SUBJECT and GRADE Physical Sciences Gr 12
TERM 3 Week 4
TOPIC Optical Phenomena and Properties of Materials (This section must be read in conjunction with the CAPS, p.
132–133.)
AIMS OF LESSONS Photo-electric effect
• Perform calculations using the photoelectric equation with graphs:
E =Wo+ EKmax, where E = hf and Wo= hfo and EKmax = ½mv2max
• Explain the effect of intensity and frequency on the photoelectric effect.
Emission and absorption spectra
• Explain the formation of atomic spectra by referring to energy transition.
• Explain the difference between atomic absorption spectra and atomic emission spectra.
An atomic absorption spectrum is formed when certain frequencies of electromagnetic
radiation that passes through a medium, e.g. a cold gas, is absorbed.
An atomic emission spectrum is formed when certain frequencies of electromagnetic
radiation are emitted due to an atom's electrons making a transition from a high-energy
state to a lower energy state.
, RESOURCES Paper based resources Digital resources
You are referred to the: Refer to the relevant digital resources:
• Optical Phenomena topic and • https://wcedeportal.co.za
Emission and Absorption Spectra • HeyScience App for Physical Sciences
topic in the textbook or study guides • Past NSC Examination papers
that you will have on hand. • You Tube videos
• Examination Guideline (page 13)
• Mind the Gap books (pages 142 - Calculations on Photo electric effect
147) https://youtu.be/253wCijyZJo
• Past NSC Examination papers (refer Atomic Absorption Spectroscopy
to Paper 1) https://youtu.be/YDh4EjyDmjc
An explanation of how Atomic Absorption Spectrum is formed
https://youtu.be/GO5KKAZoqeE
Bohr Model to explain Emission Spectra
https://youtu.be/sAPEAXQT9_Q
Emission and Absorption Spectra
https://youtu.be/1uPyq63aRvg
INTRODUCTION Part 1
1. You should be able to explain how a change in frequency or intensity affects the energy of an ejected
photo-electron.
An increase in frequency, increases the energy of the photons only (increases the kinetic energy of the
photoelectrons) and not the number of photoelectrons. The work function of the metal is constant and
therefore the kinetic energy of the ejected electron increases.
An increase in intensity means that (for the same frequency) the number of photons per second
increases but the energy of the photons stays the same. The work function of the metal is constant and
therefore the kinetic energy of the ejected electron remains the same.
2. Observe the following youtube videos on calculations on Photo electric effect
https://youtu.be/253wCijyZJo
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