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Fundamental data analysis

From Paper 1: Fundamentals of physics
32(c)4 marks
A temperature sensor is a thermistor in series with a fixed 2.2 kΩ resistor across 5.0 V. The output is across the fixed resistor. The thermistor's resistance is 4.7 kΩ at 20 °C and 2.2 kΩ at 40 °C. Calculate the output at each temperature and the mean sensitivity.

Advance Notice article (written for this paper): Seeing inside the body with antimatter

(1) Positron emission tomography (PET) builds a three-dimensional map of where a radioactive tracer collects in the body. The most common tracer is a sugar labelled with fluorine-18, which decays by β⁺ emission with a half-life of 110 minutes. (2) Because fluorine-18 decays so quickly, it is made in a cyclotron close to the hospital. A typical dose leaves the cyclotron at 08:00 with an activity of 2.0 GBq and is injected about two hours later. (3) Each positron travels about a millimetre through tissue before it meets an electron. The pair annihilates, producing two gamma photons, each of energy 511 keV, which travel in almost exactly opposite directions. (4) A ring of detectors surrounds the patient. When two detectors on opposite sides register photons within a few nanoseconds of each other, the annihilation must have happened somewhere on the line joining them. Modern scanners also measure the tiny difference in arrival times to locate the event along that line. (5) A scan typically collects about 4 × 10⁸ such coincidences in 20 minutes. Like all counting experiments, the image is noisy: the uncertainty in N counts is about √N. (6) A PET scan gives the patient an effective dose of about 7 mSv, compared with an average background dose in the UK of 2.7 mSv per year. The commonly used risk estimate is a 5% chance of a fatal cancer per sievert. (7) PET shows what tissues are doing (for example, fast-growing tumours take up more sugar), while X-ray CT shows their structure. Many scanners combine the two.
From Paper 2: Scientific literacy in physics
8(h)6 marks
Paragraph 5 says the uncertainty in N counts is about √N. (i) Calculate the percentage uncertainty for a region recording 2500 counts. (ii) How long would the scan need to be to halve this uncertainty? (iii) Explain why doubling the injected activity is not a good alternative.
From Paper 3: Practical skills in physics
1(b)5 marks
Results:
λ / nm470525590625660
V / V2.6452.3682.1071.9891.884
Figure 1 shows V against 1/λ. Use it to determine the Planck constant.
1.41.61.822.21.622.42.8(1/λ) / 10⁶ m⁻¹V / Vdatabest fit
Figure 1
From Paper 3: Practical skills in physics
1(c)4 marks
Evaluate the method, identifying the largest source of uncertainty and its likely effect on the result.
From Paper 3: Practical skills in physics
2(b)5 marks
Results:
T / K283298313328343
R / Ω18 63610 000569634162142
The model is R = R₀e^(B/T). Show that the data fit the model and find B.
From Paper 3: Practical skills in physics
3(c)4 marks
Repeated halving times were 3.2, 3.3, 3.4 and 3.3 s. Estimate the uncertainty in C.
From Paper 3: Practical skills in physics
4(b)5 marks
Results:
f / Hz256320384426512
L / m0.3230.2570.2120.1910.157
The model is L = v/(4f) − e, where e is the end correction. Use a suitable graph to find v and e.
From Paper 3: Practical skills in physics
5(b)6 marks
For one card, the amplitude fell from 100 mm to 50 mm in 5 oscillations, and to 25 mm after 10 oscillations. (i) Show that the damping is exponential and calculate the ratio of successive amplitudes. (ii) Predict the amplitude after 20 oscillations.
Score 0 / 39 · 0 of 8 marked

This paper is written by Plasmo in the style of the OCR A-Level Physics exam. It is not a past paper and is not produced or endorsed by the exam board.

Fundamental data analysis Exam Questions: OCR A-Level Physics | Plasmo