Essential practical techniques in physics (1.2.2)
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Metre ruler
A metre ruler or half-metre ruler is the standard analogue apparatus for measuring lengths from a few millimetres up to Graduations are typically every giving a resolution of on a single reading and on a difference of two readings. The eye must be positioned directly above the scale to avoid parallax error.
Vernier callipers
Vernier callipers measure small lengths (typically up to ) to a resolution of (analogue) or (digital). They have external jaws for outer dimensions, internal jaws for inner dimensions, and a depth probe for hole or step depths.
Always check for zero error with the jaws closed. Record any offset and subtract it from each reading. The reading is taken as:
main scale + vernier scale × resolution
Tighten the jaws gently against the object: over-tightening compresses soft samples and gives a systematic underestimate.
Protractor
A protractor is the standard analogue apparatus for measuring angles. Standard semicircular protractors read with a resolution of
Align the centre cross-hair on the vertex and one light ray on the line, then read the angle off the scale. When measuring angles of refraction or diffraction, increase precision by drawing the ray as long as possible and taking the angle from a line through several points, not just two.
Newton meter
A Newton meter (spring balance) is an analogue device for measuring force directly in newtons. It uses an internal spring obeying Hooke’s law; extension is proportional to applied force. In school settings, Newton meters are typically available in ranges such as
Choose a range where the expected force sits near the middle of the scale to minimise fractional uncertainty. Always check for zero error with no load on the hook. Read at eye level to avoid parallax. Newton meters measure weight directly. To obtain mass, divide by the local value of
Ticker timer
A ticker timer is a mains-driven oscillating hammer that marks dots on a paper tape at (in the UK; matched to mains electricity), i.e. one dot every By attaching the tape to a moving object, distance–time information is captured, and velocity and acceleration can be deduced from gap spacing along the tape.
Count gaps, not dots, when working out time: For acceleration, measure two velocities at different points along the tape and use:
Friction between the tape and timer is a systematic error. This is a measurement method that requires minimal technology. Light gates or a data logger are preferable for high-precision work.
Liquid-in-glass thermometer
A liquid-in-glass thermometer is an analogue apparatus for measuring temperature. A reservoir of coloured spirit (or, in older instruments, mercury) at the bulb expands and rises up a narrow capillary against a calibrated scale. Typical school thermometers cover to with graduations.
Immerse the bulb fully and wait until the level stops rising before reading. Take the reading at eye level, at the top of the liquid column, to avoid parallax error. For Boyle’s law or specific heat capacity experiments, allow time for thermal equilibrium between the thermometer and the sample.
Analogue ammeter
An analogue ammeter measures electric current in a circuit using a moving-coil galvanometer with a calibrated scale. It is always connected in series with the component carrying the current. Typical school models offer ranges such as and on dual scales.
Choose a range where the expected current sits in the upper half of the scale to reduce fractional uncertainty. Read at eye level to avoid parallax.
Analogue voltmeter
An analogue voltmeter measures the potential difference (p.d.) across a component. It is connected in parallel with the component. School models commonly offer and ranges via a dual scale.
Choose a range where the expected p.d. sits near the upper end of the scale to minimise fractional uncertainty. A voltmeter has very high resistance, so adding it to a circuit branch should not significantly change the current.
Top pan balance
Top pan balances are less accurate than analytical balances but can be used for heavier samples. Their accuracy generally ranges from 1 to 3 decimal places.
The lack of draft exclusion makes weighing on a top pan balance more rapid.
Digital thermometer
Digital thermometers use a thermistor or thermocouple probe and display temperature on a liquid crystal display (LCD), typically to a precision of Thermocouples (a junction of two dissimilar metals generating a small electromotive force) can be used at much higher temperatures than liquid-in-glass thermometers, often above
Digital probes have low thermal mass and respond quickly, making them ideal for cooling curves and transient temperature changes. The probe must be fully immersed in the medium and not touching the container wall. As with all digital instruments, the displayed resolution sets the uncertainty of a single reading.
Digital multimeter
A digital multimeter (DMM) is a single digital instrument that can be set to measure current, voltage, resistance and (on most models) capacitance. It is the workhorse of A-level electrical practicals: it is used in resistivity, electromotive force/internal resistance and potential-divider experiments.
Always connect the voltmeter setting in parallel and the ammeter setting in series.
Hall probe
A Hall probe is a small digital instrument for measuring magnetic flux density, directly. A thin semiconductor wafer at the tip carries a known current; in a magnetic field, charge carriers are deflected sideways, producing a transverse Hall voltage that is proportional to and displayed in or on the meter.
The flat face of the sensor must be held perpendicular to the field for the maximum reading: tilting the probe gives a reduction. Zero the meter in a field-free region before each set of readings. Unlike a search coil, the Hall probe works in steady (DC) fields, so it is the natural choice for mapping the field of a bar magnet or determining inside a current-carrying solenoid.
Calorimeter
A calorimeter is a thermally insulated vessel, typically a copper cup wrapped in lagging, or an expanded-polystyrene cup. It is used to contain a substance whose specific heat capacity, or specific latent heat, is being determined. The lagging minimises heat loss to the surroundings during the measurement.
Set square
A set square is a rigid triangular ruler used to increase the accuracy of a length measurement by enforcing a perpendicular alignment. The two triangle types most frequently encountered are those with angles measuring and those with angles of
A set square is used to read a ruler at eye level, perpendicular to the scale, removing parallax error. It also ensures a ruler is held vertically (e.g. when timing a free-falling object, or measuring the amplitude of an oscillation), and that the normal drawn for refraction experiments is genuinely at to the boundary.
Plumb line
A plumb line is a small dense mass (the plumb bob) suspended from a thin string. Gravity defines the string as truly vertical once the bob is at rest. It is used to increase the accuracy of length and angle measurements by providing a reliable vertical reference.
It is useful when the workbench is not level. For example, when setting up a free-fall apparatus so the release point is directly above the landing point, or when checking that a retort stand and ruler are vertical for a pendulum experiment. The bob must be allowed to come to rest before any reading is taken.
Fiducial marker
A fiducial marker is a fixed reference point (e.g. a pin, line on a card, or notch on a stand) placed at the equilibrium position of an oscillating object. It defines a precise moment at which to start and stop the stopwatch when timing a period.
Stop-clock
A digital or analogue timer is used to measure time in seconds and minutes.
A digital stop clock or stop watch is often started at the beginning of the experiment in time dependent reactions and rate studies.
Light gates
Light gates are digital timing devices that start or stop an electronic timer or data logger when an infrared beam is interrupted. They eliminate human reaction-time error and are essential when time intervals are too short to be measured reliably with a stopwatch: e.g. free falling object, trolley collisions.
For instantaneous speed, time how long a card of known length takes to break the beam:
For acceleration, use two gates and either two cards or a card with two segments. Ensure the card passes perpendicular to the beam and that ambient light does not trigger the gate; align carefully before timing.
Digital multimeter
A digital multimeter (DMM) is a single digital instrument that can be set to measure current, voltage, resistance and (on most models) capacitance. It is the workhorse of A-level electrical practicals: it is used in resistivity, electromotive force/internal resistance and potential-divider experiments.
Always connect the voltmeter setting in parallel and the ammeter setting in series.
Analogue ammeter
An analogue ammeter measures electric current in a circuit using a moving-coil galvanometer with a calibrated scale. It is always connected in series with the component carrying the current. Typical school models offer ranges such as and on dual scales.
Choose a range where the expected current sits in the upper half of the scale to reduce fractional uncertainty. Read at eye level to avoid parallax.
Analogue voltmeter
An analogue voltmeter measures the potential difference (p.d.) across a component. It is connected in parallel with the component. School models commonly offer and ranges via a dual scale.
Choose a range where the expected p.d. sits near the upper end of the scale to minimise fractional uncertainty. A voltmeter has very high resistance, so adding it to a circuit branch should not significantly change the current.
DC power supply
A low-voltage DC power supply delivers a steady, adjustable direct current at outputs typically in the range Most have a built-in voltmeter or ammeter, a variable knob and may include current-limiting protection. They are used in place of cells and batteries for sustained or higher-current work.
Set to the lowest output before switching on. Connect red wires to red terminals and black wires to black terminals. Polarity matters for components such as diodes, electrolytic capacitors and motors. Allow time for the internal resistance of the supply to fall to a steady value before recording readings, and check the output with a multimeter rather than trusting the front-panel display alone.
Cells and batteries
Individual cells (e.g. dry cells) and assembled batteries are the standard EMF source for circuits where a stable output and a defined internal resistance are required.
Variable resistor (rheostat)
A variable resistor is a coil of wire wound on a former, with a sliding contact. It can be connected as:
- a rheostat with two terminals, A and B, which controls current.
- a potentiometer with three terminals, A, B and C, which can control p.d. by acting as a potential divider.
Use the rheostat configuration to vary current smoothly through a component when investigating characteristics. Use the potentiometer configuration to access a full range of p.d. from up to the supply voltage. This is essential when characterising a filament lamp or diode near zero.
Signal generator
A signal generator produces an alternating output (AC) of selectable waveform (sine, square, triangular), frequency (typically ) and amplitude. It is the standard AC source for driving loudspeakers, vibration generators and microwave transmitters in wave experiments.
Oscilloscope
An oscilloscope displays a voltage–time trace on a screen with a square grid (usually 1 cm divisions). The time-base sets the seconds per horizontal division; the Y-gain (volts/division) sets the vertical scale. It is used to measure amplitude, period (and hence frequency) and phase difference.
Read amplitude as Y-gain multiplied by the number of vertical divisions from the centreline to the peak. Read period as time-base times by the number of horizontal divisions for one complete cycle, then For the best precision, expand the trace so one cycle covers most of the screen.
Search coil
A search coil is a small flat coil of many turns of fine wire, connected to an oscilloscope or sensitive AC voltmeter. When placed in a changing magnetic field, an EMF is induced across its terminals (Faraday’s law). The peak induced EMF is proportional to the peak flux linkage through the coil.
Microphone and loudspeaker
A loudspeaker (driven by a signal generator) is the standard source of sound waves at chosen frequencies. A microphone converts incident sound back into an electrical signal that can be displayed on an oscilloscope or analysed by a data logger. Together they allow quantitative sound-wave experiments.
Ripple tank
A ripple tank is a shallow, transparent tank of water with a vibrating dipper (or straight bar) driven by a small motor. Ripples on the surface are projected onto a screen below by an overhead lamp, allowing wave behaviour to be observed:
- reflection
- refraction
- diffraction
- two-source interference.
Vibration generator
A vibration generator (or vibration transducer) is essentially a small loudspeaker without a cone, with a drive rod fixed to its diaphragm. Driven from a signal generator, it produces controlled mechanical oscillations used to set up stationary waves on a string or in a stretched wire.
Adjust the frequency of the signal generator until a clear stationary wave appears. Avoid resonance amplitudes large enough to detach the string.
Microwave transmitter and receiver
A microwave kit consists of a Gunn diode transmitter (typically with a wavelength of ) and a receiving probe connected to an amplifier or meter. The relatively long wavelength makes it ideal for demonstrating interference, diffraction, standing waves and polarisation on a macroscopic scale.
Resonance tube
A resonance tube is a vertical glass tube closed at one end (often by adjusting the water level inside) with a sound source held above the open end. When the source frequency matches a natural frequency of the air column, a stationary wave forms and the sound is audibly louder than the source. This is resonance.
Laser
A laser is a coherent, monochromatic, highly collimated light source. School lasers are generally red diode lasers ( or green diode-pumped lasers They are the source of choice for Young’s double-slit, single-slit diffraction and diffraction grating experiments.
Diffraction grating
A diffraction grating is a glass or plastic slide with a large number of equally spaced parallel lines (typically 300 to 600 lines per mm). When monochromatic light passes through, it produces sharp, bright maxima at angles given by the diffraction grating equation.
Polariser
A polariser is an optical filter that transmits only the component of incident light vibrating along its transmission axis, blocking the perpendicular component. Two polarisers in sequence demonstrate that light is a transverse wave; when their axes are crossed (at ), no light is transmitted
Geiger–Müller (GM) tube and counter
A Geiger–Müller (GM) tube is a detector of ionising radiation (α, β and γ). Each ionising event produces a pulse, which is registered by a counter (total counts in a chosen time) or a ratemeter (counts per second).
SAFETY: Handle sealed sources with tongs, keep them in their lead-lined storage when not in use, and minimise exposure time and handling distance. Always measure and subtract background count rate. The GM tube has a dead time so the maximum reliable count rate is limited; check sources of systematic error before taking measurements.