# What is the angle of incidence?

• SmugBug
In summary: I counted reflection as refraction, because that is what the equation says. Refraction occurs when the angle of incidence exceeds the critical angle. The angle of incidence is the angle at which the light ray hits the surface. If the angle of incidence is greater than the critical angle, then the light will refract and enter into the water with a different angle. 30° is not close enough to 33.3 in my view.Please correct me if there are some mistake in this sentence. :rolleyes::rolleyes:Reflection and refraction aren't excluding phenomena, but in the trivial case theta=0 and beyond the critical (or limit) angle refraction do not appears.
SmugBug

## Homework Statement

A light ray shines from a diamond (n = 2.42) into water (n = 1.33), and no refraction occurs. What is the angle of incidence?
1. 30°
2. 45°
3. 60°

sin θc = nr/ni ?

## The Attempt at a Solution

I thought that by finding the critical angle then anything above that would be the angle of incidence where total internal reflection occurs therefore no refraction? But that would leave two right answers which cannot be the case. Is it actually just zero, and I am thinking about it wrong?

θi = sin-1 (1.33 sin 90°)/ 2.42 = 33.3 degrees

I searched for definitions of refraction. Many say it is a change in direction of the light caused by the change in medium. That would make reflection an example of refraction. Others word it as the bending of the light ray. Yet others say both, as though those descriptions are equivalent.
I would go with the first since that makes the question answerable.

I think it's a critical angle problem (limit angle) like you've done. I think your calculations are ok. , then solution is number 2.

alejandromeira said:
I think it's a critical angle problem (limit angle) like you've done. I think your calculations are ok. , then solution is number 2.
Perhaps, but there are several reasons to think otherwise.
If you count reflection as a type of refraction, and it seems to me that at least some authorities do, then the only correct answer is 1 (0°). 30 is not close enough to 33.3 in my view.
If you do not count reflection as refraction then 30° is the only incorrect answer!

haruspex said:
Perhaps, but there are several reasons to think otherwise.
If you count reflection as a type of refraction, and it seems to me that at least some authorities do, then the only correct answer is 1 (0°). 30 is not close enough to 33.3 in my view.
If you do not count reflection as refraction then 30° is the only incorrect answer!
Yes of course!
I forgot the trivial solution theta=0 . Also my English is not native and then I did not understand your previous message well.

Reflection and refraction aren't excluding phenomena, but in the trivial case theta=0 and beyond the critical (or limit) angle refraction do not appears.
Please correct me if there are some mistake in this sentence.

haruspex said:
If you count reflection as a type of refraction, and it seems to me that at least some authorities do, then the only correct answer is 1 (0°).
I don't get it. The question states that "no refraction occurs". In this case, as given by the Fresnel equation, the reflection coefficient is ##R=\left | \frac{n_2-n_1}{n_2+n_1} \right |^2=8.5\%##. This means that 91.5% is transmitted. Doesn't the transmitted light count as "refracted"? It seems to me that no refraction would occur if the angle of incidence exceeded the critical angle of 33.3o. I don't think this is a well-crafted question.

SmugBug said:

## Homework Statement

A light ray shines from a diamond (n = 2.42) into water (n = 1.33), and no refraction occurs. What is the angle of incidence?
1. 30°
2. 45°
3. 60°
Is it refraction or refracted light ?
Wiki says that Refraction is the change in direction of wave propagation due to a change in its transmission medium.
At zero angle of incidence the light beam does not change direction, you can take that no refraction occurs.
Refraction means bending of the light ray in the new medium, because of the different speed of propagation. Above the critical angle, the light does not enter into the medium with lower refractive index, so there is no refracted light,

The problems and questions of physics exams should be written with the same accuracy with which the laws of physics are written.

## 1. What is the angle of incidence?

The angle of incidence is the angle at which a ray of light or other electromagnetic radiation strikes a surface. It is measured between the incident ray and the normal, or perpendicular, line to the surface.

## 2. Why is the angle of incidence important?

The angle of incidence is important because it determines how much light or radiation is reflected, absorbed, or transmitted by a surface. It is crucial in optics, photography, and other fields where understanding the behavior of light is necessary.

## 3. How is the angle of incidence calculated?

The angle of incidence can be calculated using the equation: θi = sin^-1(n2/n1), where θi is the angle of incidence, n1 is the refractive index of the first medium, and n2 is the refractive index of the second medium. This equation is based on Snell's Law.

## 4. What is the relationship between the angle of incidence and the angle of reflection?

The angle of incidence is equal to the angle of reflection. This is known as the law of reflection and is one of the fundamental principles of optics. It means that the incident ray, the reflected ray, and the normal all lie on the same plane.

## 5. How does the angle of incidence affect the brightness of reflected light?

The angle of incidence affects the brightness of reflected light by determining the amount of light that is reflected. At certain angles, known as Brewster's angle, the reflected light is completely polarized and appears darker. At other angles, the reflected light is brighter due to constructive interference between the incident and reflected waves.

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