Practical Skills QWC practice question
Question
Describe how you would accurately determine the density of a small, irregularly shaped stone using standard laboratory equipment.
Your answer should explain which measurements you would take, the equipment you would use, and how you would reduce the uncertainty in your result.
Student guidance
Write in clear, linked sentences using correct physics terms.
Expected physics points
- Measure the mass of the stone using a calibrated electronic balance.
- Measure the volume by displacement: lower the stone into water in a measuring cylinder (or eureka can) and record the volume of water displaced.
- Calculate density using ρ = m/V.
- Reduce uncertainty: choose instruments with appropriate resolution for the size of the stone.
- Read the measuring cylinder at eye level to avoid parallax, reading the bottom of the meniscus.
- Repeat measurements and take a mean; use a larger stone so percentage uncertainties are smaller.
Mark scheme points
- Measure the mass of the stone using a calibrated electronic balance.
- Measure the volume by displacement: lower the stone into water in a measuring cylinder (or eureka can) and record the volume of water displaced.
- Calculate density using ρ = m/V.
- Reduce uncertainty: choose instruments with appropriate resolution for the size of the stone.
- Read the measuring cylinder at eye level to avoid parallax, reading the bottom of the meniscus.
- Repeat measurements and take a mean; use a larger stone so percentage uncertainties are smaller.
Indicative content
- Measure the mass of the stone using a calibrated electronic balance.
- Measure the volume by displacement: lower the stone into water in a measuring cylinder (or eureka can) and record the volume of water displaced.
- Calculate density using ρ = m/V.
- Reduce uncertainty: choose instruments with appropriate resolution for the size of the stone.
- Read the measuring cylinder at eye level to avoid parallax, reading the bottom of the meniscus.
- Repeat measurements and take a mean; use a larger stone so percentage uncertainties are smaller.
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