APPARATUS REQUIRED
1. Glass slab
2. A sheet of white paper
3. Drawing board
4. Scale, protractor, pencil, pins
5. Compass
THEORY
Refraction: The phenomenon of bending of light when it travels from one medium to another medium is known as refraction.
Snell’s law:
According to this law the ratio of the sine of the angle of incidence (i) to sine of the angle of refraction (r) is always constant This constant ratio is called refractive index (u).
i.e.
μ₁ = Sin (1) / Sin (r)
If Pa and Pg are the length of the perpendicular in air and in glass, then refractive idea is given by
H₂ = Sin(i) / Sin(r) = Pa/hypotenuse / Pg/hypotenuse
therefore, H₂ = Pa/Pg
ORSERVATION:
Least count of scale = 0.1cm
least count of protector = 1°
Table 1: (Using protector)
| S.N. | Angle of incident (i) | Angle of refraction(r) | Sin(i) | sin(r) | H= sin(i)/sin(r) | Mean H |
| 1 | angle I1ON= 1O° | angle MOR1= 6 | 0.17 | 0.10 | 1.7 | |
| 2 | angle I2ON= 20° | angle MOR2=11 | 0.34 | 0.19 | 1.79 | |
| 3 | angle I3ON= 30° | angle MOR3= 18 | 0.5 | 0.30 | 1.66 | 1.65 |
| 4 | angle I4ON= 40° | angle MOR4= 25 | 0.64 | 0.42 | 1.52 | |
| 5 | angle I5ON= 50° | angle MOR5= 29 | 0.76 | 0.48 | 1.58 |
Table 2: (without using protector)
| SN. | Incident ray | Refracted ray | μ= Pi/Pr | Mean (μ2) |
| 1 | 0.7 | 0.4 | 1.75 | |
| 2 | 1.4 | 0.7 | 2 | |
| 3 | 2.1 | 1.1 | 1.9 | 1.82 |
| 4 | 2.7 | 1.5 | 1.8 | |
| 5 | 3.3 | 2 | 1.65 |
CALCULATION
Refractive index of the glass slab
1) Using a protector, H₁ = 1.65
2) Without using a protector, H₂ = 1.82
RESULT
The refractive index of glass slab: H1+ H₂ / 2
= 1.65+1.82 / 2
= 1.735
PERCENTAGE ERROR
Percentage error in refractive index of glass slab is
= |standard value – observed value / standard valve|x 100%
=|1.5-1.735 / 1.5| x100%
=15.67%
PRECAUTION
1. The pins should be exactly radical
2. The distance between two pins should be about 40cm. Retracted images are observed 30 cm from the glass slab.
3. Angles should be measured with?
OBSERVATION:
Least count of scale = 0.1cm
least count of protector=
Table 1: (Using a protector)
| S.N. | Angle of incidence(i) | Angle of refraction(r) | Sin(i) | Sin (r) | μ=sin(i)/sin(r) | Mean μ |
| 1 | 10° = angleI1ON | 6° = angleMOR1 | 0.1736 | 0.1045 | 1.66 | |
| 2 | 20° = angleI2ON | 12° =angleMOR2 | 0.342 | 0.225 | 1.52 | |
| 3 | 30°= angleI3ON | 19° =angleMOR3 | 0.5 | 0.355 | 1.408 | 1.4998 |
| 4 | 40°= angleI4ON | 26° = anglMOR4 | 0.6427 | 0.4383 | 1.466 | |
| 5 | 50°= angleI5ON | 32° =angleMOR5 | 0.766 | 0.5299 | 1.445 |
Table: 2 (without using protactor)
Perpendicular on
| S.N. | Incident rays (P₁) cm | Refracted ray | μ = Pi/Pr | Mean μ |
| 1 | P1N1 = 0.5 | Q₁M₁ = 0.4 | 1.25 | |
| 2 | P₂N₂ = 1.1 | Q2 M2 = 0.7 | 1.571 | |
| 3 | P3 N3 = 1.6 | Q3 M3 = 1.1 | 1.45 | 1.4364 |
| 4 | P4 N4 = 2.1 | Q4 M4 = 1.4 | 1.5 | |
| 5 | P5 N5 = 2.4 | Q5 M5 = 1.7 | 1.411 |
CALCULATIONS:
Refractive index of the glass slab
i) Using a protactor, (μ) = 1.4998
ii) Without using a protactor, (μ) = 1.4364
RESULT:
The mean refractive index of glass slab is found to be 1.4681.
PERCENTAGE ERROR:
Percentage error in refractive index of glass slab is
=|Standard valve – observed value / Standard valve| x 100%
=|1.5-1.4681/ 1.5| x 100%
= 2.12%
CONCLUSION:
Hence, the laws of refraction were verified and determined the refractive index of a glass slab.