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Author Question: A zoom lens is adjusted to change its focal length from 38 mm to 304 mm. If the same amount of light ... (Read 34 times)

vinney12

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on: Jul 29, 2018
A zoom lens is adjusted to change its focal length from 38 mm to 304 mm. If the same amount of light is to be admitted to the lens, what is the final f-number if the original f-number was 2.0?
 
  What will be an ideal response?

Question 2

The magnitude of the Poynting vector of a planar electromagnetic wave has an average value of 0.939 W/m2. The wave is incident upon a rectangular area, 1.5 m by 2.0 m, at right angles.
 
  How much total electromagnetic energy falls on the area during 1.0 minute? (c = 3.0 x 108 m/s, 0 = 4  10-7 T  m/A, 0 = 8.85  10-12 C2/N  m2)
  A) 170 J
  B) 210 J
  C) 250 J
  D) 300 J
  E) 340 J


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bblaney

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Reply #1 on: Jul 29, 2018
Answer to Question 1

16

Answer to Question 2

A


vinney12

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Reply 2 on: Jul 29, 2018
Great answer, keep it coming :)

frankwu0507

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Reply 3 on: Yesterday
Excellent

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