temperature, low pressure
(c) Low temperature, high pressure
(d) High temperature, high pressure
Answer
(c) Low temperature, high pressure
Reason : Under conditions of low temperature and high pressure, the particles of the gas come closer to each other. This enables us to liquefy gases.
Q10. ln which of the following conditions, the distance between the molecules of hydrogen gas would increase?
(i) Increasing pressure on hydrogen contained in a closed container.
(ii) Some hydrogen gas leaking out of the container.
(iii) Increasing the volume of the container of hydrogen gas.
(iv) Adding more hydrogen gas to the container without increasing the volume of the container.
(a) (i) and (iii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii)and(iv)
Answer
(c) (ii) and (iii)
Explanation : (ii) When some Hydrogen gas leaks out of the container, the remaining gas spreads out to occupy the entire space. When a lesser amount of gas occupies the same space, the space between the particles increases.
(iii) When the volume of the container is increased the same amount of gas has a larger amount of space to occupy . So the gas spreads out to fill the whole space. Thus the space between the molecules increases.
Q11. A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.
Answer
Pure water boils at 100 °C. The sample of water boils at 102°C at normal temperature and pressure. Since it boils at a temperature higher than pure water, the sample of water is not pure.
Also, the water will not freeze at 0°C because it is impure. It will freeze at a temperature below 0°C.
Q12. A student heats a beaker containing ice and water. He measures the temperature of the content of the beaker as a function of time.
Which of the following graphs would correctly represent the result? Justify your choice.
Answer
(d) Initially ice and water are at equilibrium, so the temperature is 0°C. On heating ice, the heat energy is used in complete conversion of ice to water. This is called the latent heat of fusion. At this point, there is no increase in temperature. Once all the ice is melted, the temperature slowly rises. Thus graph (d) is correct.
Q13. Match the physical quantities given in column A to their SI units given in column B.
|
Column A |
Column B |
|
a. Pressure |
i. Cubic meter |
|
b. Temperature |
ii. Kilogram |
|
c. Density |
iii. Pascal |
|
d. Mass |
iv. Kelvin |
|
e. Volume |
v. Kilogram per cubic meter |
Answer
- → iii
- → iv
- → v
- → ii
- → i
Q14. Water as ice has a cooling effect, whereas water as steam may cause severe burns. Explain these observations.
Answer
Ice and Steam are both forms of water. Ice is formed by freezing water at lower temperatures. The energy in ice is low. When we touch ice, the heat from our body is transferred to the ice and heat is transferred from regions of higher temperature to that of lower temperature. Since there is reduction of heat in our body, there is a cooling effect.
Steam on the other hand is formed when water is heated at boiling point and converts to vapours. The vapours possess very high energy. The high energy of steam in terms of heat causes severe burns when we touch.
Q15. Look at the figure and suggest in which of the vessels A, B, C or D the rate of evaporation will be highest? Explain.
Answer
Figure C shows the highest rate of evaporation.
Explanation:
Rate of evaporation increases with an increase in surface area. Also, the rate of evaporation increases with an increase in wind speed. In figure C, the surface area exposed is high and The fan increases the wind speed.
On comparing A and D, though the surface area in A is high, the wind speed is relatively less in A. B has less surface area exposed to the open, so the rate of evaporation is less. D is not exposed for evaporation.
