A zoom lens is adjusted to change its focal length from 38 mm to ...

[vinney12]

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

[bblaney]

Answer to Question 1

16

Answer to Question 2

A

[vinney12]

Thanks for the timely response, appreciate it

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TYSM