It is a PPT on Atmospheric Refraction for the students of Class X.

1. ATMOSPHERIC REFRACTION
Made By: Qhudwa SarmadX.B
R.I.S.Y

2. Content
 What is Refraction?
 Laws of Refraction
 Advanced sunrise and delayed sunset
 Twinkling of stars
 Why don’t planets twinkle
 Apparent flattening of sun’s disc at
sunrise and sunset
 Mirage
 References

3. What is Refraction of Light?
 Refraction of Light is the phenomenon
of change in the path of light, when it
travels from one medium to another.
 The basic cause of Refraction is
change in velocityfrom one medium to
other.

4. Laws of Refraction
 The incident ray, refracted ray and the
normal to the interface at the point of
incidence, all lie in the same plane.
 The product of refractive index and
sine of angle of incidence/refraction at
a point in a medium is constant
 i.e., u * sin i= constant. therefore, u1 sin
i1 = u2 sin i2 i1 = i and i2 = r hence, u2 /
u1 = sin i / sin r and it is also known as
SNELL’s LAW.

5. Atmospheric Refraction

6. Advanced Sunrise and Delayed
Sunset The sun is visible to us
before the actual
sunrise and after the
sunset.
 The density of air near
the surface of earth is
slightly higher.
 The rays from the sun
coming through space
enter at the top of
earth’s atmosphere and
travel from rarer to
denser medium.

7. Advanced sunrise and delayed sunset
 They bend slightly towards normal at
each refraction and appear to come
from apparent position of sun.
 Hence, the sun appears to rise a few
minutes before the actual rise and for
the same reason, it continues to be seen
a few minutes after it has actually set

8. Twinkling of Stars
 The starlight on entering
earth’s atmosphere,
undergoes refraction
continuously before it
reaches observer.
 Since the refractive index
of earth’s atmosphere is
gradually changing, the
atmosphere bends the
starlight towards the
normal, and the apparent
position of star is slightly
higher than its actual
position.

9. Twinkling of Stars
 As the path of rays of
light coming from the
star goes on varying
slightly, the apparent
position of the star
fluctuates and the
amount of light entering
the eye flickers..!!

10. Why don’t planets twinkle?
 The planets are much closer
to the earth, and thus are
seen as extended sources.
 If we consider a planet as a
collection of large number
of point sized sources of
light, the total variation in
the amount of light entering
our eye from all the
individual point sized
sources will average out to
zero, thereby nullifying the
twinkling …effect..!!

11. Apparent flattening of sun’s disc at
sunrise and sunset
 If the sun (or moon) is low
above the horizon, the
optical path of the light
through the atmosphere is
very long, and the
atmosphere usually has a
layered structure: different
temperature gradients and
pressure.
 Refraction of the light by
these layers can cause the
sun's disk to be deformed,
flattened or distorted.
Inferior and superior
mirages are responsible for
the distortions.

12. MIRAGE:MOST NOTICEABLE
 A highway mirage is an
inferior mirage which
can be seen very
commonly on roadways by
day or by night.
 Warm air is less dense
than cool air, and the
variation between the
hot air at the surface of
the road and the denser
cool air above it creates
a gradient in the
refractive index of the
air.

13. MIRAGE:MOST NOTICEABLE
 Light from the sky at
a shallow angle to the
road is refracted by
the index gradient,
making it appear as if
the sky is reflected
by the road's surface.
 The mind interprets
this as a pool of water
on the road, since
water also reflects
the sky.