Page 177 - Physics_Form_2

Refraction and dispersion of light

surface tension. Wait for some time In this activity, the refractive index
until the water is still. of water has been determined using a
7. Repeat steps 3 and 4. concave mirror method. As the known
refractive index of water is 1.33, this
8. Measure and record the new height, method gives a good estimate of the
′ h of the optical pin from the pole
FOR ONLINE READING ONLY
(P) of the mirror. refractive index of water. Therefore, the
9. Repeat the experiment using other method can be useful in determining the
refractive indices of different liquids.
concave mirrors of different focal
lengths.
10. Record your results in a table similar Task 5.1
to Table 5.2 and calculate the average
refractive index of water. Use the apparent depth method to
determine the refractive index of
Table 5.2 water. How accurate is your value of
Focal Height Height Refractive refractive index?
length h (cm) ′ h cm index
f (cm) ′ h
η = Example 5.1
h
Find the index of refraction for a certain
medium, assuming light in air enters
the medium at an incident angle of
30º and the angle of refraction is 22º.

Solution
Note: Use spreadsheet software to: Given, the incident angle ( ) 30i = o ,
Input your data from Table 5.2. angle of refraction ( ) 22r = o , η = ?

(a) Calculate the refractive index using sin(i)
h η g =
the formula η = . a sin(r)
′ h
(b) Create a graph to visualise the sin30

relationship between focal lengths sin 22  1.33
and the calculated refractive indices.
Therefore, the refractive index of the
Questions medium is 1.33.

(a) Which mirror gives the most accurate
value of the refractive index of
water? Total internal reflection of light
(b) What are the possible sources of It has been established that when light
uncertainties in determining the travels from a lighter medium to a denser
refractive index of water using the one, (η < η ) the refracted light ray bends

2
1
concave mirror method? towards the normal. Conversely, when
171

Physics Form 2 Final.indd 171 25/10/2025 10:27