Incidence Definition and 101 Threads

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. Y

    Question on phasors at boundary of oblique incidence.

    A plane wave travels in ##\hat k_I=\hat x \sin\theta_I+\hat z \cos \theta_I## direction hitting a boundary formed by xy plane ( z=0). The incidence wave is in the plane of incident formed by xz plane where y=0. We let ##\tilde E_I(\vec k_I)= \hat x E_{I_x}+\hat y E_{I_y}+\hat z E_{I_z}...
  2. Y

    Question in reflection and transmission at oblique incidence.

    I am reading Griffiths p387. It is my understanding that \tilde E(\vec r,t)=\hat r E_0 e^{j(\omega t-kr)} Where ##\vec r =\hat x x+\hat y y+ \hat z z## is the positional vector from the origin to the observation point ( x,y,z). \Rightarrow\;\tilde E(\vec r,t)=\hat r E_0...
  3. S

    Finding the incidence angle for refraction

    Homework Statement I am to find the angle of incidence of a light ray before it undergoes refraction. Light is refracted in the second medium at an angle of 76 degrees measured from the normal. The second index of refraction is 1.386. The index of refraction for the initial or first medium...
  4. A

    Why incidence and adjacency matrices (graph theory)h

    My book introduces the concept of adjacency and incidence matrices but I don't understand its use. Normally we shift from mathematical symbols and representation to graphical interpretation like in Cartesian graphs - to visualize functions better we draw them on a graph. But here we are doing...
  5. S

    If a beam of light with an angle of incidence

    Homework Statement The maximum depth of Lake Baikal, in Russia, is 1780.7 m, making it the world’s deepest freshwater lake. If a beam of light with an angle of incidence of 59.42o enters the water from the air, what is the horizontal distance between the point where the light enters the...
  6. L

    Proving Every Line is Contained by Two Planes: Using Incidence Axioms

    I need to prove that every line is contained by at least two planes using only the incidence axioms. This is what I have so far... Conclusions Justifications 1. Let l be any line. Given 2. l has at least two...
  7. E

    Waves Unit- Angle of Incidence

    Homework Statement http://imgur.com/LDx7IHomework Equations http://en.wikipedia.org/wiki/Snell%27s_law The Attempt at a Solution I'm not really sure on the approach to take for this question. Since it proves 2 angles, Snell's Law could prove to be beneficial. Thanks for the help!
  8. G

    Detecting changes in incidence rate

    Hi! I have rare events over time (about 200 incidences) and I'd like to detect when the time rate of these increase, i.e. at which point more events per time start to occur. Do you know a solid statistical tool to analyze that? I'd also like to know if the change is real evidence or just random.
  9. B

    Fresnel equations at normal incidence

    Hello everybody, I have a question about the Fresnel equations at normal incidence. My textbook gives the reflection coefficients as: (1) perpendicular polarization rs=( n1*cos(theta1)-n2*cos(theta2) ) / ( n1*cos(theta1)+n2*cos(theta2) ) (2) parallel polarization rp=(...
  10. R

    Find angle of incidence given deviation angle

    Homework Statement A ray of light passes from air into benzene. For its deviation angle δ = |θ1 - θ2| to be 9.5°, what must be its angle of incidence? The refractive index of benzene is 1.501. Homework Equations Snell's law The Attempt at a Solution From Snell's law we have sin...
  11. F

    Optics - Transmission of plane wave at oblique incidence

    I have 2 questions that need help with, Considering the following plane wave, E= 30 (0.866 i + 0.5k)exp{i(-0.5x + 0.866z)} firstly how can i deduce the direction of the electric field oscillations? And finally, if the wave is incident on a dielectric interface between medium of Er=2...
  12. G

    Transmission and reflection for olique incidence at a uniform dielectric slab

    1. Homework Statement A di-electric slab of thickness d is between two differing dielectric media (u0,e0/u1,e1/u2,e2). What is the total reflection at the first interface and transmission through the second interface of the slab. The incident wave is in the x-z plane with an angle of...
  13. P

    Equations of Motion for 'Perturbed' Or 'Oblique Incidence' Orbits?

    Hi, I've been doing a Q where particles undergo circular/near-circular motion in an electric field. The electric field varies as 1/r. With the first particle, they set it off tangentially to the field lines, so it undergoes circular motion. With the second particle, they set it off at a...
  14. D

    Angle of deviation and angle of incidence?

    Homework Statement This is a two part problem: 11) The index of refraction for violet light in silica flint glass is 1.66, and that for red light is 1.62. What is the angle of deviation for the red ray passing through a prism of apex angle 59.6◦ if the angle of incidence is 54.8◦...
  15. G

    Refraction at normal incidence

    high All, Just got to thinking, if we have a beam of light normal to a flat surface, and the surface is that of an object which has a variable refractive index across the transverse beam direction, will some of the light be bent away from the normal on the other side of the object? i.e. if...
  16. A

    Why do we measure the angle of incidence or reflection

    Why do we measure the angle of incidence or reflection (or say refraction even) w.r.t normal to the surface and why not w.r.t the horizontal surface?
  17. M

    Show Poincare Disk is incidence geometry

    Homework Statement I have to show that the Poincare disk satisfies the incidence axiom that any line contains at least two points. Homework Equations There are two kinds of lines on the Poincare disk. I've found 2 points for the first kind, which are straight lines going through the...
  18. N

    Measuring the angle of incidence into a fiber

    Hello everyone, I'm currently working on a little project that has been puzzling me for some time. If you send a laser beam into a fiber, the ingoing angle is sometimes slightly different than the outgoing angle. To measure this ratio of angles, I am currently using a setup that looks like...
  19. J

    Incidence matrix vs Adjacent Matrix

    What is the difference between an http://en.wikipedia.org/wiki/Incidence_matrix" . They sound the same to me but this paper says they are different: http://eprints.pascal-network.org/archive/00005332/01/barber_Newton.pdf edit: My guess is that adjacent matrices refer to non directed graphs so...
  20. S

    Angle of incidence, angle of refraction and angle of reflection

    Homework Statement A light ray strikes the surface between two transparent materials as shown. Each angle is labeled with a letter. Give the letters for the angle of incidence, angle of refraction and angle of reflection, in that order Homework Equations...
  21. S

    Angle of Incidence with partial reflection and partial refraction

    Homework Statement A beam of light in air strikes a piece of glass (n=1.51) and is partially reflected and partially refracted. Find the angle of incidence if the angle of reflection is twice the angle of refraction. Homework Equations n1sintheta1 = n2sintheta2 The Attempt at a...
  22. B

    Size of the angle of incidence?

    If the angle between an incident ray and a reflecting surface is 23°, what is the size of the angle of incidence? Im not quite sure what the formula for this would be, I can't find it in my book :| any help would be very much appreciated. Thank you
  23. B

    Oblique incidence for Electromagnetic Waves

    I'm a bit confused, when drawing the diagram for oblique incidence, how do I choose which way to draw the electric field? For example, I know the direction of the wave is in the plane of incidence and the wave vectors are simply arrows in the direction of the wave that I draw - and that the E...
  24. A

    Grazing incidence on an acoustic tile, how to determine grazing angle?

    Homework Statement Acoustic tile which is locally reacting, for a frequency of 400 Hz, it has a normal-incidence specific impedance of 1500+i3700 (Kg/m2s). A plane wave in Air of 400 Hz sound with a pressure level of 86 dB in the absence of reflection is incident on the tile at an Angle X. How...
  25. M

    Why Does the Calculator Show an Error When Solving for the Angle of Incidence?

    b]1. A light beam coming from an underwater spotlight exits the water at an angle of 68° to the vertical. At what angle of incidence did it hit the air-water interface from below the surface? [b]2. snell's law n1sin\Theta1=n2sin\Theta2 [b]3. sin\Theta1=1.33(sin68) After doing this...
  26. R

    Snell's law, critical angle, and angle of incidence

    Homework Statement A pair of students measure the refraction of light in passing from acetone into air for several angles. When the angle of incidence is 30, the angle of refraction is 42. b) What is the angle of incidence (in degrees) when the refracted angle is the critical angle? Homework...
  27. F

    How To Propogate Uncertainties (Angle of Incidence and Angle of Reflection)

    Hello fellow physicists :) I have recently done an experiment and am trying to propagate the uncertainty. Unfortuantely, I haven't done that in years, and need to remember how its done. For example: When theta= 20 (+-2) I want to find sin20 and the uncertainty: sin20=0.34 (+-?) How can I...
  28. J

    Transmitted Field (with greater than critical-angle Incidence)

    Definition: The phase velocities of the incident, reflected, and transmitted fields must be equal on the boundary. Another way to represent this relationship for the incident and transmitted fields is: \beta_{1}sin(\theta_{i}) = \beta_{2}sin(\theta_{t} \Rightarrow sin(\theta_{t}) =...
  29. B

    Can the angle of refraction be equal to the angle of incidence?

    Snell's law says n1sin(theta1) = n2sin(theta2) The angle of refraction theta2 can be greater or less than the angle of incidence theta1. That's fairly obvious. My question is if theta2 = theta1 then we don't have an interface (because n1 = n2) so the light is still in the same medium, and...
  30. B

    Angle of Incidence and Reflection.

    Hi, Can someone please eloborate me why the Angle of Reflection is always same as the Angle of Incidence. I want the explanation at photon and molecular interaction level. Thanks in advance. - Pavan.
  31. A

    Angle of incidence, reflection, and refraction

    Homework Statement What are the difference among angle of incidence, reflection, and refraction when light strikes two parallel surfaces? What does it mean "light is incident on film"?-is that the angle of incidence? The Attempt at a Solution I know how to find all of...
  32. K

    Transimission Of EM waves in conductors at an angle of incidence

    We know that in electrodynamic when an incident Electromagnetic wave strikes a charged barrier it can either be reflected or transmits. And both of the incident, reflected and transmitted waves are in the same plane called plane of incidence. Now, i met a problem in which they state that the...
  33. F

    Optical Path Length Difference & Constructive Interference: Normal Incidence

    Homework Statement Light falls at normal incidence onto a transparent film on a substrate as shown i. what is the optical path length difference in the case of normal incidence? ii. if nf>no and nf>ns, what is the condition for constructive interference in the case of normal incidence...
  34. A

    Is the Amplitude Coefficient of Reflection Always 0 at 90 Degrees?

    At what angle of incidence is amplitude coefficient of reflection parallel to the incidence plane 0? my solution is that by Fresnell's equation, r//=tan(i-i`)/tan(i+i`)=0, i=i`,i=90.so for whatever surface,angle of incidence should be 90. is it correct? different from the answer!
  35. S

    Maximum Angle of Incidence for Glass-Water Boundary?

    Homework Statement A 1.0-cm-thick layer of water stands on a horizontal slab of glass. Light from a source within the glass is incident on the glass-water boundary. What is the maximum angle of incidence for which the light ray can emerge into the air above the water? Homework Equations...
  36. Q

    What Angle of Incidence Causes Total Reflection of X-rays in Calcite?

    Problem: The index of refraction for x-rays of wavelength 0.708A incident on calcite is 1-1.85E-6. What angle of incidence will give total reflection of such X rays? Using Bagg's Law: n(lambda)=2asin(theta), I get and angle of -45.07 degrees. Is this all that is required of the...
  37. M

    Incidence geometry in planes and space

    Consider the system [S, L, P], where S contains exactly four points A, B, C, and D, the lines are the sets with exactly two points, and the planes are sets with exactly three points. This "space" is illustrates by the following figure: Here it should be remembered that A, B, C, and D are...
  38. M

    Angle of Incidence - Find Reflection & Refraction Angles

    a beam of light in air strikes a piece of glass (n=1.56) and is partially reflected and partially refracted. find the angle of incidence if the angle of reflection is twice the angle of refraction.
  39. C

    Angle of Incidence for Internal Reflection

    Homework Statement In the figure shown below, a light ray enters a glass slab (with index of refraction nglass = 1.65 ) at point A and then undergoes total internal reflection at point B. The medium that surrounds the glass slab is a liquid whose index of refraction, nliquid =...
  40. A

    Incidence, Refraction, Critical Angle

    Homework Statement Travellers in hot places often think that they see water in the distance, when there is nothing but land there. This effect is called a mirage. The air near the ground is very hot, and light reflects off the top of this layer of hot air. The diagram below shows how you could...
  41. B

    Max Angle of Incidence for Light Ray in Water-Glass System

    [SOLVED] Max angle of incidence...help! Homework Statement A 1-cm-thick layer of water stands on a horizontal slab of glass. Light from a source within the glass is incident on the glass-water boundary. What is the maximum angle of incidence for which the light ray can emerge into the air...
  42. A

    Draw Incidence Angle of reflection

    Homework Statement Look at the diagram. Draw the wavefronts as they would appear after the reflection. Draw and identify the following things on the diagram. Incident ray Normal Reflected ray Angle of Incidence Angle of reflection Homework Equations n/a The Attempt at a...
  43. C

    Solving the Fresnel Equations with Polarization Parallel to Plane of Incidence

    Homework Statement The question involves the fresnel equations which I have derived. However, I seem to be missing something in the simplification. I arrive at these: http://physics.tamuk.edu/~suson/html/4323/gifs/prop034.gif http://physics.tamuk.edu/~suson/html/4323/gifs/prop035.gif...
  44. W

    Blue-shift due to oblique angle of the incidence

    I posted this question in another category but no replies, probably this place is more appropriate. I read a paper and it states that "the reflection spectrum is blue-shifted due to oblique angles of incidence" without a reference. Can anyone show me the reference of this phenomenon...
  45. N

    What Is the Smallest Angle of Incidence for Light to Enter and Exit a Prism?

    Hey, I have a problem.,. I am trying to figure out smallest angle of incidence θ for which a ray can enter the left face of the prism (seen in the pic below) and exit the right face. The infomation I have: The isosceles prism has apex angle φ = 56.1° and index of refraction n = 1.42...
  46. PhysicsIsFun

    Conformal Mapping of Aerofoil at incidence

    Does anyone know what the conformal mapping of an aerofoil at incidence is? Does it use the Joukowski transformation? Or something else.. Thanks
  47. R

    Incidence angle in a Fraunhofer single slit problem

    I have to find the first minima for a single slit diffraction problem. I know the wave length and the slit size, there is an unknow angle between the incidence wave and the perpendicular line to the slit plane. I konw that i have to use the Fraunhofer euqtion for a single slit, i already have...
  48. C

    Basic angles of refraction and incidence help needed

    Basic angles of refraction and incidence help needed (help still needed) I feel silly for even asking this, but here goes. http://img501.imageshack.us/img501/905/refractionpuzzlerg2.gif The triangle represents a glass prism. The refractive index between air and the prism is 1.55. The...
  49. N

    Angle of incidence and reflection of a parabola?

    I've been playing around with parabolic mirror calculations in my free time, and right now I'm trying to derive the equation for the line that models the angle of reflection off of a point. I understand how to find the angle of incidence and that the reflection will have the same angle off the...
  50. L

    Determine the angle of incidence

    The index of refraction of ice is 1.79. Light is reflected from a smooth ice surface, and the reflected ray is completely polarized. Determine the angle of incidence. Answer in units of degrees. Can anyone help me with a formula to set this one up? I'm confused on where to start.
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