Lens Flashcards
What is a lens
A lens is a transparent refracting medium bound by either two refracting surfaces or one refracting surface and one plane surface
Ways to identify convex lens
Thick in middle, thin at periphery. Lens bulges out in the middle and light gets converged
Three types of convex lens
Bi convex
Plano Convex
Concave convex
Ways to identify concave lens
Thick at periphery, thin in middle, bent inwards, light diverges or appears to diverge
Types of concave lens
Bi concave
plano concave
convexo concave
Define centre of curvature
Centre of the sphere whose part is in the lens surface
Define radius of curvature
Radius of the sphere whose part is the lens surface
What is principal axis
It is the line joining the centre of curvature of two surfaces of the lens
What is principal axis
It is the line joining the centre of curvature of two surfaces of the lens
Define optical centre
It is a point on the principal axis such that a ray of light directed towards this point emerges parallel to its direction of incidence
What is the first focal point for a convex lens?
Point on principal axis such that a light emerging from that point, after refraction thru the lens become parallel to principal axis
What is the first focal point for a concave lens
Point on principal axis such that the incident rays of light appearing to meet at it, after refraction from lens become parallel to principle axis
What is the second focal point of a convex lens
Point on principal axis such that the rays of light incident parallel to the principal axis, after refraction pass through it
What is the second focal point of a concave lens
Point on the principal axis such that rays of light parallel to principal axis, after refraction appear to diverge from this point
Define : Focal plane
first focal plane
second focal plain
Focal plane is a plane normal to the principal axis passing through the focus
First focal plane is the plane passing through the first focal point and normal to the principal axis
Second focal plane is the plane passing through the second focal point and is normal to the principal axis
Define focal length
first focal length
second focal length
distance of focus from optical centre is focal length
distance from optical centre to its first focal point is first focal length
distance from optical centre to its second focal point is second focal length
What 2 factors does focal length depend on and how is it affected by them?
- R.I of lens w respect to surrounding medium. Inc in R.I = Inc in Focal length
- Radii of curvature. Thicker the lens less the focal length
when obj is at infinity
Real, inverted, point sized, image formed at f2
Used in burning glass
What lens is used in cameras ? State its nature and position
When the lens is beyond 2F1
image is real inverted and highly diminished
What distance is the object at from the lens of a terrestrial telescope? State the nature of the image
Object is at 2F1
real inverted same size as obj
What distance is the object at from the lens of a slide projector? State the nature of the image
Between 2F1 and F1
real, inverted and magnified
What distance is the object at from the lens of a collimator of a spectrometer? State the nature of the image
Object is at F1
real, inverted , highly magnified
What distance is the object at from the lens of a reading lens
Between F1 and Optical centre
virtual, erect, magnified
What distance is the object at from the lens of a galilean telescope? State the nature of the image
Obj at infinity
virtual, erect, point sized
What distance is the object at from the lens of spectacles for myopic eye? State the nature of the image
Obj at finite distance from concave lens
virtual, erect, diminished
