BIG STRUGGLES Flashcards
(13 cards)
Fluorescent tube
Fluorescent tubes are partially evacuated glass tubes filled with low-pressure mercury vapour with a phosphor coating on the glass
How is light emitted from a fluorescent tube
When a high voltage is applied across the tube, electrons flow from the cathode to the anode producing an electron beam
These beam electrons collide with the electrons in the mercury atoms transferring kinetic energy in the collision
The atomic electrons in the mercury atoms are excited and move to a higher energy level
This high energy level state is unstable and so the electrons de-excite i.e. move back to their original ground state
As they de-excite, the electrons release that energy by emitting photons in the UV range of wavelengths
The UV photons then collide with electrons in the atoms of the phosphor coating and excite them into a higher energy level
As these phosphor electrons de-excite, they do so in stages emitting photons in the visible light range of wavelengths
What is the difference in calculating time constant for a charging and discharging capacitor.
Charging - 63% of the initial value
Discharging - 37% of the initial value
When and Who had the FIRST proposition when it came to the development of the nucleus and what did he propose?
1803 - Dalton - Billiard ball:
Atoms cannot be broken down,
Atoms of a given element are identical to each other,
When chemical reactions occur, the atoms rearrange to make different substances
When and Who had the SECOND proposition when it came to the development of the nucleus and what did he propose?
1897 - J.J Thomson - Plum pudding:
Thomson discovered the electron,
The atom consists of positive and negative charges in equal amounts so that it is neutral overall
Atoms can be modelled as spheres of positive charge with uniformly distributed charge and density.
When and Who had the THIRD proposition when it came to the development of the nucleus and what did he propose?
1909-1911 - Rutherford, Geiger, Marsden - Gold foil experiment:
Atoms are mostly empty space,
Atoms have a central, positively charged nucleus containing the majority of the mass.
When and Who had the FOURTH proposition when it came to the development of the nucleus and what did he propose?
1913 - Bohr - Planetary model:
Electrons orbit the nucleus, like planets around a star,
Electrons occupy well-defined shells or energy levels around the nucleus.
When and Who had the FIFTH proposition when it came to the development of the nucleus and what did he propose?
1926 - Erwin Schrödinger - Quantum mechanical model:
This model can be portrayed as a nucleus surrounded by an electron cloud
Where the cloud is most dense, the probability of finding the electron is greatest, and vice versa
What breakthrough in the change of the model of a nucleus happened in 1932 and why was it significant?
James Chadwick discovered the neutron, which added an unaccounted mass and completed the atom model.
What is the typical radius of a nucleus?
1x10^-15 m
Which gives a more accurate value for the diameter of a nucleus: Closest approach estimation or High-energy electron diffraction
And why?
High-energy electron diffraction
Electrons are not subject to the strong nuclear force so electron scattering patterns are easier to interpret
Electrons give greater resolution
or electrons are more accurate because they can get closer
or α particles cannot get so close to the nucleus because of electrostatic repulsion
What potential difference should the electrons be accelerated through to achieve the wavelength required for High-energy Electron diffraction
W = qV
W = Ke
Therefore:
V=Mv^2 / 2q
State Lenz Law
When a current is induced by electromagnetic induction, the direction of the induced emf and current is always such as to oppose the charge that causes it.
