In a concave lens, a ray of light emanating from the object parallel to the principal axis of the lens, after refraction:
A
emerges parallel to the principal axis.
B
appears to diverge from the first principal focus.
C
passes through 2F, which is the radius of curvature of the lens.
D
passes through the second principal focus.
The answer is B.
Solution
A concave (diverging) lens makes a ray parallel to the principal axis diverge after refraction, so that it appears to come from the focus on the same side as the object.
By NCERT's convention, the focus on the side of the source of light is called the first focal point ($F_1$), and the other is the second focal point ($F_2$). On this basis the answer is: the ray appears to diverge from the first principal focus.
Note: ALLEN marks this answer as per NCERT but states that conceptually the question should be treated as bonus, because by the standard definition of foci the diverging ray appears to come from the second principal focus.
Ray Optics and Optical Instruments in past papers
89 questions from this chapter have appeared across 25 exam years.
