Loss in Weight vs Displaced Water (Tap Water) MCQs Quiz | Class 9

This interactive quiz for Class IX Science (Code 086) covers Unit III: Practicals. Specifically designed for the topic “Loss in Weight vs Displaced Water,” it tests your understanding of immersion, buoyancy relations, and observation tables using two different solids. Complete the 10 MCQs below, check your score, and download the result PDF for your records.

Study Notes: Establishing the Relationship

This experiment aims to verify Archimedes’ Principle by establishing the relationship between the loss in weight of a solid when fully immersed in tap water and the weight of the water displaced by it.

1. Key Concepts

  • Buoyancy: The upward force exerted by a fluid on an immersed object. Also known as Upthrust.
  • Archimedes’ Principle: When a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it.
  • Apparent Weight: The weight of the object inside the water, which is less than its real weight in air.

2. Formulas and Relationships

The core observation relies on the following equality:

Loss in Weight = Weight of Displaced Water

Mathematically:

  • Let W1 be the weight of the solid in air.
  • Let W2 be the weight of the solid in tap water.
  • Loss in Weight = W1 – W2.
  • If the displaced water is collected and weighed (W3), then (W1 – W2) should be approximately equal to W3.

3. Experimental Setup & Precautions

  • Overflow Can: Used to collect displaced water accurately. It must be filled exactly up to the spout before immersion.
  • Spring Balance: Used to measure the weight of the solid. Zero error must be checked before use.
  • Immersion: The solid must be completely immersed in water but should not touch the bottom or sides of the container.
  • Thread: A thin, strong thread with negligible mass and volume should be used to suspend the solid.

4. Reading the Meniscus

When measuring the volume of displaced water in a measuring cylinder, always read the lower meniscus of the water level to avoid parallax error.

5. Extra Practice Questions

  • Q: Why does a heavy ship float?
    A: Because the weight of the water it displaces is equal to the total weight of the ship (Law of Flotation).
  • Q: Does the shape of the solid affect the upthrust?
    A: No, only the volume of the immersed part affects the volume of displaced fluid.
  • Q: How does salty water affect the loss in weight compared to tap water?
    A: Salty water is denser, so it exerts more upthrust, causing a greater loss in weight.
  • Q: What is the SI unit of Upthrust?
    A: Newton (N).
  • Q: If a solid floats, what is its apparent weight?
    A: Zero.