Question Video: Analyzing Light Spectra Plotted on a Graph | Nagwa Question Video: Analyzing Light Spectra Plotted on a Graph | Nagwa

Question Video: Analyzing Light Spectra Plotted on a Graph Physics • Third Year of Secondary School

The lines shown in the following graph represent the spectra of light emitted by two objects. Which line represents the object that emits a greater range of wavelengths? [A] The red solid line [B] The green dashed line [C] The range of wavelengths is the same for both lines

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Video Transcript

The lines shown in the following graph represent the spectra of light emitted by two objects. Which line represents the object that emits a greater range of wavelengths? (A) The red solid line, (B) the green dashed line, (C) the range of wavelengths is the same for both lines.

Let’s look for a moment at these two spectra on our graph. The axes of our graph indicate light intensity against light wavelength. There are no specific values labeled. But just to get a sense, if we were to pick a point at random along our green dashed line, say this point right here, that point is telling us that at this wavelength, whatever that wavelength is, the object giving off light, that’s represented by the green dashed line, is emitting light at this intensity, whatever that intensity is.

Our question asks us to figure out which object emits light over a greater range of wavelengths. If we look first at the range of wavelengths given off by the object whose light corresponds to the red solid line, we see that range begins roughly here, and it ends roughly here. Outside of this wavelength range, this object is emitting essentially no light, light of intensity zero.

Notice that the range of wavelengths of light for the green dashed line includes this range and it also extends past it a little bit at either end. The green dashed line shows emission of light at all the wavelengths of the red solid line and then some additional wavelengths, for example, this wavelength here where there’s a nonzero intensity of the green dashed line. And this tells us how to answer our question. Because the green dashed line has a nonzero intensity over a greater range of wavelengths, this is the one corresponding to the object that emits light over a greater range of wavelengths.

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