Extension + Working Scientifically Skills AT3 Prep Yr7 2025 MHS

Stepped leader

A channel of negative charge that moves downward from a cloud toward the ground during the start of a lightning strike.

Return stroke

The powerful upward discharge from ground to cloud that we see as the bright lightning flash after the stepped leader connects.

Ferromagnetic materials

Materials (e.g., iron, nickel, cobalt) that are strongly attracted to magnets and are good cores for electromagnets.

Compass behaviour

A compass needle aligns with the local magnetic field; the needle points toward the magnetic north of the field being measured.

Magnetic vs non-magnetic materials

Magnetic materials (ferromagnetic) are strongly attracted to magnets; non-magnetic materials (wood, plastic) show no attraction.

SI units to remember

Always include units: mass (kg), weight/force (N), distance (m, cm, mm, µm), time (s), energy (J).

SI prefixes

kilo (k = 10³), milli (m = 10⁻³), micro (µ = 10⁻⁶) — useful for microscope scales and unit conversions.

Total magnification formula

Total magnification = eyepiece magnification × objective magnification (e.g., 10× × 40× = 400×).

Estimate specimen size from FOV

Specimen size = fraction of FOV × FOV diameter. First find FOV at that magnification, then multiply by fraction.

Units & showing working

Always show full working with units in calculations (e.g., W = m×g → 2 kg × 9.8 m/s² = 19.6 N).

Random vs systematic error

Random errors vary between trials (reduced by repeats); systematic errors shift all results (fixed by calibration).

Percent error (simple)

Percent error = |measured − true| / true × 100% — useful for assessing accuracy in practicals.

Graph reading tip (LOBF)

Line of Best Fit should show general trend; don’t dot-to-dot. Use it to interpolate values and describe trend (increase/decrease/plateau).

Word-list exam tip

Memorise exact phrasing from the word list for Part B — tests often require exact keywords.

Exam logistics reminder

Part A = 30 MCQ (2B pencil), Part B = 10 word defs (one-word/short), Part C = 20 marks (show working, units, diagrams). 5 min reading + 70 min working time.

Analog measurement

Device that indicates a value via a mechanical movement or pointer on a scale.

Digital measurement

Device that displays a numeric value on a digital screen.

Range

The maximum and minimum values a measuring device can accurately measure.

Sensitivity

The smallest change in a quantity that a device can detect.

Accuracy

How close a measured value is to the true or accepted value.

Precision

How close repeated measurements are to one another (consistency).

Calibration

Adjusting a device using a known standard so its readings are accurate.

Repeat readings

Taking multiple measurements to assess precision and identify anomalies.

Average (mean)

Calculate the sum of repeated measurements and divide by the number of trials to reduce random error.

Outlier

A measurement that is very different from other repeated values and may be excluded if justified.

Qualitative data

Non-numerical observations describing qualities or characteristics.

Quantitative data

Numerical measurements that can be analysed statistically (e.g., mass, time, length).

Observation

To notice or record events using the senses or instruments.

Physical quantity

A measurable property (e.g., mass, length, time, temperature).

Instrument range

Choose a tool where expected values fall well within its max and min to avoid truncation.

Appropriate sensitivity

Select equipment that can detect the smallest meaningful change for your experiment.

Validity

The degree to which an investigation measures what it is intended to measure (fair test).

Reliability

The extent to which repeated trials produce similar results (repeatability).

Controlled variable

A factor kept constant to ensure a fair test.

Independent variable

The variable the experimenter deliberately changes (plotted on the x-axis).

Dependent variable

The variable measured/responding to changes in the independent variable (plotted on the y-axis).

Hypothesis

A testable prediction about the relationship between independent and dependent variables.

Procedure (planning)

Numbered steps you will follow written in present tense with exact quantities and units.

Method (reporting)

The written account of what you actually did, in past tense, incorporating any changes.

Risk assessment

Table of hazards, risks and specific minimisation steps for safety during the practical.

Hazard

A source of potential harm in an experiment (e.g., hot plate, chemicals, sharp glass).

Minimisation (control)

Specific actions to reduce the chance of harm (e.g., PPE, safe handling steps).

Scientific table rules

Include title, column headings with units, independent variable in first column, neat ruler-drawn borders.

Table units

Place units in the column heading only; numbers in the body have no units next to them.

Graph type selection

Line graph for trends/continuous data; column graph for discrete comparisons.

Graph axes rules

Independent variable on horizontal axis, dependent on vertical axis; include labels and units.

Graph scale

Start at zero when practical, choose even intervals, use at least half of each axis, mark scales clearly.

Plotting points

Mark data points clearly (e.g., X) and do not join dots; draw a smooth line/curve or a straight LOBF as appropriate.

Line of Best Fit

Single straight line or smooth curve representing the trend; aim for similar numbers of points above and below.

Interpolation vs extrapolation

Interpolation estimates within data range (ok); extrapolation predicts outside range (less reliable).

Recording trials

Record trial 1, trial 2, trial 3 and compute the average to improve precision.

Error sources

List possible systematic and random errors and state how you minimised them.