Tuesday, 23 September 2014

Atomic Struture Questions


Question 1
a)Give a brief description of Rutherford’s alpha particle scattering experiment.
b)State the main conclusions of the experiment.
c)An SYGMA particle of mass 6·68×10-27kg, is moving straight towards a gold nucleus (Z = 79) at a speed of 0·01c (0·01 times the speed of light). Calculate the minimum distance between the two particles (the distance of closest approach).
Question 2
a)Bohr developed a model of the hydrogen atom.
i)What particles enter into this model?
ii)Describe the motion he assumed for each of the particles.
iii)What forms of energy did he include when calculating the total energy of the atom?
 iv)What does it mean to describe a physical quantity as being "quantized"?
v)Which quantity did Bohr consider to be quantized when developing his model?
b)Use Bohr’s theory to explain why hydrogen emits a line spectrum rather than a continuous spectrum.
Question 3
In a simplified version of Millikan’s oil drop experiment, a drop of radius r = 1·710-3mm, is between two parallel metal plates separated by distance d = 9mm.
When the voltage across the plates is V = 2kV, the drop remains stationary. The density of the oil isPSMALL = 800kgm-3. Use this information to estimate the number of singly ionised atoms in the drop.
Question 4
The diagram below represents the energy levels in a hydrogen atom.
a)Convert the energies into Joules.
b)Calculate the wavelength of the radiation given out by each of the three transitions shown on the diagram. In each case state whether the quantum of radiation is in the u.v., the visible or the i.r. part of the spectrum.
c)Calculate the wavelength of the radiation needed to ionise a hydrogen atom which is in its ground state. Answer in Joules.
d)Calculate the energy of an electron in level n = 5. Answer in electron-volts.
Question 5
a)Discuss briefly deBroglie’s hypothesis and mention one experiment which gives evidence to support it.
b)
Calculate the wavelength of the “deBroglie wave” associated with an electron in the lowest energy Bohr orbit. (The radius of the lowest energy orbit according to the Bohr theory is 5·10-11m.)
Question 6
a)
Draw a labelled diagram of an X-ray tube.
b)Explain the characteristic (or line) part of an X-ray spectrum.
c)Derive a formula to calculate the minimum wavelength of X-rays in the continuous part of an X-ray spectrum.
Use your formula to calculate the highest frequency of X-rays given by a tube which uses a high voltage supply of 25kV.
Question 7
Calculate the wavelengths of the “deBroglie” waves associated with
a)1kg mass moving at 50ms-1
b)an electron which has been accelerated by a p.d. of 500V.
Question 8
How much energy could (in principle) be obtained from 1u of mass? (Answer first in J then in MeV.)
Question 9
A proton has a mass of 1·0078u and a neutron has a mass of 1·0078u. A helium nucleus has a mass of 4·0026u. Calculate the energy given out when a helium nucleus is formed. Answer in MeV.
Question 10
The fission of a uranium 235 nucleus into barium and krypton produces about 200MeV of energy. Find the mass loss during this reaction. (Answer first in kg then in u.)
Question 11
The neutron was discovered when beryllium was bombarded with SYGMA particles. Copy and complete the following equation which describes the reaction.
Question 12
A uranium 235 nucleus can decay into a thorium (Th) nucleus by the emission of an  particle. Write an equation which describes this decay.
Question 13
Copy and complete the following equation which describes a possible nuclear fission process.
Question 14
A neptunium nucleus (Np 239) can decay into a plutonium nucleus (Pu 239) and a  particle. Write an equation to describe this reaction.