Pearson Edexcel International GCSE in Physics · 4PH1 · Free · no account needed
Physics required practicals
All 14 required practicals, in 17 procedures, for Pearson Edexcel International GCSE Physics (4PH1) on one page — the method step by step, the independent, dependent and control variables with the reason each one is held constant, and the sources of error classified as systematic, random or judgement. Each is taught inside its lesson, linked below.
The specification lists them as practical investigations; Pearson's UK GCSE calls the equivalent set core practicals, and students call them required practicals — this is that list for the International GCSE. They are examined in writing: "state a control variable and explain why it must be kept constant", "suggest an improvement", "explain why the result is anomalous". Every mark in those questions is a reason, not a step, which is why each practical here carries the reason beside each variable and the fix beside each error. Learn the method here; then open the lesson, understand the science the practical is testing, prove it in five marked questions, teach it back to an AI pupil and defend it in a short debate — the four things a method sheet cannot ask of you. Completely free.
The 14 practicals, 17 procedures
- investigating the motion of everyday objects — 1.5
- Practical — how the acceleration of a trolley depends on the force on it — Topic 1
- how extension varies with applied force — 1.22
- Practical — how the resistance of a wire depends on its length — Topic 2
- Investigating how current varies with voltage (statement 2.9) — Topic 2
- charging insulating materials by friction — 2.23
- Practical — measuring wave speed in a ripple tank and on a string — Topic 3
- refraction through rectangular, semi-circular and triangular blocks — 3.17
- measuring the refractive index of glass — 3.19
- investigating the speed of sound in air — 3.25
- investigating the frequency of a sound wave — 3.27
- investigating thermal energy transfer — 4.9
- measuring density from mass and volume — 5.4
- a temperature–time graph through a change of state — 5.11
- measuring specific heat capacity — 5.14
- plotting the field of one magnet and of two — 6.6
- investigating penetrating power — 7.6
Topic 1 · Forces and motion
1. Required practical (1.5): investigating the motion of everyday objects
Specification statement 1.5 · Topic 1 · taught in Speed, and What a Distance–Time Graph Is Telling You
Method
- Set light gates a measured distance apart, or mark the track at equal intervals.
- Fix a card of known length to the trolley so the gate times a known distance.
- The speed at that gate = length of the card ÷ the time the beam was interrupted.
- Release the trolley from the same marked point each run — release, never push.
- Record the time at each gate with a data logger.
- Repeat three times, take a mean, and identify any anomaly.
- Plot distance against time; draw a line of best fit; take the gradient over a large section.
Variables. Independent: distance along the track. Dependent: time taken. Control: release point, ramp angle, surface, mass of trolley — each changes the accelerating force or friction, so changing one would make the comparison invalid.
Sources of error and improvement. Systematic: reaction time (~0.2 s) applies at start and stop and is the same direction each run, so averaging cannot remove it — use light gates. Random: variation in release, and parallax when reading the rule — repeat, and read at eye level. Improve precision by timing over a longer distance, so the same uncertainty is a smaller percentage.
Understand the science behind it → · Prove it · Teach it · Defend it
2. Practical — how the acceleration of a trolley depends on the force on it
Topic 1 · taught in Resultant Force, Friction and F = ma
Method
- Place a trolley on a runway with a string over a pulley at the end, attached to a hanging mass holder.
- Fix a card of known length to the trolley and set up two light gates along the runway, connected to a data logger.
- Release the trolley from rest; the logger records the speed at each gate and the time between them.
- Calculate acceleration = change in speed ÷ time taken between the gates.
- Increase the force by moving a slotted mass from the trolley to the hanger, so the total mass accelerated stays the same.
- Repeat for at least five forces, three times each, and plot acceleration against force: a straight line through the origin shows a ∝ F.
- To investigate mass instead, keep the hanging mass fixed and add masses to the trolley.
Variables
Independent (changed) — The accelerating force (weight of the hanging masses)
Dependent (measured) — The acceleration of the trolley
| Control variable | Why it must be held constant |
|---|---|
| Total mass accelerated | a = F ÷ m, so changing mass would also change the acceleration |
| The same runway and trolley | a different surface changes friction |
| Angle of the runway | a slope adds part of the trolley's weight to the accelerating force |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | Friction opposes the motion, so every acceleration is lower than F ÷ m predicts. | Tilt the runway slightly until the trolley rolls at constant speed. |
| Random | Repeat runs give slightly different accelerations. | Repeat each force three times and calculate a mean. |
Understand the science behind it → · Prove it · Teach it · Defend it
3. Required practical 1.22 — how extension varies with applied force
Specification statement 1.22 · Topic 1 · taught in Hooke's Law and Elasticity
Method
- Clamp the spring vertically from a stand, with the stand weighted or clamped to the bench so it cannot topple.
- Measure the original length of the spring with a millimetre rule, with the rule vertical and the eye level with the marker.
- Hang a mass hanger from the spring and record the force in newtons, taking the weight of each 100 g slotted mass as approximately 1 N.
- Measure the new length and calculate the extension by subtracting the original length from it.
- Add masses one at a time, recording the force and the new length each time, for at least six values.
- Remove the masses one at a time and re-measure, to check whether the spring returns to its original length.
- Plot force on the vertical axis against extension on the horizontal axis, and draw a line of best fit through the straight region.
Variables
Independent (changed) — The force applied to the spring, in newtons
Dependent (measured) — The extension of the spring, in metres
| Control variable | Why it must be held constant |
|---|---|
| The same spring | different springs have different spring constants |
| Temperature | warming a spring changes its stiffness |
| Position of the rule | moving it between readings adds a false change in length |
| Time before reading | the spring must stop oscillating or the length is not steady |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | The original length is measured with the mass hanger already attached, so every extension is too small. | Measure the unloaded length before attaching anything. |
| Judgement | Reading the rule from above or below the marker gives a parallax error in the length. | Read the rule with the eye level with the marker. |
| Random | The spring is still oscillating when the length is read, so readings scatter. | Wait until the spring is completely still. |
Understand the science behind it → · Prove it · Teach it · Defend it
Topic 2 · Electricity
4. Practical — how the resistance of a wire depends on its length
Topic 2 · taught in Resistance and Ohm's Law
Method
- Tape a length of thin resistance wire (for example constantan) along a metre rule.
- Connect the wire in series with an ammeter and a low-voltage supply, using a crocodile clip fixed at 0 cm and a second clip that can slide along the wire.
- Connect a voltmeter in parallel across the length of wire between the two clips.
- Set the sliding clip at 10 cm, switch on briefly, record the current and the potential difference, then switch off.
- Repeat at 10 cm intervals up to 100 cm, then repeat the whole set and calculate a mean resistance R = V ÷ I for each length.
- Plot resistance against length: a straight line through the origin shows resistance is directly proportional to length.
- The same circuit can test combinations: two resistors in series give a larger total resistance; two in parallel give less than either one alone.
Variables
Independent (changed) — The length of wire between the clips
Dependent (measured) — The resistance, calculated from V ÷ I
| Control variable | Why it must be held constant |
|---|---|
| Material of the wire | different metals have different resistances for the same length |
| Thickness of the wire | a thinner wire has a higher resistance |
| Temperature of the wire | a hotter wire has a higher resistance, so keep the current small |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | The clips' contact point is not exactly at the marked length, so every length is off by the same amount. | Plot a graph; the gradient is unaffected by a constant offset. |
| Random | Meter readings fluctuate slightly as the clip contact changes. | Repeat each length and calculate a mean. |
| Systematic | Leaving the current on lets the wire heat up and its resistance rise. | Switch off between readings. |
Understand the science behind it → · Prove it · Teach it · Defend it
5. Investigating how current varies with voltage (statement 2.9)
Specification statement 2.9 · Topic 2 · taught in Current–Voltage Graphs, LDRs and Thermistors
Method
- Connect the component in series with a battery, an ammeter and a variable resistor, and connect a voltmeter in parallel across the component.
- Adjust the variable resistor to give the smallest voltage reading and record the voltage and the current.
- Increase the voltage in equal steps, recording the voltage and the current at each step, for at least six values.
- Switch off between readings so the component does not heat up more than necessary.
- Reverse the connections to the supply and repeat, so that the graph can be plotted in both directions.
- Plot current on the vertical axis against voltage on the horizontal axis and draw a smooth curve or line of best fit.
Variables
Independent (changed) — The voltage across the component, in volts
Dependent (measured) — The current through the component, in amperes
| Control variable | Why it must be held constant |
|---|---|
| The same component | a different component has a different characteristic |
| Temperature | resistance changes with temperature in most components |
| The same meters | different meters have different systematic errors |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | The meters do not read zero when disconnected, so every reading is shifted by the same amount. | Check and zero both meters before starting. |
| Systematic | Current is left flowing between readings, so the component heats up and its resistance rises. | Switch off between readings. |
| Random | The reading fluctuates while the variable resistor is being adjusted. | Wait for the reading to settle before recording it. |
Understand the science behind it → · Prove it · Teach it · Defend it
6. Required practical 2.23 — charging insulating materials by friction
Specification statement 2.23 · Topic 2 · taught in Static Electricity
Method
- Suspend a polythene rod horizontally in a paper stirrup hung from a thread, so that it can turn freely.
- Rub a second polythene rod with a dry woollen cloth and bring it near one end of the suspended rod, without touching it.
- Observe the direction in which the suspended rod turns, and record whether it was attracted or repelled.
- Repeat with a perspex rod rubbed with the same cloth, brought near the same charged polythene rod.
- Repeat each observation at least twice to check that the result is consistent.
- Conclude from the pattern: two rods of the same material rubbed the same way repel, and rods of different materials attract.
Variables
Independent (changed) — The material of the rod brought near the suspended rod
Dependent (measured) — Whether the suspended rod is attracted or repelled
| Control variable | Why it must be held constant |
|---|---|
| The suspended rod | a different rod may carry a different charge |
| The rubbing cloth | a different material transfers electrons the other way |
| Number of rubbing strokes | more rubbing transfers more electrons |
| Humidity of the air | damp air lets the charge leak away |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | Damp air or damp hands let charge leak away, so every result is weaker than it should be. | Work on a dry day with dry, clean apparatus. |
| Judgement | A small movement of the suspended rod is hard to read as attraction or repulsion. | Watch the first movement only, before it swings back. |
| Random | Draughts move the suspended rod independently of any electrostatic force. | Shield the apparatus from air currents. |
Understand the science behind it → · Prove it · Teach it · Defend it
Topic 3 · Waves
7. Practical — measuring wave speed in a ripple tank and on a string
Topic 3 · taught in The Wave Equation
Method
- Ripple tank: set a vibrating bar to make plane waves and shine a lamp above so the wave pattern shows on paper beneath.
- Measure the length spanned by ten wavelengths on the paper with a metre rule, and divide by ten to find λ.
- Count the waves passing a point in 10 s, and divide by 10 to find f; or read f from the signal generator.
- Calculate the wave speed from v = f × λ.
- String: stretch a string between a vibration generator and a pulley with a hanging mass, and adjust the frequency until a steady pattern of loops appears.
- Measure across as many loops as possible; each loop is half a wavelength, so λ = 2 × the length of one loop.
- Read the frequency from the signal generator and calculate v = f × λ.
Variables
Independent (changed) — The frequency set on the signal generator
Dependent (measured) — The wavelength measured
| Control variable | Why it must be held constant |
|---|---|
| Depth of water in the tank | the speed of water waves depends on the depth |
| Tension in the string (hanging mass) | the speed of a wave on a string depends on its tension |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Random | A single wavelength is small and the pattern moves, so one reading is imprecise. | Measure across ten waves and divide by ten. |
| Systematic | The shadow on the paper is larger than the real waves because the lamp's light spreads out. | Put a ruler in the water and scale readings by its shadow. |
Understand the science behind it → · Prove it · Teach it · Defend it
8. Required practical 3.17 — refraction through rectangular, semi-circular and triangular blocks
Specification statement 3.17 · Topic 3 · taught in Refraction and Refractive Index
Method
- Place the block on a sheet of paper and draw round its outline in pencil.
- Use a ray box with a single slit to send a narrow ray into one face of the block.
- Mark the path of the incoming ray with two pencil crosses well apart, and the emerging ray with two more.
- Remove the block and join the crosses with a ruler to reconstruct the ray paths, including the path inside the block.
- Draw the normal at each point where a ray meets a surface, and measure the angles with a protractor.
- Repeat with the semi-circular and triangular blocks, and describe how the emerging ray differs in each case.
Variables
Independent (changed) — The shape of the block, and the angle of incidence
Dependent (measured) — The angle of refraction, and the direction of the emerging ray
| Control variable | Why it must be held constant |
|---|---|
| The same glass block material | a different material has a different refractive index |
| Width of the ray | a broad ray cannot be marked accurately |
| Position of the block outline | moving the block after drawing loses the geometry |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Judgement | The ray has a visible width, so the exact centre of the line is a matter of opinion. | Mark the centre of the ray consistently each time. |
| Systematic | The block is nudged after its outline is drawn, so every measured angle is shifted. | Draw round the block and do not move it. |
| Random | Reading the protractor to the nearest degree scatters repeated measurements. | Repeat each angle and take a mean. |
Understand the science behind it → · Prove it · Teach it · Defend it
9. Required practical 3.19 — measuring the refractive index of glass
Specification statement 3.19 · Topic 3 · taught in Refraction and Refractive Index
Method
- Draw round a rectangular glass block on paper and mark the point where the ray will enter one long face.
- Draw the normal at that point, at right angles to the face.
- Direct a single ray at the marked point at an angle of incidence of about 20°, and mark the incoming and emerging rays with pencil crosses.
- Remove the block, join the crosses, and draw the path of the ray inside the glass between entry and exit.
- Measure the angle of incidence and the angle of refraction from the normal with a protractor.
- Repeat for angles of incidence of about 30°, 40°, 50°, 60° and 70°.
- Calculate n = sin i ÷ sin r for each pair and take a mean, or plot sin i against sin r and take the gradient.
Variables
Independent (changed) — The angle of incidence, in degrees
Dependent (measured) — The angle of refraction, in degrees
| Control variable | Why it must be held constant |
|---|---|
| The same glass block | the refractive index is a property of the material |
| The same face of the block | a chipped or uneven face changes the geometry |
| Temperature | refractive index varies slightly with temperature |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | The normal is drawn slightly off the perpendicular, so every angle pair is biased the same way. | Construct the normal with a set square. |
| Judgement | At very small angles of incidence the refracted angle is hard to distinguish from the incident one. | Use angles of incidence above about 20°. |
| Random | Marking the emerging ray with crosses too close together makes its direction uncertain. | Place the two crosses as far apart as possible. |
Understand the science behind it → · Prove it · Teach it · Defend it
10. Required practical 3.25 — investigating the speed of sound in air
Specification statement 3.25 · Topic 3 · taught in Sound Waves
Method
- Measure the distance from a clapping position to a large flat wall with a tape measure, using at least 50 m.
- Clap once and listen for the echo, then begin clapping in time with the returning echoes so that each clap coincides with the echo of the one before.
- Once the clapping is steady, start a stopwatch on one clap and count 20 further claps, stopping the watch on the twentieth.
- Divide the total time by 20 to find the time for one clap-to-echo interval.
- The distance travelled in that time is twice the distance to the wall, so calculate speed = 2 × distance ÷ time.
- Repeat the whole procedure three times and take a mean.
Variables
Independent (changed) — The distance from the wall, in metres
Dependent (measured) — The time for the sound to travel to the wall and back, in seconds
| Control variable | Why it must be held constant |
|---|---|
| The same wall | a soft surface gives a weak echo that is hard to hear |
| Air temperature | sound travels faster in warmer air |
| Background noise | other sounds make the echo hard to identify |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Judgement | Deciding exactly when the echo returns is difficult, and different people hear it slightly differently. | Clap in time with the echoes rather than judging one. |
| Random | Human reaction time of about 0.2 s scatters the stopwatch readings badly over a half-second interval. | Time 20 intervals at once and divide by 20. |
| Systematic | Measuring to the wrong point on the wall makes every distance, and so every speed, wrong by the same proportion. | Measure to the reflecting face of the wall. |
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11. Required practical 3.27 — investigating the frequency of a sound wave
Specification statement 3.27 · Topic 3 · taught in Oscilloscopes, Pitch and Loudness
Method
- Connect a microphone to the input of an oscilloscope and switch the time base on.
- Use a signal generator and loudspeaker to produce a steady note of known frequency, placed a fixed distance from the microphone.
- Adjust the time base until between two and four complete waves are visible across the screen.
- Count the horizontal divisions occupied by one complete wave, estimating the fraction of a division at each end.
- Multiply by the time base setting to find the period, convert it to seconds, and calculate the frequency from f = 1 ÷ T.
- Repeat for at least six different frequencies on the signal generator and compare the calculated values with the generator settings.
Variables
Independent (changed) — The frequency produced by the signal generator, in hertz
Dependent (measured) — The period measured from the trace, in seconds
| Control variable | Why it must be held constant |
|---|---|
| The time base setting | changing it mid-reading invalidates the conversion |
| Distance from loudspeaker | moving it changes the amplitude and can clip the trace |
| The same microphone | microphones respond differently across the range |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Judgement | Deciding exactly where one complete wave begins and ends on the screen. | Measure across several waves and divide. |
| Systematic | The time base is misread or set to a different value than assumed, biasing every frequency. | Check the time base setting before each reading. |
| Random | Background noise makes the trace unsteady, so the width read varies between attempts. | Work in a quiet room and repeat the reading. |
Understand the science behind it → · Prove it · Teach it · Defend it
Topic 4 · Energy resources and energy transfers
12. Required practical 4.9 — investigating thermal energy transfer
Specification statement 4.9 · Topic 4 · taught in Conduction, Convection and Radiation
Method
- CONDUCTION: take rods of copper, aluminium, steel and glass of the same length and diameter, and fix a drawing pin to the far end of each with a blob of wax.
- Place the near ends together in a trough of hot water and record the order in which the pins fall as the wax melts, which ranks the materials by how well they conduct.
- CONVECTION: drop a crystal of potassium manganate(VII) into one corner of a beaker of cold water and heat that corner gently, observing the coloured current rise, cross the surface and sink at the far side.
- RADIATION: fill two identical metal cans with the same volume of water at the same starting temperature, one painted matt black and one shiny.
- Place both the same distance from a radiant heater, or leave both to cool, and record the temperature of each every minute for fifteen minutes.
- Plot temperature against time for both cans on the same axes and compare the rates.
Variables
Independent (changed) — The surface or material being compared — the metal of the rod, or the colour of the can
Dependent (measured) — The time taken for the wax to melt, or the temperature of the water
| Control variable | Why it must be held constant |
|---|---|
| Volume of water | more water takes longer to change temperature |
| Starting temperature | the rate of transfer depends on the temperature difference |
| Distance from the heater | radiation received falls off sharply with distance |
| Dimensions of the rods | a thicker or shorter rod conducts faster |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | One can holds slightly more water than the other, so it changes temperature more slowly throughout. | Measure both volumes with the same measuring cylinder. |
| Judgement | Deciding the moment a blob of wax has melted enough for the pin to fall. | Record the time the pin actually drops. |
| Random | Draughts across the bench cool one can more than the other between readings. | Shield both cans from air currents. |
Understand the science behind it → · Prove it · Teach it · Defend it
Topic 5 · Solids, liquids and gases
13. Required practical 5.4 — measuring density from mass and volume
Specification statement 5.4 · Topic 5 · taught in Density
Method
- REGULAR SOLID: measure the length, width and height with a ruler or vernier callipers and calculate the volume.
- Find the mass on a balance, zeroed before use, and calculate density = mass ÷ volume.
- IRREGULAR SOLID: find its mass on the balance first, while it is dry.
- Part-fill a measuring cylinder with water, record the level, lower the object in on a thread until fully submerged, and record the new level.
- The volume of the object is the difference between the two readings; calculate the density as before.
- LIQUID: weigh an empty measuring cylinder, add the liquid, weigh again and subtract to find the mass of the liquid, reading its volume from the scale at eye level.
Variables
Independent (changed) — The material or object whose density is being found
Dependent (measured) — The density calculated, in kg/m³
| Control variable | Why it must be held constant |
|---|---|
| Temperature | density changes slightly as a material expands |
| The same balance | different balances have different zero errors |
| Object fully submerged | a partly submerged object displaces too little water |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | The balance is not zeroed, so every mass is out by the same amount. | Zero the balance before each set of readings. |
| Judgement | Reading the meniscus of the water from above rather than at eye level gives a parallax error. | Read the bottom of the meniscus at eye level. |
| Random | Air bubbles clinging to an irregular object make the displaced volume too large. | Tap the object to release trapped bubbles. |
Understand the science behind it → · Prove it · Teach it · Defend it
14. Required practical 5.11 — a temperature–time graph through a change of state
Specification statement 5.11 · Topic 5 · taught in Particles and Changes of State
Method
- Place crushed ice in a boiling tube with a thermometer, and stand the tube in a beaker of water heated gently and steadily by a Bunsen burner or an electric heater.
- Record the temperature every 30 seconds from before the ice begins to melt until well after all of it has melted.
- Stir gently and continuously so that the temperature is the same throughout the tube.
- Continue heating and recording until the water in the tube is boiling steadily.
- Plot temperature on the vertical axis against time on the horizontal axis.
- Identify the flat sections of the graph, which occur at the melting point and the boiling point, and note that the temperature is constant during each change of state.
Variables
Independent (changed) — Time, in seconds
Dependent (measured) — Temperature, in degrees Celsius
| Control variable | Why it must be held constant |
|---|---|
| Rate of heating | a changing rate distorts the shape of the graph |
| Mass of the substance | more substance takes longer to change state |
| Position of the thermometer | it must be in the substance, not touching the glass |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | The thermometer bulb touches the side of the tube and reads the glass rather than the contents. | Suspend the bulb in the middle of the substance. |
| Judgement | Reading a thermometer between two scale divisions requires an estimate that varies between readers. | Read to the nearest half division consistently. |
| Random | Without stirring, the temperature differs across the tube and readings scatter. | Stir gently and continuously throughout. |
Understand the science behind it → · Prove it · Teach it · Defend it
15. Required practical 5.14 — measuring specific heat capacity
Specification statement 5.14 · Topic 5 · taught in Specific Heat Capacity
Method
- For a solid, take a metal block of known mass with holes drilled for an electric immersion heater and a thermometer.
- Insulate the block, put a little oil in the thermometer hole for good thermal contact, and record the starting temperature.
- Connect the heater through a joulemeter, or through an ammeter and voltmeter with a timer so that the energy can be calculated from E = I × V × t.
- Switch on and record the temperature every minute for about ten minutes, then switch off and record the highest temperature reached.
- Calculate the temperature rise, and use c = Q ÷ (m × ΔT).
- For water, use a known mass of water in an insulated container with the same heater arrangement, stirring throughout.
Variables
Independent (changed) — The substance being heated
Dependent (measured) — The temperature rise produced for a measured energy input
| Control variable | Why it must be held constant |
|---|---|
| Energy supplied | the comparison is meaningless if the input differs |
| Mass of substance | a larger mass gives a smaller temperature rise |
| Insulation | uninsulated samples lose energy at different rates |
| Starting temperature | energy is lost faster when further above room temperature |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | Some energy warms the surroundings and the heater rather than the block, so the calculated value comes out too high. | Insulate the block and start below room temperature. |
| Systematic | Poor thermal contact between the thermometer and the block means it reads lower than the block's true temperature. | Put a little oil in the thermometer hole. |
| Systematic | Temperature keeps rising after the heater is switched off, so stopping early under-reads the rise every time. | Keep recording until the temperature stops rising. |
| Random | Thermometer and timer readings vary slightly from one run to the next. | Repeat the experiment and calculate a mean value of c. |
Understand the science behind it → · Prove it · Teach it · Defend it
Topic 6 · Magnetism and electromagnetism
16. Required practical 6.6 — plotting the field of one magnet and of two
Specification statement 6.6 · Topic 6 · taught in Induced Magnetism and Field Patterns
Method
- Place a bar magnet on a bench and lay a sheet of white card or paper over it, marking the outline of the magnet on the card.
- Sprinkle iron filings thinly and evenly over the card from a shaker, then tap the card gently until the filings settle into the pattern.
- Record the pattern by sketching it, and note where the filings are most densely packed.
- For the directions, clear the filings and place a plotting compass near one pole; mark a dot at each end of the needle.
- Move the compass so that its tail sits on the dot the head just made, mark the new head position, and repeat across the card.
- Join the dots into a smooth line and put an arrow on it in the direction the compass north pointed.
- Repeat the whole procedure with two magnets, first with UNLIKE poles facing across a gap, then with LIKE poles facing, marking any neutral point where the compass will not settle.
Variables
Independent (changed) — The arrangement of the magnets — one magnet, unlike poles facing, or like poles facing
Dependent (measured) — The shape and direction of the field pattern recorded on the card
| Control variable | Why it must be held constant |
|---|---|
| The gap between the two magnets | the pattern and the neutral point move if the separation changes |
| The same pair of magnets throughout | a stronger magnet shifts the neutral point towards the weaker one |
| No other magnets or iron nearby | any stray field adds to the one being plotted and distorts the pattern |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | Iron or steel in the bench or a nearby clamp adds its own field to every reading. | Plot the field on a wooden bench well away from ironwork. |
| Random | Filings sprinkled too thickly clump together and hide the individual lines. | Sprinkle thinly from a shaker and tap the card gently. |
| Judgement | Marking the compass dots imprecisely makes the plotted line drift away from the true field line. | Place each new dot exactly on the previous one. |
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Topic 7 · Radioactivity and particles
17. Required practical 7.6 — investigating penetrating power
Specification statement 7.6 · Topic 7 · taught in Alpha, Beta and Gamma
Method
- Measure the count rate with no source present, over a long count, to find the background rate.
- Place the sealed source in a holder a fixed short distance from a Geiger–Müller tube, handling it only with long tongs.
- Record the count over a measured time with nothing between source and detector, and subtract the background to get the corrected count rate.
- Place a sheet of paper between the source and the detector and repeat the measurement.
- Replace the paper with a few millimetres of aluminium and repeat.
- Replace the aluminium with a thick sheet of lead and repeat.
- Identify the radiation: stopped by paper means alpha; passing paper but stopped by aluminium means beta; still detected through lead means gamma.
- Return the source to its lead-lined store as soon as the readings are finished.
Variables
Independent (changed) — The absorbing material placed between the source and the detector
Dependent (measured) — The corrected count rate registered by the Geiger–Müller tube
| Control variable | Why it must be held constant |
|---|---|
| The distance from source to detector | the count rate falls sharply with distance, which would be mistaken for absorption |
| The counting time for each reading | a longer count gives a larger total, so the readings would not be comparable |
| The same source throughout | different sources have different activities and emit different radiations |
Sources of error
| Type | What goes wrong | What to do |
|---|---|---|
| Systematic | Background radiation adds to every reading and is always present. | Measure the background and subtract it from every count. |
| Random | Decay is random, so repeated counts over the same time differ from one another. | Count for a long time and repeat, then take a mean. |
| Judgement | Absorbers of different thickness are compared as though they were equivalent. | Use the standard thicknesses of paper, aluminium and lead. |
Understand the science behind it → · Prove it · Teach it · Defend it
From the method to the mark
A method is a list until you can say why each line is there. Each lesson linked above explains the science first, then asks you to prove it, teach it and defend it.
- Every Physics lesson — Physics on Incandio, topic by topic.
- Physics key terms — every definition to learn word for word.
- Physics equations — every formula with its symbols and units.
- The 4PH1 specification · Incandio Science