Diffraction of Light 6. Mirrors 7. Lenses 8. Optical Equipments 9. Light as Electromagnetic Waves. Literature. Lepil. O., Kupka, Z.: Fyzika pro gymnázia – Optika. Lepil. O., Kupka, Z.: Fyzika pro gymnázia – Optika, ; SVOBODA, Emanuel. Přehled středoškolské fyziky. 4. uprav. vyd. Praha: Prometheus, s. Fyzika pro gymnázia: fyzika mikrosvěta. 3., přeprac. vyd. Praha: Prometheus, s. ISBN info; LEPIL, Oldřich. Fyzika pro gymnázia: optika.

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This paper presents ideas for experiments and projects measuring illumination with a luxmeter. The activities are suitable for basic and secondary school pupils. The main purpose of photometry is to measure visible radiation in a manner that corresponds to human eye perception.

To gain such results, one has to consider the physical properties of light stimuli as well as ldpil basic characteristics of eyesight. The most common task of photometry is to measure illuminance in luxes. The intensity of illumination — illuminance — is measured by a luxmeter. A common luxmeter consists of the measuring device itself and a sensor.

Fyzika pro gymnázia. Optika

The sensor is made of selenium or silicon photocells. Lepl schematic sketch of a gate photocell can be seen in fig. Such a photocell is not yet suitable for measuring illuminance since it does not fulfil the most significant requirement — its spectral sensitivity is different from human eye.

Comparison of photocell and human eye sensitivity can be seen in fig. A luxmeter that does not have an eye correction should not be used for measurements of this type [1].

Special attention should also be paid to another part of a luxmeter — the cosine adapter. A photocell without a cosine adapter would produce measurement error proportional to the angle of incidence of the light [1].


Comparison of photocell and eye sensitivity.

Vl – Eye spectral sensitivity [1]. There are a lot of interesting experiments that can be performed with a luxmeter in a classroom. These experiments can be split into two groups [2, 3]:.

From the dependencies in fig. From the graphs in fig. This equation is sometimes called the photometric law. Good light quality and appropriate illuminance are a necessary requirement for safe work ldpil leisure time.

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Table 1 shows a selection of illuminance standards E for school interiors. The standard values are meant as reference values [5] for horizontal workplace surfaces at a height of 0,85 m above the floor [1, 5]. Professional measurements of illuminance daylight, artificial and combined in workplaces are offered by some state institutions, e. The requirements and standards for illuminance measurements leoil given by the Slovak health ministry [6] and government [7].

Because illuminance is a very important part of a healthy environment and professional measurement methods are not suitable for classroom use, it is useful to perform simple experiments with a luxmeter at different spots at school.

Is the illuminance in our environment good and healthy? This question has strong motivational potential for students. Compare your measured values to the values given by government standards EN Suggest changes that could be made in the case of significant differences. Estimate the illuminance in both workplaces and resting places. Figures 7 and 8 show the measurement results in a classroom, while figures 9 and 10 are results from a laboratory.

The letter L marks each row of desks in the classroom. The classroom is facing towards the west. Windows are at the side belonging to the back row of the graph.

The laboratory is a corner room facing north. There are two windows on the back wall and one on the side wall. The measurements took place at lwpil AM.


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Dependence of desk illuminance E on its placement inside a classroom: L — desk row. From the measured values in figures 7 and 8 it can be concluded that the classroom fulfils the standards only when we turn on the artificial lights. Dependence of desk illuminance E on its placement inside a laboratory: From these results as well as from further experiments studying illuminance in different conditions like weather, season, different times of day, etc.

In the case of illuminance values that do not fulfil standards, let the pupils start a discussion about the reasons for the improper light conditions.

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opptika They will suggest possible solutions to improve the situation. Illuminance in my working place, influence of a lampshade on illuminance, illuminance at your home, illuminance at school, the dependence of illuminance on time after a fluorescent light has been turned on, comparison of classic and power-saving light sources, light in outdoor places.

Further information on these suggestions, such as motivations, question setup, measurement results, and more can be found at this address http: School experiments with a luxmeter.

Physics Teachers’ Inventions Opitka proceedings. Volume Fair 12, Praha Equipment Special equipment Computer aided experiments. Luxmeter The main purpose of photometry is to measure visible radiation in a manner that corresponds to human eye perception.

Types of cosine adapters [1].