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**LESSON DEVELOPMENT**

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    LESSON OF A DAY

     **054-032-1-4.2 RELATIVE DENSITY OR SPECIFIC GRAVITY**
    FORM I, PHYSICS LESSON - DENSITY AND RELATIVE DENSITY.

    LESSON VIDEO

    LESSON NOTES
    **054-032-1-4.2 RELATIVE DENSITY OR SPECIFIC GRAVITY**
    LESSON 4.2: RELATIVE DENSITY (SPECIFIC GRAVITY)
    Introduction
    • Definition: Relative density is a way to compare how heavy a substance is compared to water.
    • Formula:
    • Relative Density = Density of substance ÷ Density of Water
    Notes:
    o The density of water is taken at 4°C (when water is densest).
    o Relative density is unitless (no units).
    • Example:
    o Density of substance = 2 g/cm³
    o Density of water = 1 g/cm³
    R.D.= 2 /
    1.
    RD =
    2.
    The substance is twice as dense as water.
    • Observation:
    o If R.D. < 1 → substance floats on water
    o If R.D. > 1 → substance sinks in water
    Relative Density of Liquids
    • Definition: Relative density of a liquid is the ratio of the density of the liquid to the density of water.
    • Purpose: Tells us how heavy a liquid is compared to water.
    Method 1: Using a Relative Density Bottle (Density Bottle)
    • Apparatus:
    o Relative density bottle
    o Balance
    o Water
    o Test liquid
    o Dry cloth/tissue
    Procedure:
    1. Measure the mass of the empty bottle → M1
    2. Fill the bottle with water, wipe dry, weigh → M2
    3. Fill the bottle with test liquid, wipe dry, weigh → M3

    Calculations:
    Mass of water = M2 − M1
    Mass of liquid = M3 − M1
    Relative Density = (M3 − M1) ÷ (M2 − M1)
    Conclusion: The bottle holds equal volumes, so comparing masses gives the relative density.
    Method 2: Using a Hydrometer
    • Description: A hydrometer floats in liquids and measures relative density directly.
    Procedure:
    1. Pour liquid into a tall container.
    2. Gently place the hydrometer and let it float freely.
    3. Read the scale at the liquid surface.
    Explanation:
    • Hydrometer sinks more in lighter liquids.
    • Hydrometer floats higher in denser liquids.

    Method 3: Using Measuring Cylinder and Balance
    • Procedure:
    1. Measure a fixed volume of water in a measuring cylinder and find its mass.
    2. Measure the same volume of test liquid and find its mass.
    Formula:
    Relative Density = Mass of liquid ÷ Mass of equal volume of water

    Precautions in the Laboratory
    • Ensure the bottle is clean and dry.
    • Avoid air bubbles when filling liquids.
    • Use the same volume for water and test liquid.
    • Read measurements carefully.
    Summary
    • Relative density compares the heaviness of a substance to water.
    • Methods to find relative density of liquids:
    1. Using a relative density bottle
    2. Using a hydrometer
    3. Comparing equal volumes of liquid and water
    Relative density helps us compare liquids and understand how they behave in fluids.




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