Density of Solid (Denser than Water) MCQs Quiz | Class 9

This Class IX Science (Code 086) Practicals (Unit III) quiz focuses on determining the Density of a Solid (Denser than Water). It covers key concepts including the spring balance and measuring cylinder method, least count calculations, and the calculation approach for mass and volume. Attempt all 10 questions to test your understanding, then submit to view your detailed scorecard and download the answer key PDF.

Understanding Density of Solids (Practicals)

Density is a fundamental physical property defined as mass per unit volume. In the Class 9 science practical syllabus, students learn to determine the density of a solid that is denser than water (does not float) using simple laboratory equipment.

The Method

The experiment involves two main measurements:

  • Mass (M): Measured using a Spring Balance. The solid is suspended from the hook, and the reading is noted in grams (g) or kilograms (kg).
  • Volume (V): Measured using a Measuring Cylinder containing water. The solid is immersed completely, and the rise in water level indicates the volume of the solid (Archimedes’ Principle logic regarding displacement).

Formula

Density (D) = Mass (M) / Volume (V)

The SI unit of density is kg/m3 (kilogram per cubic meter), though g/cm3 (gram per cubic centimeter) is commonly used in laboratories. To convert g/cm3 to kg/m3, multiply by 1000.

Step-by-Step Procedure

  1. Note the Zero Error and Least Count of the spring balance and measuring cylinder.
  2. Tie the solid with a thin strong thread.
  3. Measure the weight of the solid in air using the spring balance. Let this be M.
  4. Pour water into a measuring cylinder and note the initial level (V1).
  5. Lower the solid gently into the water until it is fully submerged. Ensure it does not touch the bottom or sides.
  6. Note the final water level (V2).
  7. Calculate Volume V = V2 – V1.
  8. Calculate Density = M / V.

Important Precautions

  • Parallax Error: Always read the lower meniscus of the water level at eye level.
  • Dryness: The solid should be dry when measuring its mass in air.
  • Immersion: The solid must be completely submerged but should not touch the glass walls.
  • Bubbles: Ensure no air bubbles stick to the solid when submerged, as they increase the apparent volume.

Quick Revision Notes

  • Least Count: The smallest value an instrument can measure. Calculated as (Range / Number of Divisions).
  • Zero Error: If the pointer is not at zero initially, the error must be subtracted from the final reading.
  • Thread: Use a very thin thread so its volume is negligible.

Extra Practice Questions

1. If a solid has a mass of 50g and displaces 10ml of water, what is its density? (Ans: 5 g/cm3)
2. Why is a measuring cylinder preferred over a beaker? (Ans: Higher accuracy/finer graduations)
3. What happens to the water level if the solid touches the bottom? (Ans: No change in level, but risk of breakage/incorrect suspension)
4. If the pointer of a spring balance is above zero mark, is the error positive or negative? (Ans: Negative error)
5. Can this method be used for sugar crystals? (Ans: No, sugar dissolves in water)