A teacher sets up the stand carrying a convex lens of focal length 15 cm at 42.7 cm mark on the optical bench. He asks four students A, B, C and D to suggest the position of screen on the optical bench so that a distinct image of a distant tree is obtained immediately on it. The positions suggested by the students were as:
(A) 12.7 cm
(B) 29.7 cm
(C) 57.7 cm
(D) 72.7 cm
The correct position of the screen was suggested by:
A
B
C
D
(3)
Focal length of convex lens
It is placed at 42.7 cm mark on optical bench.
When we want the distant objects to be focused, we get image at focus of convex lens.
Because rays from distant object are parallel rays and they get converged at focus.
A student has traced the path of a ray of light through a glass slab as follows. If you are asked to label 1, 2, 3 and 4, the correct sequencing of labeling ∠i, ∠e, ∠r and lateral displacement respectively is :
2, 1, 3, 4
1, 2, 3, 4
1, 3, 2, 4
1, 3, 4, 2
(3)
Here 1 is angle of incidence, 3 is angle of emergence, 2 is the angle of refraction and 4 is the lateral displacement.
In an experiment to trace the path of a ray of light through a triangular glass prism, a student would observe that the emergent ray :
is parallel to the incident ray.
is along the same direction of incident ray.
gets deviated and bends towards the thinner part of the prism.
gets deviated and bends towards the thicker part (base) of the prism.
(4)
Student will observe that the emergent ray gets deviated and bends towards the thick parts (i.e., base) of the prism.
Focal length of plane mirror is:
at infinity
zero
negative
None of these
(1)
A plane mirror is a flat, reflecting surface. Thus, in case of plane mirror, when the parallel rays of light strike the mirror they get reflected back parallel to each other. So, they never meet, so we can say that they meet at infinity. So, the focal length of the plane mirror is infinity.
