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Density

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Question 13

A student determines the density of water using two different methods.

Method 1

The student suspends a piece of modelling clay from a forcemeter.

  • The measured weight of the clay in air is W1=1.20 NW_1 = 1.20\text{ N}W1​=1.20 N.
  • The student pours some water into a measuring cylinder and records the initial volume of water as V1=150 cm3V_1 = 150\text{ cm}^3V1​=150 cm3.
  • The clay is then lowered into the water while still suspended from the forcemeter.
  • The new reading on the forcemeter is W2=0.72 NW_2 = 0.72\text{ N}W2​=0.72 N.
  • The new volume reading of the measuring cylinder is V2=198 cm3V_2 = 198\text{ cm}^3V2​=198 cm3.
a.

Explain how the student should read the scale on the measuring cylinder to obtain an accurate value for the volume of water.

[2]
b.

Calculate the density ρ1\rho_1ρ1​ of water from Method 1 using the equation:

ρ1=W1−W2V2−V1×k \rho_1 = \frac{W_1 - W_2}{V_2 - V_1} \times k ρ1​=V2​−V1​W1​−W2​​×k

where k=100 g/Nk = 100\text{ g/N}k=100 g/N. Include the correct unit.

[3]
c.

Method 2

  • The student measures the mass m1m_1m1​ of the measuring cylinder containing the volume V1V_1V1​ of water: m1=282.5 gm_1 = 282.5\text{ g}m1​=282.5 g.
  • The student empties the measuring cylinder as much as possible and measures the mass m2m_2m2​ of the empty cylinder: m2=135.5 gm_2 = 135.5\text{ g}m2​=135.5 g.

Calculate the second value ρ2\rho_2ρ2​ for the density of water using the equation:

ρ2=m1−m2V1 \rho_2 = \frac{m_1 - m_2}{V_1} ρ2​=V1​m1​−m2​​
[2]
d.

Suggest why emptying the cylinder to measure m2m_2m2​ can cause an inaccuracy, and describe an improvement to the procedure in Method 2 to reduce this inaccuracy.

[2]
Markscheme

Density Questions

  1. IGCSE
  2. /Physics
  3. /Density

169 exam-style questions on CIE IGCSE Physics Density, covering Density. Each one has a worked solution and a mark scheme showing where the marks go.

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