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.

Physics & Space Science

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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

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Physics & Space Science

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

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Physics & Space Science

A gas is placed in a thermally insulated container as shown below

As the piston is slowly raised...

1.... the gas gives off heat to the environment (Q<0). 2.... the gas absorbs heat from the environment (Q>0). 3.... the gas does not exchange any heat with the environment (Q=0). 4.The heat exchanged with the environment cannot be determined.

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Physics & Space Science

Of the following substances, which one contains the highest density of free electrons?

a. glass c. iron b. hard rubber d. amber

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Physics & Space Science