IB Physics HL Topic 7 & 12 Study Guide Exam Questions And Actual Answers.
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Module
IB Physics
Institution
IB Physics
Outline the evidence that supports a nuclear model of the atom. - Answer GEIGER-MARSDEN EXPERIMENT:
•positive alpha particles fired at thin gold leaf
•expected to travel straight through
•some of alpha particles were deflected through huge angles
•numbers being deflected at any given...
IB Physics HL Topic 7 & 12 Study Guide
Exam Questions And Actual Answers.
Outline the evidence that supports a nuclear model of the atom. - Answer GEIGER-MARSDEN
EXPERIMENT:
•positive alpha particles fired at thin gold leaf
•expected to travel straight through
•some of alpha particles were deflected through huge angles
•numbers being deflected at any given angle agreed with an inverse square law of repulsion from the
nucleus
•evidence for electron energy levels comes from emission and absorption spectra
• existence of isotopes provides evidence for neutrons
Outline one limitation of the simple model of the nuclear atom. - Answer • doesn't explain why
electrons do not fall into nucleus
•model doesn't take into account isotopes which have varying atomic masses
Describe the emission spectra and absorption spectra. - Answer •when element given enough energy
emits light
•light can be analysed by splitting it into its various colours
•if all possible frequencies of light present, called continuous spectrum
• emission spectrum not continuous but contains only few characteristic colours (certain frequencies)
•same particular frequencies absent if continuous spectrum of light is shone through element in gaseous
form, called absorption spectrum
Outline evidence for the existence of atomic energy levels. - Answer •electrons can only occupy given
energy levels-energy of electron quantized
•energy levels fixed for particular elements and correspond to allowed orbitals
•when electron moves between energy levels it must emit or absorb energy
•energy emitted or absorbed corresponds to difference between two allowed energy levels
, •emission and absorption spectrum unique for each element
Describe photons. - Answer •energy emitted or absorbed in "packets' of light called photons
•higher energy photon corresponds to higher frequency (shorter wavelength) of light
ENERGY OF A PHOTON:
E=hf
Describe the interactions in a nucleus. - Answer •nucleons are arranged so that strong nuclear force of
attraction overcomes the coulomb force of repulsion between protons in the nucleus.
•nucleons need to be 1.3 femtometers apart for strong nuclear force to causes them to be attracted to
each other and be stable
•if distance more strong nuclear force does nothing
•if less it is strongly repulsive instead.
What are A, Z and N? - Answer Nucleon number (A)
Proton number (Z)
Neutron number (N)
Describe coulomb interaction. - Answer like charges i.e. protons repel one another by coulomb
interaction
Describe the phenomenon of natural radioactive decay. - Answer •Radioactive decay is a random and
spontaneous process which involves unstable nuclei emitting radioactive particles.
Describe the rate of decay. - Answer •The rate of decay decreases exponentially with time
•proportional to the number of atoms in the sample
•INDEPENDENT OF:
→temperature
→pressure
→chemical composition
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