Dos cargas puntuales están fijas en el eje x: q1 = –3.0 µC esta en el origen, O, con x1 = 0.0 cm, y q2 =6.0 µC está situada en el punto A, con x2 = 8.0 cm. Donde debería colocarse una tercera carga, q3, sobre el eje x, de modo que
la fuerza electrostática total que actúa sobre esta sea cero? (0.25)
a) 27 cm
b) 0 cm
c) 8.0 cm
d) –27 cm

With the simplified model of the eye, what corrective lens (specified by focal length as measured in air) would be needed to enable a person underwater to focus an infinitely distant object? (be careful-the focal length of a lens underwater is not the same as in air! assume that the corrective lens has a refractive index of 1.62 and that the lens is used in eyeglasses, not goggles, so there is water on both sides of the lens. assume that the eyeglasses are 1.90