Question: The intensity of a light source with power P on a circular surface of radius r placed at a certain distance is \. Where \ is the intensity, P is the power and A is the area of cross section.Įxample: What is the intensity of light incident normal to a circular surface of radius 5 cm from a 100 W source of light? Intensity will depend on the strength and amplitude of a wave. It is generally measured with units of watts per square metre (i.e., Wm–2). It is the quantity of energy the wave –conveys per unit time over unit area. ↳ Is this connected to that? Use a homemade electronic tester to find out if electricity can flow between two objects.Intensity is a measure of the energy transmitted by a wave.↳ Investigating the 'Mpemba Effect': Can Hot Water Freeze Faster than Cold Water?.↳ From Dull to Dazzling: Using Pennies to Test How pH Affects Copper Corrosion.↳ Forensic Science: Building Your Own Tool for Identifying DNA.↳ Electrolyte Challenge: Orange Juice vs.↳ Do Oranges Lose or Gain Vitamin C After Being Picked?.↳ Math & Computer Science Sponsored by Hyperion Solutions Corp.↳ Grades 9-12: Getting Ready for the Science Fair.↳ Grades 6-8: Getting Ready for the Science Fair.↳ Grades K-5: Getting Ready for the Science Fair.↳ Science Teachers: Fairs, Projects, and General Support.↳ Advanced Science Competitions (Intel ISEF, Intel STS, Siemens Competition, JSHS, etc.).↳ Grades 9-12: Math and Computer Science.↳ Grades 9-12: Life, Earth, and Social Sciences.↳ Grades 6-8: Math and Computer Science.↳ Grades 6-8: Life, Earth, and Social Sciences.↳ Grades K-5: Math and Computer Science. ↳ Grades K-5: Life, Earth, and Social Sciences.Active Forums (Make all new posts here).It's important not to get this equation mixed up with the inverse square law, which describes how light intensity changes with distance from the source. The purpose of this equation is to convert resistance (what you are actually measuring) to lux (the unit of light measurement). The plane of the interface (y0) T is perpendicular to this page. I R y Here, the plane of incidence (z0) is the x z plane of the diagram. If you bought a different photoresistor, you would need to look at its datasheet to get the slope and intercept of the line. S polarization is the perpendicular polarization, and it sticks up out of the plane of incidence. To be clear, the numbers 375.81 and 1.084 are specific to this photoresistor. But it would also be valid to write the equation as So the slope of the line is negative 1.084, we can write that as 1/R^1.084 instead of R^(-1.084). Trying to put that in words: x to a negative number is equal to one over x to that number. The last part is also a bit of algebra your grandson may or may not have seen yet: The y-intercept of the line is 375.81, and the slope of the line is -1.084. Where a is the y-intercept of the line and k is the slope of the line (for more information and some examples, see this page ). Be careful - the x-axis is values of 1/d 2. The equation for a straight line on a log-log plot is The relationship between light intensity - at these low light intensities is linear. Again, depending on what grade your grandson is in, he might not have encountered logarithms in math class yet. A plot with logarithmic scales for both axes is called a log-log plot for short. (2015), P (1 O 2/O 0)P, with a maximum rate constant P, with a maximum rate constant P 0 and initial oxygen concentration Y 0. they go 1, 10, 100 instead of 10, 20, 30.). where b 83.6aqw, w being the UV light wavelength (in cm) and light intensity I(z,t) in mW/cm 2 q is the quantum yield of the PS triplet state Equation (11) also includes an oxygen source term given by Semchishen et al. However, if you look at the graph on the datasheet you will see that it has a logarithmic scale on both axes (e.g. The equation is derived from the graph labeled "Typical Resistance vs Variable Illumination" on the photoresistor's datasheet:ĭepending on what grade your grandson is in, he is probably familiar with the equation for a line (usually expressed as y = m*x + b) on a graph with linear axes. In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function. Here's the more detailed explanation from our email: Asim Kumar Roy Choudhury, in Principles of Colour and Appearance Measurement, 2014. In case you didn't see it yet, there is a very brief explanation of this equation on the "Make it Your Own" tab of the project: Pasting the full reply here so others can see it as well. We sent the following message as a reply to your email - please let us know if that email didn't go through (if so, we apologize).
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