How do astronomers measure the temperature of stars?

A. The inverse square law is used.
B. By comparing the star's absolute and apparent brightness.
C. The rate of change of the color of the star is measured.
D. By looking at which absorption lines are present in the star's spectrum.
E. Temperature is determined from the radius of the star that is measured by radar.


Answer: D. By looking at which absorption lines are present in the star's spectrum.

Physics & Space Science

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Initially, an inductor with no resistance carries a constant current. Then the current is brought to a new constant value twice as large. After this change, when the current is constant at its higher value, what has happened to the emf in the inductor?

1.It is larger than before the change by a factor of 4. 2.It is larger by a factor of 2. 3.It has the same nonzero value. 4.It continues to be zero. 5.It has decreased.

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What is meant by the Astronomical Unit?

What will be an ideal response?

Physics & Space Science

Which one of the following scientists first built and operated devices that could emit and detect human-made electromagnetic radiation?

a. Hertz b. Ampere c. Maxwell d. Lenz

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If vector = -3.0 - 4.0 , and vector = +3.0 -8.0 , then the magnitude of vector = - is

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Physics & Space Science