Rate and Discuss: Before The Flood

[Jon Masters]

A Faraday cage is just a room whose walls are made out of metal or contain a metal mesh, so that you're surrounded by a conductor. So your car is in fact a Faraday cage. A lead lined one is no problem so long as you don't try to eat the walls ( and no thickness of lead will help you if a nuclear reactor melts down anyway)

[Si Hunt]

I quite enjoyed the complexity of this episode - new ideas are good, and seeing 'how' an adventure was set up was great. The ghosts were really well done and sinister, although in the bit where the Cass is chased by the ghost with the axe I felt oddly un-terrified - strange that this scene was largely silent when it could have done with a bit of subtle music. Not often you can say that Murray Gold underdoes things!!

The Fisher King was great when seen in the darkness of the bunker, but somewhat less impressive legging it out in the open, when he suddenly looked like a bloke in a dodgy costume. Keeping the monsters in the gloom might be a good idea!

One thing about the plot I didn't think was especially well wrapped up, and that's just HOW people turn into ghosts. Sorry, but I didn't get it. Sometimes people died in the past and their ghosts appeared in the future- other times, people died in the present and then appeared as ghosts. What were the ghosts anyway? Did the Fisher King somehow make people become the ghosts? And how, when he wasn't even in the same time zone? I'm not entirely sure how the Doctor arranged his hologram either.

So quite enjoyed this one, not the worst, although I am having misgivings about all the 2-parters this year. This story reminded me that 2 parters have always seemed rather long, grey and not very popular with the public. I'm beginning to dread a whole year of them. This would have been great as a mid-season 'thoughtful' episode but you want colourful, sparky jaunts to the past this early on, not a long complex story set in a base that you have to work out the plot to. If I were a casual, I wouldn't still be watching, and in fact I'm not overly bothered about next weeks dull looking runaround with Vikings to be honest.

So probably one of the best 2-parters, but not really one of the best Capaldi stories, and probably only just in the Top 20 stories since 2005.

Si.

[Perry Vale]

A Faraday cage is just a room whose walls are made out of metal or contain a metal mesh, so that you're surrounded by a conductor. So your car is in fact a Faraday cage.

No, a Faraday cage is designed to block electric fields, I'm not aware of any car that boasts that claim?

[Jon Masters]

http://http://www.youtube.com/watch?v=ve6XGKZxYxA

They don't advertise it but since you're surrounded by metal it happens anyway
The link is to Top Gear where they sat Hammond in a car and hit it with lightning.

[Perry Vale]

I hate to question the scientific knowledge of Richard Hammond, but I think if it was a true Faraday cage, your mobile phone wouldn't work inside the car.

[Dirk Gently]

A faraday cage is any conductive frame work that transmits electricity around a body. A car or that metal suit that David Blane used in his 'stunt' are both considered to be Faraday cages.

[Perry Vale]

https://en.wikipedia.org/wiki/Faraday_cage

A Faraday cage or Faraday shield is an enclosure formed by conductive material or by a mesh of such material, used to block electric fields.

....

The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage is heavily attenuated or blocked by the cage.

Which is why, I imagine, Clara places the mobile phone outside of the Faraday cage, and I assume, why the "ghosts" can't get in.

Experiments around Schumann resonances in humans with a fully functioning Faraday cage that blocked out all EMF caused the human lab rats to feel nausea, discomfort and extreme migraine headaches.

Can someone explain the plot point of the cage in Under The Lake/Before The Flood? I don't get it.

[Jon Masters]

From the wiki page you linked to

Faraday cages cannot block static or slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside). To a large degree, though, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation. For example, certain computer forensic test procedures of electronic systems that require an environment free of electromagnetic interference can be carried out within a screened room. These rooms are spaces that are completely enclosed by one or more layers of a fine metal mesh or perforated sheet metal. The metal layers are grounded to dissipate any electric currents generated from external or internal electromagnetic fields, and thus they block a large amount of the electromagnetic interference. See also electromagnetic shielding.

The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage is heavily attenuated or blocked by the cage.

So cars won't block mobile signals ( nor aeroplanes) because the gaps in the metal surface ie windows etc are bigger than the wavelength of the microwaves used to transmit phone signals. But it is why you have the car aerial on the outside of the car not the inside.

the episode claims the Faraday cage is there because the mining equipment runs on nuclear power, which makes no sense at all . It would have been more correct if they had claimed there was very sensitive equipment inside that needed to be shielded from external em waves.