# What is Incidence: Definition and 101 Discussions

In epidemiology, incidence is a measure of the probability of occurrence of a given medical condition in a population within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.

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1. ### I EM Power transmitted from one region to another (normal incidence)

High! I have a EM plane wave hitting normally a surface dividing universe in media 1 and 2, both without losses. So we have incident, reflected and transmitted waves. It's a simple exercise in which you are given the basic data about two media and wave incident amplitude H in medium 1. I get...
2. ### Complex Reflection and Transmission Coefficient in oblique incidence

Hello, Something has made me confused after studying the Snell equations these days. Regarding the Balanis Advanced engineering electromagnetic( the pages have been attached), and based on that the reflection and transmission coefficient can be complex I need to rewrite the (5-23a) again...
3. ### Angle of incidence and total internal reflection

the angle of incidence at A is 40°, then why did the answer key say "angle of incidence at A is just less than 90°". it is obvious that 40° is quite far from 90° right?
4. ### Treating Oblique Incidence as a Fraunhofer Diffraction Problem

I'm not sure where to start on this as I've only used Fraunhofer when it involves slits, not mirrors. Would I say it was a single slit problem so that D = width of slit (but this doesn't make sense to me because the light is reflecting not transmitting? Or an infinitely narrow slit hence nothing...
5. ### Wave propagation - Oblique Incidence

Summary:: A plane wave incident upon a planar surface - determining polarization, angle of incidence etc. 𝐄̃i = 𝐲̂20𝑒−𝑗(3𝑥+4𝑧) [V. m−1 ] is incident upon the planar surface of a dielectric material, with εr = 4, occupying the halfspace z ≥ 0. a) What is the polarisation of the incident wave...
6. ### Normal incidence of a plane polarized wave through multiple mediums

Hello everybody, I have to find the amplitudes of a wave that goes through 4 different mediums in terms of ##E_0##, suffering reflection in the first three but not the last one. I calculated the corresponding reflection indexes of the three mediums (all of them real). Following calculations, I...
7. ### I Selective filter based on angle of incidence?

I am a using a mirror to reflect an image at an angle of incidence of 10 degrees. The mirror is also at an angle of incidence of approximately 30 degrees from the viewer and it creates undesired reflections when looking at the mirror. Here is a diagram illustrating the situation. I am looking...
8. ### Incidence on a conductor at an angle greater than the critical angle

I for one don't see how ##\sin \theta_t \gt 1## is possible, even when you extend into the complex numbers. Is there even a way to order the complex numbers? Does he mean to say that the magnitude is greater than 1? Anyway here's my attempt at interpreting what my instructor is trying to say...
9. ### I What is the smallest angle of incidence necessary so that TIR occurs?

So I figure the answer is 90 degrees...but I don't feel that is what they are after?
10. ### Derive Fresnel's Equations for Parallel Incidence using Maxwell's BC's

I'd first like to preface this post with the "right answer" per wikipedia (I've seen the same answer elsewhere on more reputable websites) The thing I find trouble some is the cross terms such as ##n_2 \cos \theta_i## where indices of refraction are "mixed with the other angle". I have...
11. ### Normal incidence of light on a denser medium

When light, traveling through a rarer medium, gets reflected off at an interface with a medium of higher refractive index, it suffers a phase shift of half-wavelength. Now if it was normal incidence, the phase-shifted light would retrace its path. Does that mean the wave would cancel out?
12. ### Angle of Incidence, Propagation Constant and Wavelength

Homework Statement Light of free-space wavelength λ0 = 0.87 μm is guided by a thin planar film of thickness d = 3.0 μm and refractive index n1 = 1.6, surrounded by a medium of refractive index n2 = 1.4 critical angle = 61.04° n0 = 1.00 (a) Determine (i) the angle of incidence θ and (ii) the...
13. ### Normal incidence of EM wave - p & s polarization convention?

Hi. I'm reading a paper "Transmission of light through a single rectangular hole in a real metal" and the author refers to the incident light shown below as "p-polarized" without further specification. Note that ax > ay. Is there any convention in regarding a certain polarization as...
14. ### What is the angle of incidence?

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? 0°30°45°60° Homework Equations sin θc = nr/ni ? The Attempt at a Solution I thought that by finding the critical angle then anything above that...
15. ### I Calculating the incidence angle of the Sun

Hi all, I have some difficulties understanding a formula for calculating the incidence angle for incoming solar radiation on a sloping surface. I found that: angle of incidence calculated as cos(j) = sin((pi/2)-surface slope)*sin(altitude angle) + cos((pi/2)-surface slope)*cos(altitude...
16. ### Linear Algebra - Incidence Matrix of an RLC Ckt

<Moved from a homework forum. Template removed.> I can't find any documentation on how to do this. I remember in linear algebra how to find the incidence matrix of an electrical network of purely resistors. Put how do I find it of a RLC circuit with resistors, inductors, and capacitors? I can't...
17. Q

### Plane wave angle of incidence calculation

Good afternoon! Please help me figure out the mathematics of this simple plane wave question! 1. Homework Statement 2. Homework Equations n1*sin(theta1)=n2*sin(theta2) The Attempt at a Solution I need help calculating the angle of incidence. I found the propagation vector for incidence...
18. Y

### Calculating Incidence Angle for Tilted Plate and Light Source

Homework Statement A plate is subjected to rays from a light source located 35 degrees above the horizon. The plate itself is tilted 12.5 degrees around its vertical axis reducing the exposure to the light source. Find the incidence angle between the light source and the front face of the...
19. ### Risk of Celiac Disease at 5 Yrs: 12.1% CI 9.2-15.0

Homework Statement “The risk of celiac disease at 5 years of age was 12.1% (95% CI, 9.2 to 15.0).” The question is: what do they mean with risk a,incidence rate b.cumulative incidence c.attributive risk d.population atrributive risk Homework EquationsThe Attempt at a Solution I don't...
20. ### Dielectric slab and angle of incidence

Hello! Let's consider a plane wave represented by a ray, propagating in a 2D dielectric slab. It has a medium with refractive index n_1 as its core and a medium with refractive index n_2, n_2 < n_1, as its cladding. In order for this ray to represent a mode, it must satisfy two conditions: -...
21. ### What will happen if angle of incidence on a glass slab is 0?

I have a conceptual doubt. pl help me clarify it: What will happen if angle of incidence on a glass slab is 0? will refraction take place, or reflection, or both?
22. ### I Black body, angle of incidence

I'm trying to understand the solution to an exercise. The solution claims that that the absorbed power of a black body from sunlight with an angle of incidence of ##30^\circ## is ##P=P_0\cos(30^\circ)## The reasoning here being to take the component orthogonal to the surface. However what...
23. ### Lens aligning various angle of incidence light striking it?

Assume a flat one square foot vertical plate attached 6 feet up, outside on a wall. Dozens of yards away are various solar reflectors angled to reflect sunlight onto that plate. Problem is, the plate requires to be only struck straight on at a 0 degree angle of incidence. And, all the...
24. ### Force due to radiation pressure in oblique incidence

The radiation pressure for a perfect mirror is given by: P = 2 Ef/c * cos²(θ) Where Ef is the energy flux per area (Power/A), and θ is the angle of incidence (from: https://en.wikipedia.org/wiki/Radiation_pressure) Since force due to pressure is F = PA, force due to radiation pressure become...
25. ### For which incidence angle the ray won't come out of the prism's surface....

Homework Statement A ray of light falls on the surface AC of a prism with a straight angle and with two sides equal. For which incidence angle the ray won't come out of the surface AB. The index of refraction for the prism is n=2. Homework Equations sina/sinb=n2/n1 The Attempt at a Solution...
26. ### When the incidence angle is equal to the angle of refraction

Homework Statement When the incidence angle is equal to the angle of refraction? Homework Equations sina/sinb=n2/n1The Attempt at a Solution I think as a=b => sina=sinb => n1=n2. We should have the same environment? But is that refraction?
27. ### Angle of incidence and refraction

Hello PF users hope all is well! I need a reminder of the formulas needed in order to get "Sine of angle of incidence" "Sine of angle of refraction" And "Index of refraction". The only information I have available now is "Angle of incidence" And "Angle of refraction" I'm guessing...
28. ### Finding angle of refraction given angle of incidence?

Can someone help me in solving this question ? my attemp is sin42/sin 90 to get the refractive index then n =sin i/sin r to get c and for b n=1/sinc
29. ### Field frequency and angle of incidence in optical waveguides

Hello! In this previous post, most replies point out that it is not possible to predict the angle of refraction (and so the frequency) at a certain interface, given the wavelength of the original signal. In particular, But when dealing with optical waveguides, it seems to be different. I am...
30. ### Does the angles of incidence affect speed in glass

I understand that the refractive index of different materials affects the speed of light but does light change speed in glass when entering from air at different angles of incidence?? if not what causes the variation in lateral displacement?
31. ### Angle of Refraction through a Prism

Hello everyone, I am trying to figure out how to explain an aspect of this question to my students, but cannot seem to recall the geometry that explains the textbook's approach. In the figure below, for part (b) of the question, we are using the angles of refraction at the left boundary to...
32. ### Wave reflection and refraction, relations between angles

Hello! This post is strictly related to my previous one. Let's consider the same context and the same image. Regarding the oblique incidence of a wave upon an interface between two dielectric, all the texts and all the lectures write an equation like the following: e^{-j k_1 y \sin \theta_i} +...
33. ### Electromagnetic wave incidence on interface

Consider the problem shown in the "wave_incidence_1.png" attached image. An electro-magnetic wave is traveling towards an interface between its current medium and a new medium, which has a refractive index n_2 \neq n_1. The interface is represented by the (x,y) plane. The electric field...
34. ### Normal incidence on 2 dielectric boundaries

Homework Statement I've not been able to do this question for years so I'd really appreciate some help. Light is normaly incident from a medium 1 with impedance Z1 through a layer of medium 2 of thickness L and impedance Z2 into medium 3 of impedance Z3. Obtain an expression for the total...
35. ### Diffraction orders of grazing incidence

Homework Statement We have a honeycomb lattice. There is an incident wave of 400 nm, whose wavevector has an angle of 75 degree with the surface's normal. This problem is similar to LEEDS ( low energy electron diffraction). Homework Equations What is the condition of diffraction i.e. which...
36. ### Antenna theory detection of angle of incidence

Assume a 2D problem. Given a linear antenna array, let's say 3 antennas distributed around the z axis, how could we extract the incidence angle of the received wave? Having 3 antennas equally spaced by λ/2 in the z axis and connected to each other, the result gain would be a function of ϑ (angle...
37. ### Question about solar energy: angle of incidence

My understanding is that the seasonal variation in temperature, amongst many other things, is a reflection of the Earth's tilt. Simply put, at the equator, sun rays fall "straight down" (100% vertical), and all of their energy hits the surface of the Earth. At different latitudes, these rays...
38. ### Angle of incidence and reflection

I am trying to write a java code where the user inputs the height at which a solid body approaches a sphere of radius R and outputs the angle ##\theta## at which the body bounces off the sphere. I have all my code written is just that I don't know how to derive the equation that calculates the...
39. ### Why angle of incidence equal to angle of reflection

I want to why in ray optics. Angle between incident ray and reflecting surface normal is equal to angle between reflected ray and reflecting surface normal. Simply why angle of incidence is equal to angle of reflection?
40. ### Deriving Equation Relating Angle of Incidence to the Angle of Refracti

Homework Statement Derive an equation relating the angle of incidence and the angle of refraction as light travels from air to glass. Do it in the form of Θ2/Θ1 = expression Homework Equations I think the equation to use here is Snell's law. Right? n1sinΘ1 = n2sinΘ2 n1 = nair =...
41. ### Find the Angle of Incidence for Total Internal Reflection in a Glass Sphere

Homework Statement A ray of light incident on a glass sphere (refractive index sqrt 3) suffers total internal reflection before emerging out exactly parallel to the incident ray. What was the angle of incidence? μ = refractive index of the glass sphere, i = angle of incidence, r = angle...
42. ### Defining Plane of Incidence for Normal Polarized Wave

How to define the plane of incidence for normal incidence of a plane polarized wave? Is the reflection coefficient defined by ordinary, extraordinary, or the combination of both waves? Thanks for the help!
43. ### Need help with angle of incidence of light through a prism

Homework Statement The direction of the ray of light enters equilateral 60° glass prism normal to the surface as shown in attached image refracted index of the prism material for the violet light is 1.651 (a) What is the angle of incidence on the surface A-B? (b) Does total internal...
44. ### Fresnel's Equations/ Normal Incidence/ R and T coefficients.

The question asks to use Fresnel's equations at normal incidence to find the ratio of the refractive indexes of the two materials. We are told equal energy is transmitted and reflected and that both media are non-magnetic and non-conducting dielectrics. So I know that the ratio of Er/Ei and...
45. ### MHB Angle of Incidence: Subtracting 90 Degrees Explained

I do not understand why we do we subtract from 90 degrees when finding the final answer for angle of incidence?
46. ### Does the incidence angle and refraction angle have to add up to 90

does the incidence angle and refraction angle have to add up to 90 I'm trying to figure out the geometry of thin film refraction!
47. ### Tax incidence and Price Elasticity

Hello everyone, I see that economists define a formula to calculate how the tax is shared between consumers and suppliers. They call it "Pass-thorugh" fraction: Customers share = (-PED)/(PES-PED) Suppliers share = PES/(PES-PED) However I see this doesn't work when I use it with...
48. ### Angle of Incidence on a spherical lens

Firstly, I'm sorry if this is incorrect or if there is a specific place for such questions but as this is neither a problem posed to me, nor something that has been taught - I have little background with which to work with but it is something I need to do for my ERT and 2 maths teachers have...
49. ### How does the eye detect the angle of incidence?

I don't really know too much about the human body, but this is my rough understanding of how vision works: light comes from a source, like the sun, it hits an object, and then if it's of the right frequency it's reflected by the object and then enters one of your two eyes, where it is refracted...
50. ### Refraction at grazing incidence

Homework Statement I have a problem with the question in the attachment below. I have no idea on how to proceed as I thought that the ray of light would continue to travel in a straight line with no refraction whatsoever. Homework Equations n1sinθ1=n2sin2 The Attempt at a...