Topic 6.1: Experimental Skills Questions

A ray of light passes from air into a glass block.

A student uses a protractor with a resolution of 1° to measure the angle between the refracted ray and the normal.

State this measured angle and its absolute uncertainty if the refracted ray crosses the protractor scale at the 33° mark.

In an experiment to find the resistivity of a metal rod, a student measures the rod's diameter with a micrometer at several different positions along its length and takes the mean.

Outline why the diameter is measured at several positions rather than just once.

A liquid's density is found to be ρ = 1.03 ± 0.04 g cm⁻³.

State the density and its absolute uncertainty in kg m⁻³, with appropriate precision.

A nail is driven into wood.

The total length of the nail is measured with a ruler as 32.4 ± 0.1 cm and the length sticking out above the wood is 8.7 ± 0.1 cm.

The embedded depth is the difference of these two readings.

State the embedded depth and its absolute uncertainty.

In a double-slit experiment the fringe separation s is measured for several screen distances D.

Theory predicts s = (λ/a)·D, where λ is the wavelength and a is the slit separation.

The student plots s on the vertical axis and wants a straight line through the origin so the gradient gives λ.

State the quantity that should be plotted on the horizontal axis.

An experiment requires the length of a straight resistance wire, which is about 85 cm long.

Suggest a suitable instrument for measuring this length and justify your choice.

To find the spring constant of a spring, a student plots the applied force F (in newtons) on the y-axis against the extension x (in metres) on the x-axis and obtains a straight line through the origin.

State the SI units of the gradient of this graph.

A wire obeys Ohm's law, so the potential difference V across it is directly proportional to the current I through it (V = R·I).

A student plots V on the vertical axis against I on the horizontal axis.

Sketch the expected graph, and state what its gradient represents.

A class is collecting data on how the pressure of a fixed gas sample depends on its volume, by pushing in a sealed syringe and reading a pressure gauge.

State one variable that must be controlled during the experiment.

A marker sinks to a depth d under a water pressure P, and theory predicts d = k√P.

To linearize the data the student plots depth d (vertical) against root-pressure √P (horizontal).

One table row reads P = 16.0 kPa and d = 5.2 cm.

Determine the coordinates of the point this row should be plotted at on the graph.

Two power supplies are connected in series.

Their voltages are V₁ = 6.0 ± 0.3 V and V₂ = 9.0 ± 0.2 V.

State the total voltage of the combination and its absolute uncertainty.

Before plotting a sin(i) against sin(r) graph for a refraction experiment, a student needs to finish processing the data.

One row records the angle of refraction as r = 42.0°.

Calculate the value of sin r to be entered in that row, giving your answer to three significant figures.

A student investigates how the current I through a component varies with the voltage V across it.

Theory predicts I = k·V² (the current is proportional to the square of the voltage).

State what the student should plot on each axis to obtain a straight line through the origin, and state what the gradient of that line represents.

A nail is partly hammered into a block of wood.

A student rests a metre rule against the wood to measure the length of nail sticking out.

Describe two considerations when positioning and reading the rule so that the length is measured accurately.

A student measures how the deflection of a light ball on a long thread changes when a horizontal electric force is applied.

They are told to make the thread much longer than the gap between the charged plates.

Explain why a much longer thread gives a more reliable measurement of the electric force.

Two students process the same five repeated readings of a quantity.

Student X quotes the mean as 3.7, while Student Y quotes it as 3.74186.

Discuss which way of quoting the mean is more appropriate for these readings, which were each measured to two significant figures.

In a diffraction experiment a student measures the separation of bright fringes on a screen.

A single fringe spacing is about 3 mm and is hard to read precisely with a ruler.

Describe a method that reduces the absolute uncertainty in the fringe separation, and explain why it works.

A student times the swings of a pendulum with a stopwatch whose smallest division is 0.01 s, but their reaction time is much larger than this.

Describe how the student can obtain the period with an uncertainty far smaller than their reaction time would allow.

A student records five micrometer readings of a wire's diameter in millimetres: 0.38, 0.39, 0.38, 0.51, 0.39.

Show that the mean diameter, after discarding any anomalous reading, is about 0.39 mm.

A student needs to measure the thickness of a single sheet of aluminium foil, expected to be about 0.02 mm.

Suggest a suitable instrument and justify your choice by reference to its resolution.