# EMP vs. Digital Camera? **URL:** \ **Category:** Factual Questions\ **Created:** [May 2, 2008, 2:43am UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701 "2008-05-02T02:43:41Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [May 2, 2008, 2:43am UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/1 "2008-05-02T02:43:41Z")
Okay, I’ll just spit it out: what would the electromagnetic pulse from a tactical nuke\* do to a modern digital video camera? Specifically, what would it do to the tape (or SD card) it was using? Would it make a difference if the camera was turned on or off at the time? Finally, what would you need need to shield said camera from an EMP? Would anything less than a Faraday cage do the job? …so, yeah, at the risk of spoilers, you can probably guess what movie inspred the question. In fact, I probably should have just put the movie name in the thread title. Would have gotten more replies that way. Ah, well. \*I can probably dredge up information on weapon yield and distance from blast for the scenario, if neccesary. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 2, 2008, 2:55am UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/2 "2008-05-02T02:55:33Z")
Even if it was off, any fine circuitry inside the camera or the memory card would almost certainly be fried due to the current pulse caused by the high induced voltages. It would be very difficult (and expensive) to adequately shield a camera against EMP. Simply surrounding it with a conductive material isn’t sufficient, since the strong magnetic component of the EMP, which is what actually does the damage, passes right through most such materials. What you need is a material which has a high magnetic permeability to essentially “conduct” the magnetic field around the interior space. This won’t entirely block out the magnetic component, but most of the flux will tend to travel through the high-permeability material and much less through the low-permeability free space inside. Once excellent such material is called mu metal, a nickel-iron alloy often used for magnetic shielding applications. But, it’s expensive and you’d need a lot of it; thickness is an important factor in magnetic shielding efficiency. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 2, 2008, 4:06am UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/3 "2008-05-02T04:06:18Z")
[QUOTE=Q.E.D.] Even if it was off, any fine circuitry inside the camera or the memory card would almost certainly be fried due to the current pulse caused by the high induced voltages. It would be very difficult (and expensive) to adequately shield a camera against EMP. Simply surrounding it with a conductive material isn’t sufficient, since the strong magnetic component of the EMP, which is what actually does the damage, passes right through most such materials. What you need is a material which has a high magnetic permeability to essentially “conduct” the magnetic field around the interior space. This won’t entirely block out the magnetic component, but most of the flux will tend to travel through the high-permeability material and much less through the low-permeability free space inside. Once excellent such material is called mu metal, a nickel-iron alloy often used for magnetic shielding applications. But, it’s expensive and you’d need a lot of it; thickness is an important factor in magnetic shielding efficiency. [/QUOTE] Magnetic component? My understanding of EMP is that it is caused by free electrons generated by x-rays from a nuclear explosion outside of the atmosphere. Where does the magnetic component come from? ---
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [May 2, 2008, 4:17am UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/4 "2008-05-02T04:17:06Z")
Outstanding reply—you’ve restored some of my faith in humanity (not much, but some. 😉 )! A brief follow-up, if I may—I’m guessing that a actual video _tape_ wouldn’t take any better to the conditions that’d fry the camera, right? And wikipedia says that the EMP from a ground level (or even low altitude) nuclear blast wouldn’t be that noticable [outside the blast radius itself](http://en.wikipedia.org/wiki/Electromagnetic_pulse)—is that about right? ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [May 2, 2008, 4:20am UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/5 "2008-05-02T04:20:55Z")
This was interesting from the[Wiki on EMP](http://en.wikipedia.org/wiki/Electromagnetic_pulse) > [@](#): > > Thermonuclear weapons are also less efficient at producing EMP because the first stage can pre-ionise the air [3], which becomes conductive and hence rapidly shorts out the electron Compton currents generated by the final, larger yield thermonuclear stage. Hence, small pure fission weapons with thin cases are far more efficient at causing EMP than most megaton bombs ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 2, 2008, 1:50pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/6 "2008-05-02T13:50:05Z")
[QUOTE=beowulff] Magnetic component? My understanding of EMP is that it is caused by free electrons generated by x-rays from a nuclear explosion outside of the atmosphere. Where does the magnetic component come from? [/QUOTE] Not quite. The EMP is a magnetic pulse generated by an intense electric current which, in turn, is caused by ionization of the surrounding air which is itself caused by x-rays emitted by Compton scattering triggered by the gamma emission of the explosion. See [Wiki](http://en.wikipedia.org/wiki/Electromagnetic_pulse) for more detailed information. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 2, 2008, 2:00pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/7 "2008-05-02T14:00:09Z")
[QUOTE=Q.E.D.] Not quite. The EMP is a magnetic pulse generated by an intense electric current which, in turn, is caused by ionization of the surrounding air which is itself caused by x-rays emitted by Compton scattering triggered by the gamma emission of the explosion. See [Wiki](http://en.wikipedia.org/wiki/Electromagnetic_pulse) for more detailed information. [/QUOTE] So, where’s your Magnetic component? ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [May 2, 2008, 2:12pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/8 "2008-05-02T14:12:17Z")
[QUOTE=beowulff] So, where’s your Magnetic component? [/QUOTE] :dubious: :rolleyes: Where you have intense electric currents, you’ll get magnetic components, right? That’s the basis of electromagnetism - changing an electrical force creates a magnetic force, changing a magnetic force creates a magnetic one. At the lowest level the waves will continue to chain to each other again and again, and that makes up electromagnetic radiation. ---
**Author:** ![mwbrooks](https://avatars.discourse-cdn.com/v4/letter/m/ba9def/32.png) [@mwbrooks](https://boards.straightdope.com/u/mwbrooks)\ **Post date:** [May 2, 2008, 2:24pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/9 "2008-05-02T14:24:25Z")
[QUOTE=beowulff] So, where’s your Magnetic component? [/QUOTE] It’s between the E and the P. 😃 (Pardon the flippancy, but chrisk already did the serious answer.) ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 2, 2008, 2:26pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/10 "2008-05-02T14:26:00Z")
[QUOTE=chrisk] :dubious: :rolleyes: Where you have intense electric currents, you’ll get magnetic components, right? That’s the basis of electromagnetism - changing an electrical force creates a magnetic force, changing a magnetic force creates a magnetic one. At the lowest level the waves will continue to chain to each other again and again, and that makes up electromagnetic radiation. [/QUOTE] I don’t think EMP is as simple as you folks would have us believe. From [here](http://www.fas.org/nuke/intro/nuke/emp.htm), it looks like the Magnetic component is only significant with the blast-damage zone, so for most people it won’t be an issue. From [here](http://yarchive.net/mil/nuke_emp.html) it seems that x-rays are, the major contributor to EMP effects, like I suspected. ---
**Author:** ![postcards](https://avatars.discourse-cdn.com/v4/letter/p/8e8cbc/32.png) [@postcards](https://boards.straightdope.com/u/postcards)\ **Post date:** [May 2, 2008, 3:10pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/11 "2008-05-02T15:10:21Z")
[QUOTE=Ranchoth] …so, yeah, at the risk of spoilers, you can probably guess what movie inspred the question. In fact, I probably should have just put the movie name in the thread title. Would have gotten more replies that way. Ah, well. [/QUOTE] I can’t guess. Care to elaborate? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 2, 2008, 4:19pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/12 "2008-05-02T16:19:47Z")
[QUOTE=beowulff] From [here](http://yarchive.net/mil/nuke_emp.html) it seems that x-rays are, the major contributor to EMP effects, like I suspected. [/QUOTE] That doesn’t say what you think it does. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 2, 2008, 5:01pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/13 "2008-05-02T17:01:13Z")
[QUOTE=Q.E.D.] That doesn’t say what you think it does. [/QUOTE] Am I misunderstanding this? > [@](#): > > During detonation (within the first few hundred nanoseconds), the prompt _gamma_ > radiation generated by the primary event is absorbed and thermalized in the > compressed and ionized material that made up the outer layers of the bomb. The > range of prompt _gamma_ radiation is no more than 100m from ground zero > (considerably less in practice). The radiation from the bomb is a more-or-less > black body spectrum whose temperature is a key part of the bomb design. The > spectral peak is in the soft X-ray region and it’s those thermal X-rays that > ionize the atmosphere to generate the source region. Glasstone and others refer > to _gammas_ causing the source region disassociation but the size of the source > region is large enough (hundreds of miles at high altitude) that gammas _can’t_ > play a significant part. **It’s the long range of X-rays in rarified air that > makes the EMP from a high altitude (but not exoatmospheric) event a wide area > threat.** bolding mine. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 2, 2008, 6:48pm UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/14 "2008-05-02T18:48:09Z")
I think you might be. Yes, the x-rays initiate the EMP event. They do this by, as your source notes, by ionizing the air. This ionized air allows huge but brief currents to flow. The rest is all Faraday. ---
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [May 3, 2008, 4:15am UTC](https://boards.straightdope.com/t/emp-vs-digital-camera/447701/15 "2008-05-03T04:15:09Z")
[QUOTE=postcards] I can’t guess. Care to elaborate? [/QUOTE] Heck, sure. It’s…Cloverfield. There’s some debate online whether or not the final attack planned (then seen briefly at the end) on the creature was a nuclear one or not, with questions about if a digital camera that survived the attack could have survived a nuclear blast, or even the EMP. Personally, I’m in the former camp—a standard U.S. B-61 tactical nuke at a lower yield setting could, by my estimates, be sufficiently destructive enough to bother using, without completely glassing the region of the attack (and thus destroying, or shorting out, the camera). It’s even possible it was using in conjunction with conventional weapons used to _herd_ the monster towards a relatively empty (or at least, already pulverized) area before setting off the nuke.