Author Question: Two very thin lenses, each with focal length 20. cm, are placed in contact. What is the focal length ... (Read 87 times)

Mimi · **on:** Jul 27, 2018

Two very thin lenses, each with focal length 20. cm, are placed in contact. What is the focal length of this compound lens?

A) 15. cm
B) 10. cm
C) 30. cm
D) 40. cm
E) 20. cm

Question 2

How much energy is carried by a photon of wavelength 660. nm?

A) 1.46 10-48 J
B) 3.01 10-19 J
C) 6.63 10-34 J
D) 5.39 eV
E) 4.78 10-19 eV