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# Construction resources.

Extracts from this document...

Introduction

Construction resources make use of physics in many of their products. Two that I have picked are solar collectors and their use of insutation.

Insulators have the purpose of preventing conduction, convection and radiation to unwanted areas. There are a wide range of techniques and materials used in doing this and I am going to look in depth at this idea.

The company uses solar collectors in many different ways, their main purpose is to collect solar energy and heat energy. They can be used to heat and power many different appliances.

Photovoltaic cells:

Photovoltaic cells transfer the energy carried by the electromagnetic waves that make up sunlight directly to an electrical circuit in order to make a current flow.Light excites electrons to move from one layer to another through semi conductive silicon materials. Only a fraction of a volt is produced so a large array is needed to produce appreciable currents, usually about 20W to 100W. The Photovoltaic cells produce DC current so if alternate current AC is desired then an inverter is required. AC form is commonly available from the mains.

Solar cells:

## Sunlight may also be used to heat water directly.

Middle

Conduction, where heat energy is transferred through solid materials, metals are normally the best conductors. There are a number of factors that affect thermal conductivity. Increasing the area of the cross-section of the solid through which hear flows increases the rate of flow, however increasing the thickness of the wall decreases the flow of heat. Provided that a steady state has been reached (where the temperature of any point is not changing through time) then the rate of flow of heat ΔQ/Δt is given by:

ΔQ/Δt --> A ΔT/Δx

Besides the physical dimensions of the materials, another factor affecting rate of flow is the properties of the material, the Thermal Conductivity of the materials λ through which the heat energy is travelling is the constant of proportionality in this relationship, so:

ΔQ/Δt = -λA ΔT/Δx

The units for thermal conductivity are watts per metre per kelvin.

Conclusion

Bibliography:

## Microsoft Encarta

Strengths and Limitations of Photovoltaic cells:

Since one photovoltaic cell only produces a small fraction of a volt, large arrays are required to produce appreciable voltages. This requires a lot of space and the cells need to be in a place where no shadows will be cast on them. This limits what they can be used for. Also the amount of power produced by the photovoltaic cells directly depends on the amount of sunlight, so they cannot be relied on to produce power for something that constantly needs it. The only way this can be overcome is if some power was stored for a rainy day. But this again would take up space. Also an array of solar collector will be expensive and have a long ‘pay back’ time. However it is environmentally friendly and after the pay back time, savings can be made. Also photovoltaic cells can be made look attractive depending on where they are placed.

Strengths and Limitations of solar cells:

The solar cells have similar limitations to the photovoltaic cells in regards to positioning and cost but a small array is only required to produce enough hot water for something like residential showers or central heating. This is economical and environmentally friendly and solar cells are quite versatile.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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