Two stars P and Q have slightly different surface temperatures T P and T Q , with T P T Q . Both stars are receding from the earth with speeds v P and v Q relative to the earth. The wave

Question

Two stars P and Q have slightly different surface temperatures T P ​ and T Q ​ , with T P ​ > T Q ​ . Both stars are receding from the earth with speeds v P ​ and v Q ​ relative to the earth. The wavelength of light at which they radiate maximum energy is found to be the same for both:

TestHub · Accepted Answer

By Wien\'s law λ m ​ ∝ 1/ T , so the hotter star P has the shorter intrinsic λ m ​ . Both are observed at the same wavelength, so P must be red-shifted more, which needs a larger receding speed: v P ​ > v Q ​ .

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