Skip to main content
Ch 34: Ray Optics
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook
Chapter 34, Problem 14

An underwater diver sees the sun 50° above horizontal. How high is the sun above the horizon to a fisherman in a boat above the diver?

Verified step by step guidance
1
Step 1: Understand the concept of refraction. When light passes from one medium to another (e.g., water to air), its speed changes, causing the light to bend. This bending is described by Snell's Law: n₁ sin θ₁ = n₂ sin θ₂, where n₁ and n₂ are the refractive indices of the two media, and θ₁ and θ₂ are the angles of incidence and refraction, respectively.
Step 2: Identify the refractive indices for water and air. The refractive index of water is approximately n₁ = 1.33, and the refractive index of air is approximately n₂ = 1.00. These values will be used in Snell's Law.
Step 3: Recognize that the angle given (50°) is the angle of refraction, θ₂, as seen by the diver underwater. You need to calculate the angle of incidence, θ₁, which is the angle of the sun above the horizon as seen by the fisherman in the boat.
Step 4: Rearrange Snell's Law to solve for θ₁: θ₁ = arcsin((n₂ / n₁) * sin θ₂). Substitute the known values: n₁ = 1.33, n₂ = 1.00, and θ₂ = 50°.
Step 5: Perform the calculation using the formula derived in Step 4. This will give you the angle of incidence, θ₁, which represents the sun's height above the horizon as seen by the fisherman.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Angle of Elevation

The angle of elevation is the angle formed by the horizontal line and the line of sight to an object above that line. In this scenario, the diver sees the sun at an angle of 50° above the horizontal, which indicates how high the sun appears from the diver's perspective underwater.
Recommended video:
Guided course
01:04
Critical Angle

Refraction of Light

Refraction is the bending of light as it passes from one medium to another, such as from water to air. This phenomenon affects how objects appear to observers in different mediums, meaning the angle at which the fisherman sees the sun may differ from the angle perceived by the diver due to the change in medium.
Recommended video:
Guided course
03:46
Index of Refraction

Geometry of Sight Lines

The geometry of sight lines involves understanding how angles and distances relate to the positions of observers and objects. In this case, both the diver and the fisherman are at different depths, and the geometry helps determine the actual height of the sun above the horizon as seen by the fisherman based on the diver's angle of elevation.
Recommended video:
Guided course
08:20
Electric Field Lines