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Blackbody Spectrum Lab

1. i) The approximate surface temperature of the star that exhibits peak power spectrum at the border between red and the infrared light, is found to be 4080 K from the simulation. The corresponding temperature in °C is equal to 3806.85° Celsius.

ii) The approximate surface temperature of the star that exhibits peak power spectrum at the border between blue and the ultraviolet light, is found to be 6990 K from the simulation. The corresponding temperature in °C is equal to 6716.85° Celsius.

2. i) Light bulb operating temperature is 2500° C. The wavelength of a light bulb that emits the highest power at the operating temperature of 2500° C is found from the simulation as 1160 nm.

ii) The simulation shows that at 2500° C, the operating temperature of the regular incandescent bulb, the peak power occurs at a wavelength far beyond the visible light spectrum. Evidently, most of the power that the regular incandescent bulb consumes is wasted in the form of invisible light. It can be seen from the simulation that about 10-15% of the spectrum at 2500° C lies in the visible light wavelength, which produces visible light. Therefore, the regular incandescent bulbs are highly energy inefficient.

3. The power emission will be increased at a wavelength of 1000 nm if the temperature goes on decreasing. It will never increase with the decreasing temperature. The simulation shows that with the reduction in the temperature scale, the graph flattens indicating the relative loss in power intensity.

 

If the temperature of an object goes on decreasing, the total amount of power that the object emits will also decease always. We know that the power emission of an object varies directly with the fourth power of the temperature. Therefore, the decrease in temperature would be realized in the reduced power emission.

 

Since the power emitted by an object is directly proportional to its surface area, an enlargement of the surface area of a bulb filament would exhibit its result in larger power radiation as IR. However, since all the wavelength would experience similar power increase, the fraction of IR power radiation would remain the same.

4. i) The reduction in the temperature exhibits in the reduction of power as the height of the curve lowers in the simulation. Therefore, a less-than-unity ratio is expected at 500nm for temperature reduction from 2500° C to 2000° C. With the help of the ruler, the height of the curve at 500nm at 2500° C and 2000° C are found to be 11 cm and 1.1 cm, which gives a ratio of 1.1/11 or 0.1.

ii) The peak wavelength for the bulb operating at a temperature of 2000° C is found to 1280 nm approximately.

 

5. i) The electromagnetic radiation emitted by the solar spectrum spreads over ultraviolet, visible and infrared region. Not all the radiations from sun are visible. The peak power occurs near the blue and ultraviolet region, which implies that there is more blue light in solar spectrum than the red.

ii) Since solar spectrum is a blend of EM wave at different wavelengths, the solar radiation contains multiple wavelengths rather than one.

iii) The temperature of the sun directly affects the distribution of power. The more the temperature the more is the radiation and less temperature gives less power radiation. On the other hand, the increase in temperature shifts the peak power point of the graph towards right.