Leaving Cert Physics diagrams
Eight labelled Physics diagrams explained: the apparatus, measurements and ideas behind pendulums, momentum, refraction, lenses, diffraction, circuits and electric fields.
· Drawings by Ben
Know what each line is doing
A useful Physics diagram explains how something works. These eight drawings connect the labels to the measurements, equations and ideas you need when answering a question.
Try sketching each one from memory, then compare the labels and explain the measurement or result aloud. In an exam, include the apparatus and detail the particular question asks for; a diagram accompanies your written explanation.
The examples below come from earlier Higher Level papers. Their topics also appear in the Physics specification introduced in September 2025. This is a selection for revision; your course covers more than these eight examples.
Jump to a diagram:
- Measuring g with a simple pendulum
- Conservation of momentum on an air track
- Snell’s law and the refractive index of glass
- Measuring the focal length of a converging lens
- Measuring wavelength with a diffraction grating
- Ohm’s law: current and voltage in a metal wire
- A virtual image in a converging lens
- The electric field between parallel plates
Diagram 1 of 8
Measuring g with a simple pendulum
This arrangement lets you find the acceleration due to gravity, g, from the pendulum’s length and the time it takes to swing.
What to label
- A clamp stand, split cork, string and bob, with a timer beside them.
- The length l runs from the point of suspension to the centre of the bob. Use a metre rule to measure it.
Keep the swing small. Time several complete oscillations and divide the total time by their number to find the period, T. One complete oscillation returns to the same position while moving in the same direction.
Repeat for different lengths. Plot T2 vertically against l horizontally. The relationship T2 = (4π2/g)l gives g = 4π2/slope. Use lengths in metres and times in seconds to obtain g in m s−2.
Check your answer. Measuring to the bottom of the bob makes the length too large. Timing one crossing instead of a full oscillation makes the period too short. Mark the centre of the bob and define your starting point before timing.
Past-paper example: 2026 Higher Level, Question 2.
Diagram 2 of 8
Conservation of momentum on an air track
Two riders collide and stick together. Comparing their total momentum before and after the collision tests conservation of momentum.
What to label
- A level air track, riders A and B, and Velcro on their facing ends.
- Two photogates connected to a timer: one measures A before the collision and the other measures the joined riders afterwards.
Weigh both riders, including anything attached to them. Start B at rest between the gates. Send A through the first gate towards B, then let the joined riders pass through the second gate. The air track reduces friction so the external horizontal force is small.
For a photogate, speed is the length of the flag interrupting the beam divided by the interruption time. With B initially at rest, compare mAu with (mA + mB)v. They should agree within the uncertainty of the measurements.
Check your answer. The joined riders have both masses after the collision. Comparing A’s momentum alone before and after misses the momentum transferred to B. Also use the flag length, not the distance between the gates, for each interruption time.
Past-paper example: 2020 Higher Level, Question 1.
Diagram 3 of 8
Snell’s law and the refractive index of glass
A narrow ray changes direction as it enters a glass block. Measuring the two angles lets you test Snell’s law and calculate refractive index.
What to label
- A ray box, glass block, incident ray, refracted ray and emergent ray.
- A normal at right angles to the surface, with i and r measured between their rays and that normal; a protractor measures the angles.
Trace the block on paper and mark the path of the ray. Change the incident angle and collect several pairs of readings. For light entering glass from air, n = sin i / sin r.
A graph of sin i vertically against sin r horizontally should follow a straight line through the origin, allowing for measurement uncertainty. Its slope is the refractive index. Use the calculator’s degree mode when your measurements are in degrees.
Check your answer. Angles are measured from the normal, not the glass surface. Plot the sines of the angles rather than the angles themselves. Reversing the axes gives 1/n as the slope.
Past-paper example: 2025 Higher Level, Question 4.
Diagram 4 of 8
Measuring the focal length of a converging lens
A converging lens forms a sharp, real image of an illuminated object on a screen. The object and image distances give the focal length.
What to label
- An illuminated cross-thread in a ray box, a convex lens and a screen, aligned at the same height.
- u from the object to the lens, and v from the lens to the screen. Measure these distances with a metre rule.
Place the object farther from the lens than its focal length. Move the screen until the image is sharp, then measure u and v. The thin-lens equation is 1/f = 1/u + 1/v, so f = uv/(u + v).
Change the object position, refocus the screen and calculate another value of f. Average the focal lengths. Keep the same unit throughout: distances in centimetres give a focal length in centimetres.
Check your answer. Both distances start at the lens. The object-to-screen distance is u + v, not v. A blurred patch on the screen does not give a reliable image position: find the sharpest image before measuring.
Past-paper example: 2024 Higher Level, Question 2.
Diagram 5 of 8
Measuring wavelength with a diffraction grating
A laser passing through a diffraction grating produces bright spots on a screen. Their positions let you calculate the wavelength of the light.
What to label
- The laser, diffraction grating and screen, with the central spot labelled n = 0 and successive orders on either side.
- D from the grating to the screen and y from the central spot to the chosen spot. A metre rule measures the distances.
Find the angle of the chosen order from tan θ = y/D. Then use nλ = d sin θ, where d is the spacing between neighbouring grating lines. If the grating has N lines per metre, d = 1/N.
Measure matching orders on both sides of the centre and average the resulting wavelengths. If you measure the full separation of the two first-order spots, halve it to obtain y. Keep the beam below eye level and never look into it.
Check your answer. Lines per millimetre must be converted before finding d in metres. Keep the order n with its own angle: a second-order spot needs n = 2. The central spot fixes the zero direction; it cannot determine wavelength by itself.
Past-paper example: 2026 Higher Level, Question 3.
Diagram 6 of 8
Ohm’s law: current and voltage in a metal wire
Measure the current through a metal wire and the potential difference across it. At constant temperature, voltage and current should be proportional.
What to label
- A supply and a rheostat used as a potential divider to vary the voltage.
- An ammeter in the current path and a voltmeter connected across the metal wire.
Adjust the potential divider and record pairs of voltage and current readings. Use small currents and switch off between readings to limit heating: changing the wire’s temperature changes its resistance.
Plot voltage V vertically against current I horizontally. A straight line through the origin supports Ohm’s law at constant temperature. Its slope is the resistance, R = ΔV/ΔI, in ohms when current is in amperes.
Check your answer. The voltmeter belongs across the wire, not in series with it. If the graph instead has current vertically against voltage horizontally, the slope is 1/R. Convert milliamperes to amperes before calculating resistance.
Past-paper example: 2024 Higher Level, Question 5.
Diagram 7 of 8
A virtual image in a converging lens
A converging lens acts as a magnifying glass when the object lies between the lens and its focal point. The image is upright, enlarged and virtual.
What to label
- A principal axis, a converging lens, a focal point F on each side and an object inside the focal length.
- Two rays from the top of the object: one parallel to the axis and one through the optical centre. Add arrows showing the actual light travelling towards and through the lens.
The parallel ray refracts through the focal point on the far side. The ray through the optical centre continues straight in the thin-lens model. After the lens, the rays spread apart.
Extend the outgoing rays backwards using dashed lines. Their extensions meet on the object’s side of the lens, locating the top of the virtual image. The eye sees the rays as if they came from that point; the light does not actually travel along the dashed extensions.
Check your answer. A virtual image cannot be formed on a screen. Keep backward extensions dashed and actual light paths solid. Moving the object outside the focal length changes the kind of image, so check the object’s position first.
Past-paper example: 2026 Higher Level, Question 8.
Diagram 8 of 8
The electric field between parallel plates
Field lines show the direction of force on a positive test charge and the relative strength of the electric field between oppositely charged plates.
What to label
- Two parallel plates, one positive and the other negative.
- Straight, parallel, evenly spaced field lines in the central region, with arrows pointing from the positive plate towards the negative plate.
The even spacing represents an approximately uniform field away from the edges: a given charge experiences approximately the same force wherever it is in that central region. The lines bend near the edges, where this uniform-field approximation breaks down.
A positive charge is pushed along the arrows. A negative charge, such as an electron, experiences a force in the opposite direction. Field lines do not cross, because the field has one direction at any particular point.
Check your answer. Arrows show the force on a positive charge, not the direction an electron accelerates. Label both plates and include arrowheads; unlabelled parallel lines do not specify the field direction.
Past-paper example: 2016 Higher Level, Question 12(b).
Sources and what to practise next
The drawings are Ben’s own, also used alongside Physics marking schemes on PointsGame. The exam references identify earlier questions where the corresponding diagram is used. Written explanations and measurements still matter, and the official marking scheme sets the marks for each question.
- NCCA Leaving Certificate Physics specification: forces and momentum (§1.2), measuring g (§1.5), refraction and lenses (§2.3), diffraction (§2.6), electric fields (§3.2) and circuits (§3.3).
- Curriculum Online’s Physics page lists the current specification and the syllabus examined up to June 2026.
- State Examinations Commission exam archive provides the official past papers and marking schemes. PointsGame is independent of the SEC.
Practise the explanation as well as the picture with Physics past papers on PointsGame (sign-in required). Read how we organise questions by topic, or use spaced repetition to revisit the diagrams you find hardest.
Something wrong or unclear? Email help@pointsgame.ie.