Q5 · 2020 · Paper 2Complex familiar4 marks
QUESTION 5 (4 marks)
An electron is situated halfway between two nuclei that are separated from each other by a distance of 4.5× 10-10 m. The first nucleus contains two protons. The second nucleus contains three protons. Calculate the magnitude of the overall electromagnetic force experienced by the electron.
WORKED SOLUTION
4 marksQCAA guide · typeset solution
ANSWER
See worked solution below.
Worked solution
𝐹𝐹2 =
1
4𝜋𝜋𝜀𝜀𝑜𝑜
𝑄𝑄1 × 𝑞𝑞𝑒𝑒
𝑟𝑟1
2
= 9 × 109 × 3(1.6 × 10−19) × 1.6 × 10−19
(2.25 × 10−10)2
= 1.3 × 10−8N
𝐹𝐹1 =
1
4𝜋𝜋𝜀𝜀𝑜𝑜
𝑄𝑄2 × 𝑞𝑞𝑒𝑒
𝑟𝑟2
2
= 9 × 109 × 2(1.6 × 10−19) × 1.6 × 10−19
(2.25 × 10−10)2
= 9.0 × 10−9N
|𝐹𝐹𝑛𝑛𝑛𝑛𝑛𝑛| = |𝐹𝐹1| −|𝐹𝐹2|
= 1.4 × 10−8 −9.1 × 10−9
Force = 4.0 × 10−9 N (to 1 decimal place)
• indicates an understanding of the physical
scenario in relation to Coulomb’s law [1 mark]
• provides pertinent mathematical operation/s
correctly performed [1 mark]
• determines the forces (or electric field strength)
imposed by each nuclei on the electron [1 mark]
• determines the correct net force [1 mark]
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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