OCR A Level Physics A: Practical Endorsement skills, apparatus and techniques (H556) – Revision Notes

These notes condense OCR A Level Physics A (H556), section 1.2.1 (practical skills) and section 1.2.2 (apparatus and techniques), from the OCR specification, Version 3.0 (March 2026). For full explanations and worked examples, read the study guide. Test yourself with the practice set. Hub: OCR A Level Physics. Printable checklist. Find weak spots with the free 10-minute diagnostics. For planning, analysis and evaluation see Development of practical skills.

The endorsement in brief

• Teacher assessed, reported separately; it does not contribute to the overall A level grade.
• A minimum of 12 practical activities covering PAG1 to PAG12, plus consistent, routine display of the CPAC.
• You may work in groups but must show your own competence and keep your own record.

PAG	Topic	PAG	Topic
1	Motion	7	Ionising radiation
2	Properties of materials	8	Gases
3	Electrical properties	9	Capacitors
4	Electrical circuits	10	Simple harmonic motion
5	Waves	11	Investigation
6	Quantum effects	12	Research skills

The five CPAC competencies

1. Follows written procedures.
2. Applies investigative approaches and methods when using instruments and equipment.
3. Safely uses a range of practical equipment and materials.
4. Makes and records observations.
5. Researches, references and reports.

1.2.1 Skills at a glance

Ref	Skill	Remember
(a)	Investigative approaches	Variables: independent, dependent, controlled; solve practical problems
(b)	Safe, correct use	Hazard, harm, control; minimise risk
(c)	Follow instructions	In order; note any change
(d)	Observations and measurements	Record as you go
(e)	Records	Dated, complete, include repeats
(f)	Presentation	Tables, graphs, units, consistent decimal places
(g)	Software and tools	Spreadsheet, graph software, check by hand
(h)	Research	Websites, textbooks, printed sources
(i)	Citing	Author or organisation, year, title, web address, date accessed
(j)	Wide range of instruments	Every item under 1.2.2

Method for a risk assessment

1. Name the hazard (for example a laser beam).
2. Say what could be harmed and how (retina damage from direct or reflected light).
3. State a specific control (low power, never look along the beam, remove reflective objects, stop the beam with a screen).
4. Say what to do if something goes wrong (switch off, report it).

1.2.2 Apparatus at a glance

Ref	Apparatus	Key technique
(a)	Analogue: ruler, thermometer, protractor, newton meter, pressure gauge, measuring cylinder	Eye level, avoid parallax, interpolate between marks
(b)	Digital: multimeter, balance, timer	Ammeter in series, voltmeter in parallel, ohmmeter with no power; check range and zero
(c)	Accuracy methods	Time many oscillations; fiducial marker at equilibrium; set square for right angles; plumb line for vertical
(d)	Stopwatch or light gates	Light gates remove reaction time; card width measured accurately
(e)	Vernier and micrometer	Check zero error, ratchet on micrometer, average several readings
(f)	Build from a diagram	Series loop first, add voltmeters last, check polarity
(g)	Design and check circuits	Calculate component values, then measure to check
(h)	Signal generator and oscilloscope	Y-gain in V/div, time-base in s/div
(i)	Waves	Microphone and loudspeaker; ripple tank; vibration transducer; microwave or radio source
(j)	Laser or light source	Interference and diffraction
(k)	ICT	Modelling, data logger with sensors, software processing
(l)	Ionising radiation	Detector, background count, safe handling

Formulas and relationships

Situation	Relationship
Oscillation period	T = total time / number of oscillations
Percentage uncertainty	(absolute uncertainty / value) × 100
Micrometer	main scale reading + thimble reading − zero error
Oscilloscope p.d.	divisions × volts/division
Oscilloscope period	divisions per cycle × time/division, then f = 1/T
Light gate speed	card width / time to pass
Series resistor	R = (supply p.d. − component p.d.) / current
Double slit	λ = a w / D
Diffraction grating	d sin θ = nλ, with d = 1/(lines per metre)
Corrected count rate	source count rate − background count rate
Count uncertainty	about √N for N counts

Reading a micrometer, step by step

1. Close the jaws gently with the ratchet and note the zero error (reading above zero is positive).
2. Place the object between the jaws and tighten with the ratchet only.
3. Read the sleeve, including the half-millimetre mark if it is visible.
4. Add the thimble reading in hundredths of a millimetre.
5. Subtract the zero error. Repeat at other positions and average.

Reading an oscilloscope, step by step

1. Note the Y-gain (V/div) and time-base (time/div) settings.
2. Count the vertical divisions peak to peak and multiply by V/div, then halve for the peak value.
3. Count the horizontal divisions for one cycle and multiply by time/div to get T.
4. Find f = 1/T.

Worked reminders

Multiple oscillations. 10 oscillations take 14.6 s. T = 14.6 / 10 = 1.46 s. A ±0.2 s timing error gives ±0.02 s in T, about 1.4 %.

Grating. 600 lines per mm gives d = 1.667 × 10⁻⁶ m. For light of wavelength 650 nm in the first order, sin θ = 650 × 10⁻⁹ / 1.667 × 10⁻⁶ = 0.39, so θ = 23.0°. Measuring the angle on both sides of the central maximum and averaging helps check that the grating is square to the beam.

Radiation. Background 72 counts in 300 s is 0.24 s⁻¹. A source giving 1944 counts in 60 s is 32.4 s⁻¹. Corrected rate: 32.4 − 0.24 = 32.2 s⁻¹.

Must-know distinctions

• Resolution is the smallest change an instrument shows; accuracy is how close a reading is to the true value; precision describes the spread of repeats.
• A zero error shifts every reading by the same amount; random scatter changes from one reading to the next.
• A fiducial marker marks a position for starting and stopping timing; a plumb line marks the vertical.
• Background count is present with no source and must be subtracted; absorber measurements also need it removed.
• Series places a meter in the current path; parallel places it across the component.

Safety with sources, lasers and circuits

• Radioactive sources: keep in the storage container when not in use, handle with tongs, point away from people, short time and large distance, follow your centre’s rules.
• Lasers: lowest suitable power, never look into the beam or a reflection, keep the beam below eye level, stop it with a screen.
• Circuits: use a low current, switch off before changing connections, check wires are not hot.

Quick self-test

1. A 60 mm length is measured with a ruler to ±0.5 mm. What is the percentage uncertainty?
2. A trace has 4.0 divisions per cycle on 2 ms/div. What is the frequency?
3. A trace is 6.0 divisions peak to peak at 0.2 V/div. What is the peak p.d.?
4. A micrometer shows sleeve 7.5 mm and thimble 12 divisions. The zero error is +0.04 mm. What is the corrected reading?
5. Why is timing 20 oscillations better than timing one?
6. A 0.080 m card passes a light gate in 0.020 s. What is its speed?
7. An LED needs 1.8 V at 10 mA from a 5.0 V supply. What series resistor value is needed?
8. A grating has 300 lines per mm and the first order is at 11.5°. What is λ?
9. Background: 100 counts in 200 s. Source: 5400 counts in 60 s. What is the corrected rate?
10. Name two controls for a laser hazard.

Answers

1. 0.5 / 60 × 100 = 0.83 %.
2. T = 4.0 × 2 ms = 8 ms, f = 1 / 0.008 = 125 Hz.
3. Peak-to-peak = 6.0 × 0.2 = 1.2 V, peak = 0.60 V.
4. 7.5 + 0.12 = 7.62 mm; 7.62 − 0.04 = 7.58 mm.
5. The fixed timing error is shared over 20 periods, so the percentage uncertainty in T is 20 times smaller.
6. 0.080 / 0.020 = 4.0 m/s.
7. R = (5.0 − 1.8) / 0.010 = 320 Ω.
8. d = 3.33 µm; λ = 3.33 × 10⁻⁶ × sin 11.5° = 665 nm.
9. Background 0.50 s⁻¹; source 90.0 s⁻¹; corrected 89.5 s⁻¹.
10. Any two: low-power laser, never look into the beam, remove reflective objects, stop the beam with a screen, warning notice.

Where marks are usually lost

• Writing “wear goggles” for every hazard without linking the control to the apparatus.
• Reading a micrometer without the zero error or the half-millimetre mark.
• Misreading volts per division, or using the time-base setting for the voltage axis.
• Quoting the time for one oscillation when asked for the method that increases accuracy.
• Placing a voltmeter in series or an ammeter in parallel on a circuit sketch.
• Not subtracting background count, or not stating that it was measured separately.
• Recording data with mixed decimal places, or with units missing from table headings.
• Giving a source as “the internet”, or no citation at all.
• Saying a digital reading is “exact” instead of giving its resolution.

Official syllabus

OCR, A Level Specification Physics A (H556), Version 3.0 (March 2026), for first assessment in 2017: sections 1.2.1, 1.2.2 and 5g.