You are designing eyeglasses for someone whose near point is 60 cm. What focal length lens should you prescribe so that an object can be clearly seen when placed at 25 cm in front of the eye?
a. ?18 cm
b. 18 cm
c. 43 cm
d. 60 cm
e. –43 cm
c
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Waves on a String: A string of mass m is under tension, and the speed of a wave in the string is v. What will be the speed of a wave in the string if the mass of the string is increased to 2m but with no change in the length or tension?
A. v/2
B. v/
C. v
D. 2v
E. 4v
Elements heavier than hydrogen and helium constitute about ________ of the mass of the interstellar medium
A) 0.002% B) 2% C) 70% D) 98%
As a gust of wind blows across a field of grain, a wave can be seen to move across the field as the tops of the plants sway back and forth. This wave is a:
a. transverse wave. b. longitudinal wave. c. polarized wave. d. interference of waves.
The index of refraction of a substance is
a)equal to the speed of light in vacuum divided by its speed in that substance. b)equal to the speed of light in that substance. c)the same as the angle of refraction. d)the same as the angle of incidence. ? ? ?