Density โ Complete Notes, Revision, Important Questions & Downloads
This topic contains Definition and Properties of Density and Density of Mixed Liquids. NEET tests density through point definition ฯ = dm/dV, unit and dimension questions, the difference between density of a body and density of a substance for hollow objects, and quick numericals on equal-mass or equal-volume mixtures. The OCR also adds two useful corrections: density decreases with temperature rise and increases with pressure rise. That makes this page more than a definition sheet; it is a compact toolkit for later buoyancy and fluid-flow problems.
NEET Weightage - Density
Fluid Mechanics| NEET Year | Questions from this Topic | Bar | Marks |
|---|---|---|---|
| NEET 2024 | 0 | 0 | |
| NEET 2023 | 0 | 0 | |
| NEET 2022 | 0 | 0 | |
| NEET 2021 | 0 | 0 | |
| NEET 2020 | 0 | 0 | |
| NEET 2019 | 0 | 0 | |
| Total (2019-2024) | 0 | ย | 0 |
For a hollow body, density of the body is less than density of the material because the body occupies more volume than the solid substance alone.
Equal-mass mixture density gives the harmonic mean, while equal-volume mixture density gives the arithmetic mean.
Rising temperature usually lowers density by expansion, while higher pressure raises density through compression.
Density Strategy for NEET
Distinguish substance volume from body volume If the object is hollow, the body's total volume exceeds the solid material volume, so the body's density is lower than the material density. This distinction matters in direct statement questions.
Use the right mean for mixed liquids Equal masses lead to the harmonic mean, while equal volumes lead to the arithmetic mean. Mixing these two cases is the fastest way to miss a one-step objective question.
Track what stays constant during temperature or pressure change Mass stays fixed while volume changes, so temperature increase lowers density and pressure increase raises density.
Keep relative density dimensionless Relative density is a ratio to water density, so it carries no unit. This is often checked alongside unit questions on kg/m^3 and g/cc.
Read mixture questions for 'equal masses' or 'equal volumes' first The wording decides the formula immediately, so identify the condition before writing any algebra.
Density Study Materials
PDF ยท Cheat Sheet ยท MCQ Set ยท PYQDensity Subtopics
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Rapid Revision - Density
Concept โ Trap โ Example1) Definition and Properties of Density
Point property and unit systemDensity at a point in a fluid is ฯ = dm/dV. Its SI unit is kg/m^3, CGS unit is g/cc, and relative density is the ratio of body density to water density.
- Density is scalar for homogeneous isotropic substances.
- Density of a hollow body is less than density of the material because the body occupies larger total volume.
- The common trap is to assign a unit to relative density even though it is a pure ratio.
2) Density of Mixed Liquids
Choose the correct meanFor equal masses mixed, the density becomes 2ฯ1ฯ2/(ฯ1 + ฯ2), the harmonic mean. For equal volumes mixed, the density becomes (ฯ1 + ฯ2)/2, the arithmetic mean.
- Immiscible liquids arrange with the highest density at the bottom and the lowest at the top.
- Temperature increase decreases density because volume expands while mass stays fixed.
- Students often use the arithmetic mean in equal-mass problems, which is incorrect.
US Curriculum Gaps - Density
What U.S. Students Usually MissIntro courses often use ฯ = m/V only and skip the point-definition language
NEET sometimes tests the limiting definition dm/dV and expects students to distinguish a local property of a fluid from a rough average over a finite chunk of material.
- Treat density as a point property in fluids.
- Keep the local definition ready even if the numerical problem uses m/V.
Mixture-density rules are rarely packaged as harmonic versus arithmetic mean
The OCR gives these mixture results in a very exam-efficient form. Recognising whether masses or volumes are equal is the actual skill being tested, not the algebra alone.
- Equal masses โ harmonic mean.
- Equal volumes โ arithmetic mean.
Concept IQ Check - Density
4 NEET-style MCQs with AnswersPractice Questions - Density
Click "Reveal Answer" after attempting๐ Reveal Answer
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NEET Physics Revision Checklist
Use this section for quick chapter tracking before mocks, part tests, and final NEET revision.
Density FAQs
Notes ยท Downloads ยท Revision ยท Important QuestionsWhy is density treated as a point property in a fluid?
Why is relative density dimensionless?
Why can a hollow metal ball have lower density than the metal itself?
Why do immiscible liquids arrange themselves by density?
Why does density usually decrease when temperature rises?
Why does density increase with pressure?
Why is the equal-mass mixture formula not the arithmetic mean?
What is the most common mistake in density mixture questions?
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