decreasing power?

[donaldduck]

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decreasing power input to a light bulb causes its brightness to decrease. How does the color of the emitted light change?

A. the emitted spectrum shifts to longer wavelengths
B. the spectrum does not change

the answer is A...why?

 

[bullsfan1986]

Use these two formulas: 1) Energy/time= Power and 2) Energy= hc/wavelength . If you decrease your power over a constant time your energy decreases. So if your energy decreases and you know that h and c are constant, your wavelength will have to increase. Hope this helps.

 

[ilovemcat]

decreasing power input to a light bulb causes its brightness to decrease. How does the color of the emitted light change?

A. the emitted spectrum shifts to longer wavelengths
B. the spectrum does not change

the answer is A...why?

Power = (I^2)(R) = Work(Energy)/time

In order for power to decrease during a time interval, the amount of energy emitted needs to decrease.

Energy = hf ==or==> hc/(wavelength)

Because energy and wavelength are inversely proportional, reducing the amount of energy (by decreasing power), results in an increase of wavelength.

 

[donaldduck]

thanks guys! looks like my knowledge in this area is weaker than i had originally thought...when i looked at the answer i couldnt begin to reason why A was the correct answer... but ur explanations make perfect sense! well its back to studying!