9.4 From
Ideas to Implementation
Contextual outline
By the beginning of the twentieth century, many of the pieces of the physics puzzle seemed to be falling into place. The wave model of light had successfully explained interference, diffraction and the wavelengths at the extremes of the visible spectrum had been estimated. The invention of a pump that would evacuate tubes to 10-4 atmospheres allowed the investigation of cathode rays. X-rays would soon be confirmed as electromagnetic radiation and patterns in the periodic table appeared to be nearly complete. The nature of cathode rays was resolved with the measurement of the charge on the electron soon to follow. There was a small number of experimental observations still unexplained but this, apparently complete, understanding of the world of the atom was about to be challenged.
The exploration of the atom was well and truly inward bound by this time and, as access to greater amounts of energy became available, the journey of physics moved further and further into the study of subatomic particles. Careful observation, analysis, imagination and creativity throughout the early part of the twentieth century developed a more complete picture of the nature of electromagnetic radiation and matter. The journey taken into the world of the atom has not remained isolated in laboratories. The phenomena discovered by physicists have, with increasing speed, been channelled into technologies, such as computers, to which society has ever-increasing access. These technologies have, in turn, often assisted physicists in their search for further knowledge and understanding of natural phenomena at the sub-atomic level.
Outcomes
This module contributes to the following course outcomes:
A student:
H1 evaluates how major advances in scientific understanding and technology have changed the direction or nature of scientific thinking
H2 analyses the ways in which models, theories and laws in physics have been tested and validated
H3 assesses the impact of particular advances in physics on the development of technologies
H4 assesses the impact of applications of physics on society and the environment
H5 identifies possible future directions of research in physics
H8 analyses wave interactions and explains the effects of those interactions
H9 explains the effects of electric, magnetic and gravitational fields
H10 describes the nature of electromagnetic radiation and matter in terms of the particles
H11 justifies the appropriateness of a particular investigation plan
H12 evaluates ways in which accuracy and reliability could be improved in investigations
H13 uses reporting styles and terminology appropriately and successfully to communicate information and understanding
H14 assesses the validity of conclusions drawn from gathered data and information
H15 explains why an investigation is best undertaken individually or by a team
H16 justifies positive values about and attitudes towards both the living and non-living components of the environment, ethical behaviour and a desire for critical evaluation of the consequences of the applications of science.
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1. Increased understandings
of cathode rays led to the development of television |
Students learn to: explain that cathode ray tubes allowed the
manipulation of a stream explain why the apparent inconsistent behaviour of cathode rays caused debate as to whether they were charged particles or electromagnetic waves identify that charged plates produce an electric field describe quantitatively the force acting on a charge moving through a magnetic field
discuss qualitatively
the electric field strength due describe quantitatively the electric field due to oppositely charged parallel plates outline Thomsons
experiment to measure outline the role in a cathode ray tube of: electrodes in the the electric field the fluorescent screen outline applications of cathode rays in oscilloscopes, electron microscopes and television sets discuss the impact of increased understandings of cathode rays and the development of the oscilloscope on experimental physics |
Students: perform an investigation and gather first-hand information to observe the occurrence of different striation patterns for different pressures in discharge tubes perform an investigation and gather first-hand information to demonstrate and identify properties using discharge tubes: containing a maltese cross containing electric plates with a fluorescent display screen containing a glass wheel and analyse the information gathered to determine the charge on the cathode rays solve problem and analyse information using:
and
gather, analyse and process information on the use of
electricallly charged plates and point charges in photocopying machines gather secondary information to identify the use of magnetic fields in television sets |
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2. The reconceptu-alisation
of the model of light led to an understanding of the photoelectric effect and
black body radiation |
Students learn to:
explain qualitatively Hertzs experiments in measuring the speed of radio waves and how they relate to light waves describe Hertzs observation of the effect of a radio wave on a receiver and the photoelectric effect he produced but failed to investigate outline applications of the production of electromagnetic waves by oscillating electric charges in radio antennae identify Plancks hypothesis that radiation emitted and absorbed by the walls of a black body cavity is quantised identify Einsteins contribution to quanta and its relation to black body radiation explain the particle model of light in terms of photons with particular energy and frequency identify the relationships between photon energy, frequency, speed of light and wavelength:
and
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Students: perform an investigation to demonstrate the production and reception of radio waves perform a first-hand investigation to demonstrate the photoelectric effect identify data sources, gather, process and analyse information and use available evidence to assess Einsteins contribution to quanta and their relation to black body radiation identify data sources gather, process and present information to summarise the use of the photoelectric effect in: breathalysers solar cells photocells solve problems and analyse information using:
and
identify data sources, gather and process
information to discuss Einstein and Plancks debate about whether science
research is removed from social and political forces |
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3. Limitations of past technologies and increased research into the structure of the atom resulted in the invention of transistors |
Students learn to:
describe the de Broglie model of electrons in orbits around atoms identify that some electrons in solids are shared between atoms and move freely describe the difference between conductors, insulators and semiconductors in terms of band structures and relative electrical resistance identify absences of electrons in a nearly full band as holes, and recognise that both electrons and holes help to carry current compare qualitatively the relative number of free electrons that can drift from atom to atom in conductors, semiconductors and insulators identify
that the use of germanium in early transistors is related to lack explain why silicon became the preferred raw material for transistors describe how doping a semiconductor can change its electrical properties identify differences in p and n-type semiconductors in terms of the relative number of negative charge carriers and positive holes discuss
differences between solid state and thermionic devices and discuss why solid
state devices replaced thermionic devices |
Students: perform an investigation to model the difference between conductors, insulators and semiconductors in terms of band structures perform an investigation to demonstrate a model for explaining the behaviour of semiconductors, including the creation of a hole or positive charge on the atom that has lost the electron and the movement of electrons and holes in opposite directions when an electric field is applied across the semiconductor gather, process and present secondary information to discuss how shortcomings in available technology lead to an increased knowledge of the properties of materials with particular reference to the invention of the transistor gather, process and analyse secondary information to describe the relationship in solar cells between the photoelectric effect, semiconductors, electric fields and current identify
data sources, gather, process, analyse information and use available evidence
to assess the impact of the invention of transistors on society with
particular reference to their use in microchips and microprocessors |
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4. Investigations into the
electrical properties of particular metals at different temperatures |
Students learn to:
outline
the methods used explain that metals possess a crystal lattice structure identify that the conducting properties of metals are related to the large number of electrons able to drift through their crystal lattice structure discuss why drift velocity is related to: the density of electrons the cross sectional the electronic charge discuss
how the lattice impedes the paths of electrons causing heat identify that superconductors, while still having lattices, allow the electrons to pass through unimpeded with no energy loss at particular temperatures explain current theory that suggests that superconductors are conducting materials that, at specific temperatures, force electrons to pair and, through interactions with the crystal lattice, are ultimately able to form an unimpeded orderly stream discuss the advantages of using superconductors and identify current limitations to their use |
Students: plan,
chose equipment or resources for, and perform process
information to identify some of the metals, metal alloys and compounds that
have been identified as exhibiting the property of superconductivity and the
critical temperatures at perform
an investigation and gather first-hand information to observe magnetic
levitation and the way the magnet is held in position analyse
information gather
and process information to describe gather and process information to discuss possible applications of superconductivity and the effects of those applications on computers, generators and motors and transmission of electricity through power grids process
information to recall the states of matter and their properties and debate
whether superconductivity is a new state |