Download VCE UNIT 4 SAC

VCE UNIT 4 SAC
LIGHT & MATTER
MaterialsYou may bring into the SAC pens etc and a scientific calculator.
You are also allowed one half sheet of handwritten or typed notes that have been submitted to me, these
will be handed back to you with the other SAC material.
You will also be given the relevant formulae and values for constants (see below) as would be available
on the external examination.
You will be provided with graph paper.
TasksAs you have been earlier informed the SAC will be split into two sections- a Data Analysis and a Test
section. The Data Analysis section will account for approximately 2/3 of the total marks for this SAC.
The Data Analysis section is based on data obtained from two experiments that mi were performed in
the Australian Synchrotron laboratory i.e .Photoelectric Effect and Double-Slit Interference.
Time AllowedYou are allowed 5 minutes reading time and 95 minutes of writing time.
Formulae and values
Photoelectric effect
Photon energy
Photon momentum
De Broglie wavelength
Mass of the electron =
Charge on the electron =
Planck's constant =
Speed of light =
Ek max = hf - W
E = hf
p = h/
 = h/p
9.1 x 10-31 kg
-1.6 x 10-19 C
6.63 x 10-34 Js = 4.14 x 10-15 eVs
3 x 108 m/s
Data Analysis Question 1
Information- A circuit was set up to demonstrate the photoelectric effect. The circuit was set up with
reverse bias. Radiation was directed onto a plate (initially Metal A) and measurements were made of
the potential difference between the plates and the current flowing in the circuit. For a variety of
radiation wavelengths a current was measured in the circuit and this current was then reduced to zero by
adjusting the potential difference between the plates. For each situation the wavelength of the radiation
and the potential difference that caused the current to fall to zero were recorded.
Initial dataWavelength
(nm)
Potential
Difference (V)
472
505
525
588
611
6.4 x 10-1
4.9 x 10-1
4.0 x 10-1
1.4 x 10-1
6.9 x 10-2
(a) Calculate the frequency for each of the radiation wavelengths in the table. Show (for at least one
case) how this was calculated.
(b) On the graph paper provided draw a graph of EK max versus frequency (ensure you make the graph
sufficiently large to show relevant features clearly, do not mark in anything else until asked)
(c) From your graph clearly show how to obtain values for fo, h and W and find these values.
(d) Draw a circuit diagram to represent the situation used to obtain these values.
(e) The original metal plate (Metal A) that the radiation is directed on is now replaced by a different
plate (Metal B), the new plate has a work function that is 0.2 eV greater in magnitude than the
original plate. Draw a graph to represent this second plate on your original graph and label them
clearly Metal A and Metal B.
(f) Now consider a particular frequency that is greater than fo (in both cases) that is used on both Metal
A and then Metal B (one after the other). Sketch a current versus voltage graph for both of these on
the same set of axes no actual values are required. Clearly indicate which graph is for Metal A
and which is for Metal B.
(g) Sketch another graph of current versus voltage for Metal A and then indicate clearly (can do it on
the graph or just describe) what change to the graph would result from (1) increasing the
forward-bias voltage (2) increasing the intensity of the radiation (3) increasing the wavelength of
the radiation.
Question 2
Information- An experiment was performed that was similar to Young's double slit experiment. One
image produced is on the attached sheet. This image resulted from green light of wavelength 520 nm
passing through two slits that were separated by 1 mm and then travelled a distance of 80 cm to a screen.
There are various points marked on the image produced where A is the centre of the pattern.
(a) Two students Thelma and Louise discuss the resulting pattern and Thelma declares 'it is all about
waves and path difference, everything in the pattern can be explained in terms of these'. How would
Thelma then explain what is happening at points A, B & C ?
(b) From the values given in the information what would be the actual spacing between adjacent bright
bars?
(c) If a different filter was then used to produce red light of wavelength 650 nm what would happen to
the pattern (and also calculate the new fringe spacing)?
(d) Give two different ways (including actual measurements) that the red light pattern apparatus could
now be changed to match the original fringe spacing of the green light.
(e) The same experiment (as with the original green light) is now conducted using two blue laser diode
lights of wavelength 455 nm which are spaced the same as the original slit separation. How would
the pattern produced compare to the original 'green pattern'? Very briefly justify your answer.
Test
1. The two major experiments you completed were Young's double slit interference and the
photoelectric effect.
(a) If light always behaved as particles how would Young's results have differed?
(b) If light always behaved as wavelike motion how would the results of the photoelectric effect
have differed (only one difference required to be explained)
2.
A beam of X-rays and a beam of electrons both produce a similar diffraction pattern when directed
at a crystal. The X-rays are known to have a wavelength of 2.0 x 10-10 metres.
(a) What can be deduced from the fact that electrons also produce a diffraction pattern.
(b) Find the momentum of the X-rays (include units).
(c) Find the speed of the electrons in m/s.
(d) Find the energy of the X-rays in eV.
(e) Find the energy of the electrons in eV.
3. The energy level diagram for the hydrogen atom is shown
(a) If the atoms are all in the ground state and photons of light with energies of 12.0, 12.4, 12.8,
13.4 and 14.0 eV are passed through the hydrogen, what would you expect to see as an
absorption spectrum. ( briefly explain your answer).
(b) What would you expect to see as an emission spectrum. (briefly explain your answer)
(c) If an electron was in the fourth excited state initially what would be the longest wavelength
photon of light that could be emitted.
VCE Physics Outcome 2
Use wave and photon models to analyse, interpret and explain interactions of light and matter and
quantised energy levels of atoms.
Name
Criteria
Photoelectric Effect Data Analysis
Analyses and interprets experimental results from a photoelectric effect experiment and
explains their significance (DA 1a)
Describes, explains and makes links between qualitative and quantitative concepts for
photoelectric effect. (DA 1d)
Applies ideas and concepts to explanations of new situations. (DA 1 e,f,g)
Applies concepts to analyse information and data to explain relationships. (DA 1b)
Integrates concepts and calculations to reach correct solutions. (DA 1c)
Double Slit Interference Data Analysis
Analyses and interprets experimental results from a double slit interference
experiment and explains their significance (DA 2a)
Describes, explains and makes links between qualitative and quantitative concepts for
double slit interference. (DA 2b)
Applies ideas and concepts to explanations of new situations.
Applies concepts to analyse information and data to explain relationships. Integrates
concepts and calculations to reach correct solutions. (DA 2c,d,e)
Test
Analyses and interprets experimental results and explains their significance. (T 1a,b)
Describes, explains and makes links between qualitative and quantitative concepts. (T 2a)
Applies ideas and concepts to explanations of new situations.(T 3a,b)
Applies concepts to analyse information and data to explain relationships. (T 4a)
Integrates concepts and calculations to reach correct solutions.(T 2b,c,d,e, 3c)