OCR A-level Physics Notes (New Spec) Full & Revised with Complete Solutions for Final Exam.
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OCR A-level Physics Notes (OCRALEVELPHYSICS)
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The University Of Warwick (UoW)
OCR A-level Physics Notes (New Spec) Full & Revised with Complete Solutions for Final Exam. Particles and Radioactivity
Alpha Particle Scattering Experiment
Plum Pudding model of the atom
● Atoms made up of a large mass of positive matter with a few negatively charged
electrons spread with...
ocr a level physics notes new spec full amp revised with complete solutions for final exam
ocr a level physics notes new spec full amp revised with complete solutions
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OCR A-level Physics Notes (OCRALEVELPHYSICS)
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OCR A-level Physics Notes (New Spec) Full & Revised wi
Complete Solutions for Final Exam.
,Particles and Radioactivity
Alpha Particle Scattering Experiment
Plum Pudding model of the atom
● Atoms made up of a large mass of positive matter with a few negatively charged
electrons spread within it
Rutherford’s experiment disproved the Plum Pudding model
Rutherford's alpha scattering experiment:
● Stream of alpha particles from a radioactive source was fired at a thin gold foil (only a
few atoms thick)
● The alpha particles were scattered by the foil and detected on a screen, which produced
a speck of light
Conclusions:
● Most of the alpha particles went straight through the foil
○ So the atom is mostly empty space
● Some alpha particles were deflected through large angles, so the centre of the atom
must have a large positive charge to repel them (the nucleus)
● Some particles were reflected angles larger than 90 degrees, so the nucleus must be
very small and has a high mass
,The nucleus
Proton number = number of protons in the nucleus - atomic number, Z
Nucleon number = the number of protons and neutrons - the mass number, A
Isotopes have the same proton number but a different number of neutrons. They will also have
the same charge and the same chemical properties.
The number of neutrons affects the stability of the nucleus, unstable nuclei may be radioactive
Nuclear radius is proportional to the cube root of the nucleon number
● Diameter of an atom is 0.1nm and the diameter of a nucleus is around 1fm
The nucleus of an atom is very small, massive and is therefore very dense
● Nuclear density is higher than atomic density
, The strong nuclear force
The strong nuclear force is an attractive force that overcomes the electrostatic repulsive force
between the positive charges of protons
● Has a short range, can only hold nucleons together when they are separated y a few
femtometers
● The strength of the strong nuclear force falls quickly beyond this distance
● The strong nuclear force works equally between all nucleons
● At very small separations, the strong nuclear force must be repulsive otherwise it would
crush the nucleus to a single point
1) Strong nuclear force is repulsive for very small separations (below 0.5fm)
2) After 0.5fm, the force becomes attractive and reaches a maximum, and then falls to zero
3) After around 3fm, it can no longer hold the nucleons together
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