1.4 Density Experiments
Master the three essential methods for measuring density in the IGCSE laboratory
The Hook: Why Density Matters
Ships made of steel float, yet a steel marble sinks. Helium balloons rise while air-filled ones fall. Oil floats on water in your salad dressing. All these phenomena are explained by one property: density.
Density determines whether objects sink or float, whether hot air rises, and even why icebergs are dangerous (90% underwater!). In IGCSE Physics, you must know how to measure density for three different scenarios.
Core Concept: The Density Formula
ρ = m / V
Mark Scheme Keywords:
- • Density is the mass per unit volume
- • The SI unit is kg/m³ (also accept g/cm³ for small objects)
- • Conversion: 1 g/cm³ = 1000 kg/m³
Paper 6: The Three Methods
Method 1: Regular Solids (Cuboid, Cylinder, Sphere)
Procedure:
- 1. Measure mass using a digital balance (record in grams)
- 2. Measure dimensions using a ruler or vernier caliper:
- • Cuboid: length (l), width (w), height (h)
- • Cylinder: diameter (d) and height (h)
- • Sphere: diameter (d)
- 3. Calculate volume using the appropriate formula
- 4. Calculate density: ρ = m / V
Interactive Cuboid Density Calculator
⚠️ Examiner Trap:
Always measure each dimension at least 3 times and calculate the average. Measure at different positions to account for irregularities.
Common Mistakes:
- • Unit mismatch: Using cm for one dimension and mm for another
- • Wrong formula: V = l + w + h (WRONG! It's l × w × h)
- • Single measurement: Not taking repeat readings reduces accuracy
Paper 6 Errors & Improvements
Random Errors
- • Reading variation: Different meniscus readings each time
- • Balance fluctuation: Digital balance shows slightly different values
- • Temperature changes: Room temperature affects liquid volume
Solution:
Take repeat readings (minimum 3) and calculate the average
Systematic Errors
- • Zero error: Balance doesn't read 0.00 g when empty
- • Air bubbles: Consistent presence of trapped air
- • Wrong formula: Using V = l + w + h instead of l × w × h
Solution:
Zero the balance before use. Check for air bubbles. Verify calculations.
Mark Scheme Keywords for Improvements:
- • "Use a more precise instrument (e.g., vernier caliper instead of ruler)"
- • "Take repeat readings and calculate the mean"
- • "Ensure the object is fully submerged without touching the sides"
- • "Read at eye level to avoid parallax error"
- • "Zero the balance before taking measurements"
Syllabus Checklist (Extended)
Exam Success Formula
Paper 6 Questions = Method + Safety + Errors + Improvements. Always state:
- The apparatus used (measuring cylinder, balance, vernier caliper)
- The procedure in numbered steps
- How to reduce errors (repeat readings, avoid parallax, zero the balance)
- The calculation with units
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