Experimental Design (OCR AS Physics): Exam Questions

A metal strip has thickness t, as shown below.

Five measurements of the thickness t at different positions along the length of the strip are shown below.

Determine the percentage uncertainty in the thickness t.

percentage uncertainty = ..................................................... %

A student wants to determine the Young modulus E of the metal of the strip in (a).

The student clamps the metal strip to the edge of a table using a G-clamp. A mass is permanently fixed to the end of the strip as shown.

The mass oscillates freely when it is moved away from its equilibrium position and then released.

The Young modulus E of the metal can be determined using the equation

$E=\frac{16{\pi }^{2}m{L}^3}{w{t}^3{T}^2}$

where m is the mass fixed to the end of the strip, L is the length of the strip from the end of the table to the centre of the mass, w is the width of the strip, t is the thickness of the strip, and T is the period of oscillations.

Describe how an experiment may be safely conducted, and how the data can be analysed to determine an accurate value for E.

This question is about a light-dependent resistor (LDR).

A student connects a potential divider circuit as shown below. It contains an LDR.

The fixed resistor has resistance 1500 Ω. The battery has electromotive force (e.m.f.) 12 V and negligible internal resistance. The voltmeter has extremely high resistance.

(i) When the LDR is covered, its resistance is 3000 Ω.

Calculate the voltmeter reading.

voltmeter reading = ..................................................... V

[2]

(ii) When fully illuminated, the resistance of the LDR is 100 Ω.

Show that the voltmeter reading changes by more than 7 V.

[1]

The current in an LDR depends on the intensity of light incident on it.

A student decides to alter the intensity of light incident on an LDR by using sheets of tracing paper and a light source.

The diagram below shows part of an arrangement suggested by the student.

It is suggested that the current I in the LDR is given by the expression

$I=k{e}^{-nx}$

where x is the total thickness of the sheets of tracing paper, and k and n are constants.

Describe how the student could carry out an experiment to verify the validity of this expression and determine k and n. Include in your answer

• a circuit diagram

• a possible table for the results, including the headings

• the graph plotted to determine k and n

• any precautions taken to improve the quality of the results.