During the 1870s Crookes investigated cathode rays using vacuum tubes like that shown below - Leaving Cert Chemistry - Question 5 - 2015
Question 5
During the 1870s Crookes investigated cathode rays using vacuum tubes like that shown below.
(a)
(i) Give one way of detecting the presence of cathode rays in a vac... show full transcript
Worked Solution & Example Answer:During the 1870s Crookes investigated cathode rays using vacuum tubes like that shown below - Leaving Cert Chemistry - Question 5 - 2015
Step 1
Give one way of detecting the presence of cathode rays in a vacuum tube:
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Answer
One way of detecting the presence of cathode rays in a vacuum tube is by observing the fluorescence or glow produced when the rays strike a phosphorescent material or the glass of the tube.
Step 2
Name the scientist who around 1897 identified cathode rays as subatomic particles and, using a vacuum tube, measured their charge-to-mass ratio:
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Answer
The scientist is J.J. Thomson.
Step 3
What name was given to the subatomic particle he identified?
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Answer
The name given to the subatomic particle is the electron.
Step 4
Name one of the three scientists who shared the 1903 Nobel prize in Physics for their pioneering work on radioactivity which provided evidence for subatomic particles.
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One of the scientists is Henri Becquerel.
Step 5
State three observations made by Rutherford’s team when they bombarded gold foil with alpha-particles:
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Answer
Most alpha-particles were undeflected and passed straight through the gold foil.
Some alpha-particles were slightly deflected from their original paths.
A few alpha-particles were reflected back.
Step 6
Explain how Rutherford deduced from these observations that the nucleus is positive:
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Answer
Rutherford concluded that the nucleus is positive because the deflection of some alpha-particles indicated a repulsive force acting upon them, suggesting the presence of positively charged particles within the nucleus.
Step 7
Explain how Rutherford deduced from these observations that the nucleus is small and dense:
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Answer
Rutherford inferred that the nucleus is small and dense because only a few alpha-particles were reflected back, indicating that the nucleus must occupy a very small volume within the atom, and their deflection required a substantial amount of mass concentrated in a small region.
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