Slides in this set
Describe how a fluorescent tube works in terms of excitation and de excitation
of electrons (6)
·Fluorescent tube contains a gas, mercury.
·The gas is electrically disturbed (a high voltage passed through the tube)
·The electrically disturbed electrons in the mercury gas excite into higher energy
levels (but not ionised)
·These excited electrons quickly de-excite to return to the stable ground state,
releasing UV photons of energy hf = E1 - E2 (change in energy levels)
·The UV photons have a high energy due to high frequency and absorbed by the
fluorescent coating of the tube.
·The electrons within the fluorescent coating excite to high energy levels.
·Upon de-excitation emits many different photons of visible light, creating a full
spectrum which makes the tube fluoresce white.
UV photon released upon de
excitation of electrons in
mercury gas…read more
The photoelectric effect suggests that electromagnetic waves can exhibit
particle like behaviour. Explain what is meant by threshold frequency and
why the existence of a threshold frequency supports the particle nature of
·Threshold frequency is the minimum energy (hf) needed for a photon to
overcome the work function for emission of electrons
·hf = + Ek (threshold frequency is when Ek is considered to be 0)
·Below this threshold frequency no emission will occur, even if INTENSITY IS
·Wave theory cannot explain this as energy of waves should increase with
·So light travels as packages, known as photons
·Electromagnetic waves are then considered to be particle like. As one photon is
absorbed by one electron.…read more
Describe the procedure the student would follow in order to obtain accurate
and reliable measurements of the resistance of the thermistor at different
· Thermistor is connected in a suitable circuit with voltmeter and ammeter
Thermistor is heated in a water bath and a thermometer is used to measure the
temperature at small regular intervals.
· The water must be stirred to ensure that the thermistor is at the temperature
measured by the thermometer.
·Resistance is found at various temperatures by dividing voltage by current.
· Give some indication of the range of temperatures to be used.
·To secure reliable results, repeat whole experiment and take more then one
measurements at each temperature to get a reliable mean.
·Plot a graph of resistance on y axis against temperature on x axis.
·To improve accuracy use more precise data measurers and a digital
Jan 09: When light of a certain frequency is shone on a particular metal surface,
electrons are emitted with a range of kinetic energies. Explain in terms of photons why
electrons are released from the metal surface and why the kinetic energy of the emitted
electrons varies up to a maximum value
·June 09: Electrons with a range of kinetic energies strike atoms of a particular element
which are in their ground state. As a result of these collisions photons of various
frequencies are emitted by some of the atoms. Explain what is meant by the ground state
of an atom and describe the process that is taking place in the atoms emitting photons.
·Jan 10: experiment question on resistivity of a particular material
·June 10: experiment question on resistance of a thermistor at different temperatures-
·Jan 11: The photoelectric effect suggests that electromagnetic waves can exhibit
particle like behaviour. Explain what is meant by threshold frequency and why the
existence of a threshold frequency supports the particle nature of electromagnetic
·June 11: Line spectra were observed before they could be explained by theory. We now
know that photons of characteristic frequency are emitted when the vapour of an
element is bombarded by energetic electrons. The spectrum of the light emitted contains
lines, each of a definite wavelength.
Explain how the bombarding electrons cause the atoms of the vapour to emit photons
and the existence of a spectrum consisting of lines of a definite frequency supports the
view that atoms have discrete energy levels.
·Jan 12: experiment question on resistance of wire at different temperatures- WATER