Rays of light incident on a lens and parallel to the principal axis of the lens converge

a. at the focal point of the lens.
b. in front of the lens.
c. in back of the lens.
d. at the center of curvature of the lens.

What is the energy of a photon of ultraviolet radiation with a frequency of 4.4 × 1015 hz? planck’s constant is 6.63 × 10–34

What is a good example of instantaneous speed

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.