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The energy of a photon depends on its _________ .

In the Doppler effect, a red shift of spectral lines shows us the source is receding from us.

Galileo’s observations of the entire phase cycle of Venus proved that Ptolemy’s epicycles could not be correct in keeping Venus between us and the Sun.

In electromagnetic waves, the electric and magnetic fields vibrate__________ to each other.

When Earth overtakes Mars, the outer planet retrogrades near __________ .

According to Newton’s third law, when the Voyager probes passed Jupiter in 1979, they exerted exactly the same force on Jupiter as the giant planet did on them.

An emission line results from an electron falling from a higher to lower energy orbital around its atomic nucleus.

Which of these is not a form of electromagnetic radiation?

The Doppler effect can reveal the rotation speed of a star by the splitting of the spectral lines.

An electron has a(n)  _________ electric charge.