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Questions and answers on the 'Photoelectric Effect'.

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Introduction

Physics Assessment Task

Part 1

  1. Explain what is meant by the ‘Photoelectric Effect’.

The Photoelectric effect occurs when light falls onto a metal surface and electrons are emitted. This not only depends on the frequency and intensity of light, but also the metal.

Einstein explained this phenomenon by employing the ‘Particle Theory” of light, claiming that there are photons in light, and these are packets of energy. When atoms of an element are irradiated by a light source, the electrons can absorb energy from these photons and move into a higher energy shell. The light must have a minimum frequency or energy for this process to be exhibited. It was found that if light was at, or above, this certain minimum frequency, then the amount of electrons emitted is proportional to the intensity of light.

Later is was found that each metals has a minimum frequency required to release electrons, it was proved that if the light frequency was below this minimum value no electrons would be ejected, no matter how intense the light was. When the frequency was above the minimum electrons would be released and the more intense the light or the more photons the more electrons that were emitted. Also higher frequency EMR displayed this effect the best.

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Middle

Solar energy is a cost-effective and viable option in many remote areas where power companies may charge anywhere from $18,000-$60,000 a kilometre (depending on terrain) to run a power line to an ‘unserviced’ area.

Though solar energy has its limitations

Not all light is used in this process, most of the sunlight energy cannot be used to free electrons in the solar cells, as it is the wrong frequency and either is reflected or passes through without hitting the electrons.

The electricity attained has a very small electrical potential, even with the most efficient solar cells, therefore they must be chained together in large arrays to be effective enough to provide sufficient energy.

It can only be used during sunny days, it is not suitable for cloudy climates and start up costs are uneconomical.

At the moment solar energy supplies less than 1% of the worlds energy.

Then the most obvious question. What happens when the sun is not shinning?

Though they need to be able to compete with utilities, research is still going on to bring the price of these down though it wont happen for a while yet.

Part of the problem is that manufacturing needs to be done on a large scale to reduce costs as much as possible.

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Conclusion

Despite all this there has been tests in Denmark of Superconductor transmission lines, and there are plans for the future. In May of 2001 150,000 residents of Copenhagen, Denmark, received their electricity through HTS (high-temperature superconducting) material. That cable was only 30 meters long, but proved adequate for testing purposes.

More efficient electrical generators can be manufactured if superconducting wire is used rather than the conventional copper wire. If superconducting wire was made into loops, when large currents flow a powerful electromagnet would be set up that would be very effective in a motor or generator as long as it stays below its critical temperature. The efficiently would be well above 99% and their size would half that of normal generators.

Electronic Switches

Fast computers rely of switching between current highways using transistors made from semiconductors. Superconducting devices can be designed to pass a fixed current with barley any driving voltage. The idea is to manufacture computers that are up to 200 times faster than conventional high-speed computers.

The problem of cooling these devices to their critical temperature still exist, and higher temperature superconductors need to be found that are more suited to their applications. The ideal superconductor would need to be ductile, have a critical temperature much higher than the current and arechemically stable in a variety of environments.

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