What is meant by refraction of light? State Snell’s law of refraction - Leaving Cert Physics - Question 9 - 2008

Snell's law states that the ratio of the sine of the angle of incidence ( (i)) to the sine of the angle of refraction ( (r)) is a constant, which can be expressed mathematically as:

$n = \frac{\sin(i)}{\sin(r)}$

where n represents the refractive index of the two media.

Using the lens formula, we can relate the object distance (u), image distance (v), and focal length (f) of the lens:

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$

Given that the maximum power of the eye is 64 m-1, we find:

$f = \frac{1}{P} = \frac{1}{64} = 0.0156 \text{ m}$

For the nearest object distance, we set:

$v = -7.14 ext{ cm} = -0.0714 ext{ m}$

Substituting into the lens formula:

$\frac{1}{0.0156} = \frac{1}{u} - \frac{1}{0.0714}\Rightarrow u \approx 0.09 \text{ m} = 9 ext{ cm}$

Thus, the nearest object can be placed approximately 9 cm in front of the eye.

Using the total power formula for the eye:

$P_{max} = P_{1} + P_{2}$

where we know:

$P_{1} = 38 \text{ m}^{-1}$

and from the given total power:

$P_{max} = 64 \text{ m}^{-1}\Rightarrow P_{2} = 64 - 38 = 26 \text{ m}^{-1}$.

So, the maximum power of the internal lens is 26 m-1.

To find the refractive index (n) of the cornea, we can use Snell's law at air-cornea interface:

n = \frac{\sin(37^{\circ})}{\sin(27^{\circ})

Calculating:

$n = \frac{\sin(37^{\circ})}{\sin(27^{\circ})} = 1.3256$

Thus, the refractive index of the cornea is approximately 1.33.

A diagram representing the interface of water and cornea can be drawn with a ray of light refracting as it enters from water into cornea. Draw a straight line to represent the light ray, indicating the angles of incidence and refraction at the boundary, as well as the normal line to the boundary.

Underwater, the cornea does not act efficiently as a lens because its refractive index becomes similar to that of water. This results in a negligible difference in refractive power, making it ineffective in bending light to focus on the retina.

The maximum power of the eye is given as 64 m-1. This includes the contributions from both the cornea and the internal lens.

Objects appear blurred when viewed underwater because the internal lens of the eye is not powerful enough to focus the light from the external environment onto the retina; hence, the images are out of focus.

Wearing goggles creates a medium (air) between the eye and the water. This allows the light to refract properly as it passes through and into the cornea, enabling the eye to focus images correctly onto the retina and see clearly.