If a 20 W laser beam, which has an initial diameter of 2.0 mm, spreads out to a diameter of 2.0 m after traveling 10,000 m, what is the initial intensity of the beam?
a.
b.
c.
d.
e.
b.
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High-mass stars become ________ variables when they cross the instability strip, while low-mass stars become ________ variables.
A. RR Lyrae; Cepheid B. T Tauri; Cepheid C. Cepheid; RR Lyrae D. Cepheid; T Tauri E. ZZ Ceti; RR Lyrae
As measured from the Earth, a spacecraft is moving at speed 0.80c when it releases a probe at speed 0.60c relative to the spacecraft in a forward direction. What would be the speed of the probe as measured from the Earth?
a. 0.70c b. 0.81c c. c d. 0.95c
A gas is placed in a thermally insulated container as shown below
As the piston is slowly raised...
Of the following substances, which one contains the highest density of free electrons?
a. glass c. iron b. hard rubber d. amber