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Rutherford devised an experiment to fire alpha particles at thin gold foil - Edexcel - GCSE Physics: Combined Science - Question 5 - 2022 - Paper 1
Question 5
Rutherford devised an experiment to fire alpha particles at thin gold foil. It was found that alpha particles were scattered by the gold foil. The gold foil was 4.0 ... show full transcript
Worked Solution & Example Answer:Rutherford devised an experiment to fire alpha particles at thin gold foil - Edexcel - GCSE Physics: Combined Science - Question 5 - 2022 - Paper 1
Step 1
Estimate how many gold atoms would fit across this thickness of gold foil.
Answer
To find the number of gold atoms that would fit across 4.0 × 10⁻⁷ m, use the following calculation:
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First, convert the gold atom's diameter from nanometers to meters:
0.15 nm = 0.15 × 10⁻⁹ m = 1.5 × 10⁻¹⁰ m.
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Next, divide the thickness of the gold foil by the diameter of one gold atom:
Number of atoms = (Thickness of gold foil) / (Diameter of gold atom) = (4.0 × 10⁻⁷ m) / (1.5 × 10⁻¹⁰ m) = 2.67 × 10³.
Therefore, approximately 2,700 gold atoms would fit across the thickness of the gold foil.
Step 2
Estimate the ratio of the number of particles scattered through 5° to the number of particles scattered through 100°.
Answer
Referring to Figure 7:
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From the graph, read the number of particles scattered at 5°; let’s say this is approximately between 10⁶ and 10⁷.
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Read the number of particles scattered at 100°; let’s assume this value is approximately 10².
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Ratio of particles scattered:
= (Number of particles scattered at 5°) : (Number of particles scattered at 100°) = (between 10⁶ and 10⁷) : (10²).
Therefore, the ratio is roughly between 10⁴:1 and 10⁵:1.
Step 3
Explain how the difference in the number of particles scattered at different angles gives evidence for the current model of the structure of the atom.
Answer
The experiment shows that:
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Most alpha particles pass straight through the foil without scattering, indicating that atoms are mostly empty space.
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Some alpha particles are scattered at small angles, which suggests the presence of a positively charged nucleus within the atom that causes these deflections.
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Very few alpha particles are deflected at large angles, implying a concentrated mass (the nucleus) that is small and dense, supporting the notion of the nuclear model of the atom.
In conclusion, the observed scattering illustrates that atoms have a nucleus surrounded by a cloud of electrons, reinforcing the modern atomic model.
Step 4
Describe how the students could use the apparatus to model the scattering of alpha particles.
Answer
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The students can roll a marble down the movable slope towards the circular weight (representing the atomic nucleus).
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As the marble hits the circular weight, it can scatter off in various directions, modeling how alpha particles interact with gold atoms.
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Students should observe the trajectory of the marble as it rebounds to understand scattering, much like alpha particles being deflected by the nucleus of an atom.
Step 5
Give one limitation of this model.
Answer
One limitation of this model is that it does not account for the quantum nature of particles; real alpha particle scattering involves wave-particle duality and interactions at the atomic level, which cannot be accurately represented through a simple marble-and-slope model.