Practical Investigation — practice questions

State the minimum number of values of the independent variable required for this standard, and state one reason why collecting more than the minimum is better.

A student writes the conclusion: "The graph was a curve, so the relationship is non-linear." Explain why this conclusion would not reach Merit, and rewrite it so that it would.

A student proposes to investigate how the current through a resistor depends on the voltage across it. Evaluate this choice as an investigation for AS91168, and suggest a change that would make it suitable.

A student investigates how the current $I$ through a lamp depends on the voltage $V$ across it. Identify the independent and dependent variable.

Explain why a trial run, before collecting the full set of results, improves the quality of an investigation.

A student's pendulum investigation used only three lengths, all between 40 cm and 45 cm, with a single reading at each length. Evaluate this design and explain what should change.

A student times a pendulum by measuring 10 complete oscillations and dividing by 10. State the name given to this kind of improvement, and state what it improves.

Explain why using a fiducial marker at the centre of a pendulum's swing gives more accurate timings than starting and stopping the stopwatch at the highest point of the swing.

A student investigating how the illuminance from a lamp depends on distance takes single readings with a light meter, in a room with the ceiling lights on and a window nearby. Evaluate the accuracy of this method and justify two specific changes.

State which variable goes on each axis of your graph, and state two things every axis label must include.

A student calculates the gradient of their linearised graph using two points taken straight from their results table. Explain why this reduces the quality of their analysis, and explain what they should do instead.

A student's linearised graph has five points lying close to a straight line through the origin and one point well above the line. Discuss how they should handle this point in their analysis and in their write-up.

A student suspects $y = kx^2$. State what should be plotted on each axis to produce a straight line, and what the gradient of that line represents.

A log–log plot of resistance $R$ against wire length $l$ gives a straight line with gradient $1.0$. Explain what this shows about the relationship between $R$ and $l$.

A student plots raw bounce height $h$ against drop height $H$ and gets a curve that looks almost straight near the origin. They conclude the relationship is linear without linearising. Evaluate this conclusion.

Three repeated length measurements are $20.1$ cm, $20.3$ cm, $19.9$ cm. Find the mean and the uncertainty using half the range.

Explain the difference between the reliability and the validity of an investigation, using an example of an investigation that could be reliable but not valid.

A student's best-fit line through error-bar data has gradient $2.1$. The steepest acceptable line (through the error bars) has gradient $2.4$, and the shallowest has gradient $1.8$. State the gradient with its uncertainty, and explain what this uncertainty means for the student's conclusion about the power $n$ in $y = kx^n$.

A student plots $v^2$ against $h$ and obtains a straight line through the origin.

State the type of relationship between $v$ and $h$.

A student plots $v^2$ (m² s⁻²) against $h$ (m) and obtains a straight line through the origin with gradient $19.4$.

Write the mathematical relationship obtained from this data, including the unit of the gradient, and state the relationship between $v$ and $h$.

A student's conclusion reads: "My graph was a straight line, which proves that the period is proportional to the square root of the length, as the theory says."

Evaluate this conclusion and rewrite it to a standard that would earn full credit.

State one variable that should be controlled in an investigation of how the period of a pendulum depends on its length, and state how you would keep it constant.

Explain why there is a practical limit to the smallest value of pendulum length that can usefully be investigated.

In an investigation of how illuminance $E$ from a lamp depends on distance $d$, a student obtained $E = 12/d^2$ but noticed that the points at the largest distances sat consistently above the line on their $E$ against $1/d^2$ graph.

Discuss this unexpected result: suggest a cause, explain how it would produce this specific pattern, and evaluate its effect on the validity of the conclusion.