# What is Penetration depth: Definition and 32 Discussions

Penetration depth is a measure of how deep light or any electromagnetic radiation can penetrate into a material. It is defined as the depth at which the intensity of the radiation inside the material falls to 1/e (about 37%) of its original value at (or more properly, just beneath) the surface.
When electromagnetic radiation is incident on the surface of a material, it may be (partly) reflected from that surface and there will be a field containing energy transmitted into the material. This electromagnetic field interacts with the atoms and electrons inside the material. Depending on the nature of the material, the electromagnetic field might travel very far into the material, or may die out very quickly. For a given material, penetration depth will generally be a function of wavelength.

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1. ### I Absorption cross section of light in air

When I woke up today in the morning, I had the stupid idea of trying to remember some of my knowledge from university. As it turned out, this was easier thought than done, especially given my still drowsy state of mind. I want to roughly estimate the penetration depth of visible light in air...
2. ### Finite potential well problem penetration depth

I don't understand where I went wrong, the formula and calculations which I have attached are correct...please do help if anyone can spot the mistake.
3. ### A Penetration depth of a ion beam coupled with an EM wave

A Ion source is a device that allows creating ion beams (e.g. argon ions) and to project them outside the device, for example to be further processed by a particle accelerator, or to irradiate materials or biological tissues etc. Now, suppose the ion beam is coupled with an EM wave, especially...
4. ### A EM Penetration Depth Into the Ground

Hello, I'm wondering about the best EM to penetrate deep into ground and sense/detect what's there. The authors here (https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005JE002528) are recommending P-band with 430 MHz to probe few meters into the ground of Mars; that's about 70-cm...
5. ### Thermal penetration depth experiment

I doing an experiment that involves thermal penetration of copper. Please advise me where to post if I choose the wrong spot. This experiment is being done with what I have on hand and my ability to work the materials. Materials 2.75 gal pot of water 6qt pressure cooker 100+lb of stripped...
6. ### A Mode Field Diameter and Penetration depth of the Evanescent field

Source: fobasics.blogspot.com Source: scirp.org As it is shown in the first pic above that the mode field diameter is defined as the mode field decreases to 1/e (in intensity 1/e^2), if I take the mode field and subtract the core's diameter then I divide it by 2, should I get the penetration...
7. ### Penetration depth and step potential

Homework Statement I am trying to figure out the average penetration depth into a finite step potential, similar to this thread: https://www.physicsforums.com/threads/qm-barrier-penetration.104641/ But instead of just estimating the depth as ##\frac{1}{\kappa}##, i would like to calculate it...
8. ### I Stopping Power and Range units for charged particles

Dear members, The unit of stopping power is given as Mev/cm in many sources. It is easy to comprehend this unit.The mass stopping power, which is the total energy lost per path length by a charged particle, is defined as the division of MeV/cm to the density of investigated material, g/cm3, and...
9. ### Finding Impact Depth: Most Realistic Way Possible

I'm trying to find the impact or penetration depth of a projectile in the (reasonably) most realistic way possible. I assume this has many factors including velocity, the densities of both materials, shapes of both materials, the medium of which the projectile travels through, gravity, etc...
10. ### A What Happens When Particles Travel in Non-Crystal Directions?

Can someone explain this paragraph especially the bold part in simpler language: "If it is not in a major crystal direction or plane ("random direction", Fig. 2), it is much more likely to undergo large-angle scattering and hence its final mean penetration depth is likely to be shorter." full...
11. ### A Penetration Depth of General Complex Conductivity

Hi all, I'm working through chapter 2 of Michael Tinkham's Introduction to Superconductivity. On page 40, he asserts that the skin-depth for a general complex conductivity is (In Gaussian units) $$\delta = \frac{c}{\sqrt{2\pi\omega\left(|\sigma| + \sigma_2\right)}}$$ where \sigma = \sigma_1...
12. ### Penetration of falling object into sediment (after water)

Hi All, Long time absentee from the forums hoping for some direction in my new research. I've been tasked to look into the stages of motion of objects (dropped from various heights), hitting a body of water (of various depths) and eventually hitting the seabed (of various sediment types). I am...
13. ### Penetration depth of a microwave

Hi, according to http://www1.lsbu.ac.uk/water/microwave_water.html and other sources the penetration depth of a microwave wave is proportional to the square root of the dielectric constant divided by the dielectric loss. For me it makes sense that as the dielectric loss increases more energy is...
14. ### B Hammer & a nail -- Calculating penetration depth into wood for first strike

If you know the weight of the hammer, and the velocity it hits the nail. What would you need to know about friction forces, etc in order to calculate how far it is driven down into the wood? So assume the hammer weight 0,5kg and it is being swung at 50m/s when it hits the nail. Friction is (?)...
15. ### Penetration Depth Review - Exam Prep

This is a review problem for an upcoming exam. I'm pretty sure a problem very similar to this will be on the exam. And surprise surprise I'm freaken lost. 1. Homework Statement A high index prism is used to launch an evanescence wave at the water/prism interface as shown. A He-Ne laser (λ =...
16. ### Quantum Tunneling of a conduction electron in Copper

Homework Statement A conduction electron moves through a block of Cu until it reaches the surface. At the surface the electron feels a strong force exerted by the nonuniform charge distribution in that region. This force tends to attract the electron back into the metal which is what causes the...
17. ### Calculating Penetration Depth for TIR of Evanescent Waves at Glass-Air Interface

Homework Statement : Calculate the penetration depth of an evanescent wave undergoing TIR from glass (n = 1.5) to air interface, such that the amplitute is reduced to 1/e times its original value. Wavelength of the incident light is 5000 angstroms and 60 degrees. First make sure that incident...
18. ### Why is the expression for sheet resistance given without demonstration?

Hello! I have in my notes an expression for the sheet resistance of a uniform conductor with length L, width W = L and thickness t. It is R_{\square} = \displaystyle \frac{\sqrt{\displaystyle \frac{\pi f \mu}{\sigma}}}{1 - e^{-t/\delta}} = \displaystyle \frac{1}{\sigma \delta} \frac{1}{1 -...
19. ### UV Light Penetration: Explaining Heuristic of Photopolymers

For a photopolymer, the heuristic goes that longer wavelengths of UV light penetrate deeper than shorter wavelengths of UV light. For example, the UVA spectrum penetrates more deeply into the photopolymer than the UVC spectrum. What is the best way for this to be explained?
20. ### How Do Longer UV Wavelengths Penetrate Deeper into Photopolymers?

For a photopolymer, the heuristic goes that longer wavelengths of UV light penetrate deeper than shorter wavelengths of UV light. For example, the UVA spectrum penetrates more deeply into the photopolymer than the UVC spectrum. What is the best way for this to be explained?
21. ### What Factors Affect Ultrasound Penetration Depth?

Hi, I want to calculate the penetration depth of some different frequency ultrasound transducers. I know that it depends on the attenuation of the medium but not sure where these types of figures will be hiding. I assume that once the dB lost for the depth is equal to the dB generated, this is...
22. ### What is potential barrier against the photon penetration

It is known that the penetration depth of photon into a material depends on the energy of the photon, density and atomic number of the material; because the photon energy is normally smaller than the potential against the penetration of photon, which is the potential barrier, so the incident...
23. ### Superconductor coherence length and penetration depth

Homework Statement I have a lot of information about 2 different superconductor materials; indium and lead. The indium is pretty much 100% indium with no impurities, and the lead is unknown purity. I have the temperatures and magnetic fields at which they are superconducting and the...
24. ### Penetration depth below surface - Free Fall

So here is the scenario: an adult male 80kg, 6ft tall, slim build free falls into the open ocean feet first, hands locked into the groin. Speed at entry can be 200km/hr. We can assume the water is perfectly stile in reference to the surface tension. and for the body we can estimate some factors...
25. ### Bullet hits a block, penetration depth and velocity

Homework Statement A bullet with mass and speed v hits a wooden block of mass M that is situated at rest on a frictionless surface. It penetrates the block and gets trapped inside it as a result of a constant retardation force F_{ret} that opposes relative motion between the two objects...
26. ### Dimensional analysis of the london penetration depth

hi guys. i have the london penetration depth defined as \lambda_l = \sqrt{\frac{m^{**}}{4\pi n_{s} e^{2}}}. i'm trying to figure out the dimensionality of it...surely it must be a length, but i get [(Kg)(m^{3})(A^{-1}s^{-1})]^{0.5} in SI units. am i doing something wrong? cheers.
27. ### London- vs Josephson penetration depth

Hi everyone. What is the difference between the London penetration depth and the Josephson penetration depth? Both of them have to do with the penetration of a magnetic field into the superconductor as far as I can see...
28. ### Frequency and penetration depth

why does the increase of sound frequency will decrease the penetration depth? how can this related to diffraction of sound?? Is it because they can be easily reflected?? need answer desperately, thx
29. ### Calculating Penetration Depth of Staple Shot Into PVC

penetration depth??! How would I find the penetration depth of a staple shot into a material by a staple gun. It doesn't have to be specific to a staple. Material I am concerned with is pvc. Even a general approach is fine. I know the force opposing the staple going in is the friction of the...
30. ### Find Penetration Depth of Staple Gun in PVC

Penetration depth? How would I find the penetration depth of a staple shot into a material by a staple gun. It doesn't have to be specific to a staple. Material I am concerned with is pvc. Even a general approach is fine. I know the force opposing the staple going in is the friction of...
31. ### Momentum and penetration depth

Many textbooks derive the relativistic momentum from the penetration depth of a bullet in a resistive media, considering that momentum is proportional with the penetration depth. Do you know a transparent and correct way to the problem?
32. ### Finding Penetration Depth in a finite well

The problem is as follows: A 50-eV electron is trapped between negligible-width capacitors charged to 200V (each with an exit hole). How far does its wave function extend beyond the capacitors? I know the answer is 1.6 x 10^-11 m, but I cannot get to that. Any ideas? -Jason