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Material Science

Density, hardness and conductivity testing

  • 3 things to know
  • AS 5

Overview

Density with worked calculations and unit conversions, measuring the density of irregular samples, the Vickers hardness test with a worked value, and electrical conductivity and resistivity.

What you need to know

Answer each one before you reveal it.

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Key term

State the equation for density and its SI unit.

Key term

A titanium hip stem has a mass of 180 g and a volume of 40.0 cm³. What is its density?

Key term

Describe how the density of an irregularly shaped metal sample is measured.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State the equation for density and its SI unit.

    Model answer

    Density equals mass divided by volume, ρ = m ÷ V. The SI unit is kg m⁻³.

  2. 2

    A titanium hip stem has a mass of 180 g and a volume of 40.0 cm³. What is its density?

    Model answer

    The density is 4.50 g cm⁻³. The working is 180 ÷ 40.0 = 4.50 g cm⁻³.

  3. 3

    Describe how the density of an irregularly shaped metal sample is measured.

    Model answer

    The sample is weighed on a balance to find its mass. The sample is then lowered into water in a measuring cylinder, and the rise in level gives its volume.

  4. 4

    A metal sample of mass 26.7 g raises the water in a measuring cylinder from 50.0 cm³ to 53.0 cm³. What is its density?

    Model answer

    The density is 8.9 g cm⁻³. The volume is 53.0 − 50.0 = 3.0 cm³, and 26.7 ÷ 3.0 = 8.9 g cm⁻³.

  5. 5

    Explain why a density of 1 g cm⁻³ is the same as 1 kg l⁻¹.

    Model answer

    One litre is 1000 cm³, so a litre of a 1 g cm⁻³ substance has a mass of 1000 g. A mass of 1000 g is 1 kg.

  6. 6

    Convert the density of aluminium, 2700 kg m⁻³, into g cm⁻³ and kg l⁻¹.

    Model answer

    The density of aluminium is 2.70 g cm⁻³, which is also 2.70 kg l⁻¹. The working is 2700 ÷ 1000 = 2.70, since 1 g cm⁻³ equals 1000 kg m⁻³.

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