Edexcel A-Level Physics Point-Charge Electric Fields

Practise Edexcel A-Level Physics point-charge electric fields by calculating field strength around nuclei, spheres and paired charges.

Exam points

calculate electric field strength from a point charge using the inverse-square formula
combine fields from two charges by deciding whether field directions add or subtract
interpret how electric field strength varies with distance from a positive point charge

[Maximum number: 3]

In the early 20th century, experiments were carried out in which alpha particles were directed towards thin gold foil.

A simplified diagram of the apparatus used is shown.

Figure for Question 4.4.95 - Electric field due to a point charge question 1 — Edexcel A-Level Physics A2

One experiment used gold foil made from the gold isotope ${ }_{79}^{197} \mathrm{Au}$ . The alpha particles had an initial kinetic energy of 4.7 MeV .

Calculate the strength of the electric field due to the gold nucleus at this distance.

Strength of electric field =

Use $E=kQ/r^2$ , with Q=79e: $E=\frac{(8.99\times10^9)(79)(1.60\times10^{-19})}{(4.8\times10^{-14})^2}=4.9\times10^{19}\,\mathrm{N\,C^{-1}}.$

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4.4.95 - Electric field due to a point charge question 1