Cambridge International AS & A Level · P3 · structured
Read, correct and justify
AS practical 2: instrument stations and defensible uncertainty · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 17
- Topics
- 4
- Answer
- Complete
Use only these constructed raw station observations. Force meter: four equal intervals lie between the labelled 1.0 N and 2.0 N marks, and the pointer is at the second interval above 1.0 N. Micrometer: sleeve 3.5 mm, thimble mark 28 on a 0.01 mm-per-division scale, and a closed-jaw zero reading of +0.02 mm. Millimetre ruler: the two object ends read 12.4 cm and 18.7 cm; both ends are sharp, stationary and viewed normally, and for this initial resolution-based estimate assume no additional calibration or positioning error. A digital balance displays 23.4 g and changes in 0.1 g steps. (a) Find the force-meter division value and force. (b) Correct the micrometer reading. (c) Calculate the ruler length; choose and justify an initial uncertainty for each end from the scale division, combine the two conservatively and express the length uncertainty as a percentage. State one reason a real experiment might need a larger uncertainty. (d) Choose an instrument and explain an operating detail for angle, mass, water volume, temperature, current and potential difference, and external diameter. State the digital balance resolution and explain why it does not establish the measurement's complete uncertainty. These are constructed descriptions, not observed experimental evidence.
- (a)
Find the force-meter scale interval and force.
2 marks - (b)
Read and zero-correct the micrometer.
2 marks - (c)
Estimate and justify the ruler uncertainty from the stated measuring process; calculate length and percentage uncertainty.
5 marks - (d)
Select and explain the six other measurement procedures; interpret digital resolution.
8 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
Find the force-meter scale interval and force.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
(a) Division=(2.0-1.0)/4=0.25 N and force=1.0+2(0.25)=1.50 N: 2 marks.
(b)
Read and zero-correct the micrometer.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
(b) Diameter=3.5+28(0.01)-0.02=3.76 mm: 2 marks for combining the scales and applying the zero correction.
(c)
Estimate and justify the ruler uncertainty from the stated measuring process; calculate length and percentage uncertainty.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
(c) Length=18.7-12.4=6.3 cm: 1 mark. Half a 1 mm division is an initially justified ±0.5 mm=±0.05 cm per end under the stated sharp, stationary, normal-viewing assumptions: 1 mark. Two uncertain end readings give a conservative absolute uncertainty 0.05+0.05=0.10 cm: 1 mark. Percentage=100(0.10/6.3)=1.59%, about 1.6%: 1 mark. Identify a real reading-process limitation such as residual parallax, poorly defined ends or calibration that may require a larger uncertainty: 1 mark. A consistently justified larger initial estimate may be accepted, but bare substitution of an unexplained uncertainty is insufficient.
(d)
Select and explain the six other measurement procedures; interpret digital resolution.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
(d) Award 1 mark each for six explained instrument/operation choices: centre and align a protractor; level/tare and stabilise a balance; read a level cylinder at the water meniscus; immerse and stabilise a thermometer; ammeter in series and voltmeter in parallel with correct sockets/ranges; caliper outside jaws square to the diameter with zero check. Award 1 mark for 0.1 g digital resolution and 1 for distinguishing it from calibration/fluctuation uncertainty: 8 marks.
Complete marking guidance
Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.
- (a) Division=(2.0-1.0)/4=0.25 N and force=1.0+2(0.25)=1.50 N: 2 marks.
- (b) Diameter=3.5+28(0.01)-0.02=3.76 mm: 2 marks for combining the scales and applying the zero correction.
- (c) Length=18.7-12.4=6.3 cm: 1 mark. Half a 1 mm division is an initially justified ±0.5 mm=±0.05 cm per end under the stated sharp, stationary, normal-viewing assumptions: 1 mark. Two uncertain end readings give a conservative absolute uncertainty 0.05+0.05=0.10 cm: 1 mark. Percentage=100(0.10/6.3)=1.59%, about 1.6%: 1 mark. Identify a real reading-process limitation such as residual parallax, poorly defined ends or calibration that may require a larger uncertainty: 1 mark. A consistently justified larger initial estimate may be accepted, but bare substitution of an unexplained uncertainty is insufficient.
- (d) Award 1 mark each for six explained instrument/operation choices: centre and align a protractor; level/tare and stabilise a balance; read a level cylinder at the water meniscus; immerse and stabilise a thermometer; ammeter in series and voltmeter in parallel with correct sockets/ranges; caliper outside jaws square to the diameter with zero check. Award 1 mark for 0.1 g digital resolution and 1 for distinguishing it from calibration/fluctuation uncertainty: 8 marks.
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