what will be the value if in the formula refraction due to spherical surfaces R is infinity
Answers
Answer:
Formula for refraction of light from spherical surface is
v
n
2
−
u
n
1
=
R
n
2
−n
1
where OB=−u,OI=+v,BC=+R
n
2
is refractive index of medium 2 i.e. spherical glass
and n
1
is refractive index of medium 1.
Figure (a) shows the geometry of image formation by a double convex lens. the image formation can be seen in two steps, the first refracting surface form an image I
1
which act as an virtual object for the second surface. applying the equation above written for surface 1
OB
n
1
+
BI
1
n
2
=
BC
2
n
2
−n
1
similarly form second interface
−
DI
1
n
2
+
DI
n
1
=
DC
2
n
2
−n
1
(refractive index of right side medium is n
1
and for left side medium is n
2
, and also DI
1
is negative.)
now for thin lens BI
1
=DI
1
. adding both the equations we get
OB
n
1
+
DI
n
1
=(n
2
−n
1
)(
BC
1
1
+
DC
2
1
)
and assuming the object at infinity means OB will be very large
we get
DI
n
1
=(n
2
−n
1
)(
BC
1
1
+
DC
2
1
)
and dividing both sides with n
1
DI
1
=(n
21
−1)(
BC
1
1
+
DC
2
1
)
replacing DI=f,BC
1
=+R
1
,DC
2
=−R
2
FINALLY we get
f
1
=(n
21
−1)(
R
1
1
+
R
2
1
).
this equatuation is known as lenz makers formula