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Edexcel A-Level Physics Uncertainty and Errors

Practise Edexcel A-Level Physics uncertainty and systematic error sources using resolution limits, zero errors, parallax and percentage uncertainty.

Syllabus
Pearson Edexcel International Advanced Subsidiary/Advanced Level
Course
Physics XPH11/YPH11
Level
AS

Exam points

  • explain how resolution, flash duration or parallax changes measurement uncertainty
  • identify systematic-error sources such as omitted mass, misaligned normals or zero error
  • reduce percentage uncertainty by measuring multiple identical objects together

3.3.9 - Uncertainty and systematic error sources question 1

[Maximum number: 4]

A student investigated the photoelectric effect using the apparatus shown.

Figure for Question 3.3.9 - Uncertainty and systematic error sources question 1 — Edexcel A-Level Physics AS

He used a source of white light and colour filters to shine different wavelengths λ\lambda of light onto the photocell.

Photoelectrons were emitted with a range of kinetic energies, creating a small current in the photocell.

Using the potentiometer, the student varied the potential difference across the photocell. As the potential difference across the photocell increased, the current in the photocell decreased.

He measured the potential difference VsV_{\mathrm{s}} when the current in the photocell was zero.
He calculated the maximum kinetic energy Emax E_{\text {max }} of the photoelectrons for each wavelength of light.

The student's investigation involves a small random error and a large systematic error.

For each of these, suggest a source of the error and a realistic modification to the procedure which would reduce it.

Random error:
Systematic error:

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