Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?
A) spectroscopic binary
B) eclipsing binary
C) visual binary
D) double star
A) spectroscopic binary
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A magnetic compass points towards the north geographic pole of the Earth because
A. there is a south magnetic pole near the north geographic pole. B. there is a north magnetic pole near the north geographic pole. C. all magnetic poles, north or south, point that way due to the spin of the Earth. D. the static electricity in the atmosphere causes the alignment of the compass.
Experts are absolutely sure that there is danger to the health of people living underneath power transmission lines
What will be an ideal response?
An astronaut is taking a space walk when his tether breaks. He has a big drill. How can he get back to the space ship?
A. Turn his back to the ship and throw the drill forward B. Face the ship and throw the drill forward. C. Throw the drill towards the tether.
A concave mirror has a focal length of 20 cm. What is the position (in cm) of the resulting image if the image is inverted and four times smaller than the object?
a. 15 b. 25 c. 50 d. 100 e. -15