Don Bosco Academy Class 8 Physics | First Unit Test | 10-Jul-24

Don Bosco Academy

First Unit Test 2024-25

Class 8 Physics  | Full Marks: 20  | Time: 1 hr | Date: 10-Jul-24


I. Select the correct alternative: (5q x 1m = 5m)

1. Which of the following substances undergo sublimation?

  • sodium chloride
  • ammonium chloride
  • sugar
  • sand
2. What is the correct term for the phase change from gas to solid directly?
  • sublimation
  • fusion
  • vaporization
  • deposition
3. An object, which does not float on water:
  • ship
  • boat
  • iron nail
  • wooden ball
4. Which of these is a physical quantity?
  • solid
  • liquid
  • density
  • gas
5. SI unit of density is:
  • grams per cubic centimeter
  • kg per cubic meter
  • grams per cm
  • kg per meter
II. The density of gold is 19.3 grams per cubic centimeter. What is the mass of a bar of gold in kilogram that measures6 cm x 4 cm x 2 cm? (2 m)

III. Explain why gases do not have a definite shape or a definite volume. (2 m)

IV. Give two points of distinction between solids, liquids and gases. (2 m)

V. A piece of plastic has a mass of 150 grams and occupies a volume of 330 cubic cm. Find the density of wood in: (3 m)
  1. CGS System
  2. SI System
VI. Mention the change of state in the following processes: (3 m)
  1. drying of clothes
  2. dewdrops on leaves
  3. dry ice turns into gas
VII. Define the following terms: (3 m)
  1. Archimedes Principle
  2. The Plimsoll line
Answers:

I. 1-b, 2-a, 3-c, 4-c, 5-b 

II. Density = Mass / Volume
=> 19.3    = Mass / (6 x 4 x 2)
=> Mass  = 19.3 x 48
                = 926.4 gram
                = 0.9264 kg

III. Gases do not have definite shape or volume because of their weak intermolecular forces of attraction and the large spaces between their molecules.

IV. Two points of distinction between solids, liquids and gases are as follows:
  • Solids have the highest,  liquids have less and gases have the least intermolecular forces of attraction.
  • Solids have no intermolecular space, Liquids have some, whereas gases have the maximum intermolecular space.

V. 1) Density = Mass / Volume
                     = 150 / 330
                     = 0.45 gram per cubuc cm
    2) Density  = Mass / Volume
                     = 150 / 330
                     = 0.45 gram per cubic cm
                     = 0.45* (1/1000 kg) / {(1/1000000 cubic m)
                     = 450 kg per cubic m

VI. The change of state are:
        1. In the drying of clothes, liquid changes into gas by evaporation
             Liquid ----------> Gas

        2. During dewdropformation on leaves, water vapour (gas) condenses to liquid on cooling
             Gas ----------> Liquid

        3. Solid dry ice turns into gas on sublimation
             Solid----------> Gas

VII. 
  1. Archimedes Principle states that an object immersed in a liquid, fully or partially, experiences an upward buyont force, called upthrust, that is equal in magnitude to the force of gravity on that liquid.
  2. The Plimsoll line is a reference mark located on the hull of a ship, that indicates the maximum depth to which the ship may be safely immersed when loaded with cargo.

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