[katieHaylor (OP)]

David asks:

Can an electrical field be directed or targeted at an object? If so lets say about 100 yards. if so can it be blocked?

What do you think?

[vhfpmr]

A radio transmitter produces an electromagnetic field, and a directional antenna will point it in a particular direction. Large (in relation to the wavelength) objects will create a shadow in the field on the lee of the object, particularly if they're metal, but a screened room (Faraday cage) will shut out the field completely:
https://th.bing.com/th/id/R80608c82da7b368987146ef832b487f3?rik=6IdIZXku%2f%2bv7Jg&riu=http%3a%2f%2fi.ebayimg.com%2f00%2fs%2fMTAyNFgxMjgw%2f%24(KGrHqFHJBcE-d(-K6qTBPqy!suH3g%7e%7e60_35.JPG&ehk=ubKMWvhmP9%2fntIdDv3WwicgHWBidd6Lp5rP6Yo5oRyY%3d&risl=&pid=ImgRaw

[CliffordK]

The electromagnetic spectrum is very broad from radio waves to microwaves to IR to light to UV to X-Rays to gamma rays.

What will work for one won't necessarily work for another. 

Yet, there are many ways to either absorb, reflect, or focus many parts of the EM spectrum.

Your car headlight can focus a beam of light 100 yards down the road.

A parabolic reflector can reflect whatever you choose from radio waves to light on a much smaller receiver.

[Bored chemist]

It's also important to consider the asymmetry here.
If you spend £100,000 on a military laser or microwave source and point it at me, I can defeat it by hiding behind a £10 leaky central heating radiator  bought at the local scrap dealer.

[Kryptid]

I recall reading somewhere that electrostatic fields cannot be blocked. If you did have such a material, it would allow for the creation of a perpetual motion machine because it would allow you to separate opposite charges with arbitrarily low energy input.

[alancalverd]

Any conductor will block an electrostatic field. That's the principle of the Faraday cage: there is no electric field inside a conductive shell.

[Kryptid]

Any conductor will block an electrostatic field. That's the principle of the Faraday cage: there is no electric field inside a conductive shell.

So how is a perpetual motion machine scenario avoided? Is there some kind of energy cost to putting a charged object inside of a Faraday cage that would equal the energy one could gain by separating the charges with minimal energy input?

[Bored chemist]

There is certainly an energy cost to taking a charged object out of a conductive container (or even just away from a conductive surface.)

[Kryptid]

There is certainly an energy cost to taking a charged object out of a conductive container (or even just away from a conductive surface.)

Ah. I suppose that's how the perpetual motion machine is foiled.

[Bored chemist]

There is certainly an energy cost to taking a charged object out of a conductive container (or even just away from a conductive surface.)

Ah. I suppose that's how the perpetual motion machine is foiled.

Yes, but-more importantly, it lets you stick balloons to the ceiling.

[acsinuk]

You can shield electrostatic fields with a Faraday cage but not magnetic field particularly low frequency areas of vibrating flux.

[alancalverd]

I have installed active and passive magnetic field shielding in various MRI facilities. In the most spectacular case the client had sited an MRI unit adjacent to an underground railway, where we were challenged by a room full of mechanical vibrations and electrical and magnetic fields that changed with a frequency spectrum from "every 10 minutes" to megahertz. 

[Eternal Student]

David asks:

Can an electrical field be directed or targeted at an object? If so lets say about 100 yards. if so can it be blocked?

What do you think?

   I think you need to ask this David person why it seems like he's asking for instructions on how to build a weapon.

[alancalverd]

He's not alone in this. We have entire government laboratories devoted to the same end.

[Colin2B]

   I think you need to ask this David person why it seems like he's asking for instructions on how to build a weapon.

I think he is asking how to block a perceived weapon, probably by using something better than a tinfoil helmet.

[Bored chemist]

He's not alone in this. We have entire government laboratories devoted to the same end.

How much can I bill them as a consultant?

It's also important to consider the asymmetry here.
If you spend £100,000 on a military laser or microwave source and point it at me, I can defeat it by hiding behind a £10 leaky central heating radiator  bought at the local scrap dealer.

[evan_au]

Can you block an electric field?...say about 100 yards

If you have a point-source of an electric field (say, the charged ball on top of a Van de Graaf generator), the electric field decays rapidly with distance - like an inverse-square law. So it doesn't make much of a dangerous weapon for someone 100m away.

If you have a linear source of an electric field (say a high-voltage DC power line), the electric field decays more slowly with distance - more like 1/distance. This extends further, but the best defence is to just walk away.

If you have a plane source of an electric field, and you are between the + & - plates, then the field is uniform, and it can be quite dangerous.
- But this is not a weapon that can be fired from 100m away - you actually need to be inside the weapon.
- It becomes dangerous if you touch both plates of the weapon - it only takes about 30mA of the wrong frequency to stop your heart beating
- But provided you don't actually come in electrical contact with the plates, you have the breakdown voltage of air in series with your own somewhat salty bag of water. It is only when the voltage exceeds the breakdown voltage of air (around 700,000 Volts per meter) that a dangerous current can flow.
- This is why a few people per year are killed by walking into the charged parallel-plate weapon that is a storm cloud above the ground. The surprising thing is that some people actually survive the experience of being struck by lightning!
- The best protection is to sit inside a metal car (Faraday cage), or to erect an earthed  lightning rod (and [/i]not[/i] a lightning rod that you hold in your hand, like an umbrella or golf club).

A static electric field would not make a great weapon
- and a static magnetic field would make an even worse weapon (unless you had ferromagnetic implants in your body)
- which is why the responses above quickly jumped onto electromagnetic fields like lasers, X-rays and microwaves, which can be focused to some extent, and can propagate off "to infinity"
- There is a limit on how well electromagnetic waves can be focused; beyond that, it starts to follow an inverse-square law, like a point electric field.
- The proverbial "tinfoil hat" will reflect many of these electromagnetic waves, so there is a cheap and effective defence.

[wolfekeeper]

You can shield electrostatic fields with a Faraday cage but not magnetic field particularly low frequency areas of vibrating flux.

Low frequency magnetic fields can be shielded with (laminated) iron; provided you avoid saturating it with too much flux it's a brilliant at shunting magnetic fields around a region/the world you want to protect, but only up to a certain frequency. But you can build a Faraday cage that can deal with the remaining frequencies.

[Eternal Student]

The proverbial "tinfoil hat" will reflect many of these electromagnetic waves, so there is a cheap and effective defence.

   I can't see any answers based on refraction rather than reflection.

   Wearing a tin hat is just silly.  Cover yourself with a thick layer of Vaseline to help refract glancing rays.

[alancalverd]

He's not alone in this. We have entire government laboratories devoted to the same end.

How much can I bill them as a consultant?

Depends on the weapon. The Faraday cage patent expired ages ago, but if you can offer significant protection for infantry or civilians against nuclear or biological attack, keep bugs out of the internet, unjam radio transmissions, or prevent aircraft and missiles from being vaporised  by lasers (the US navy has a good demonstrator) or just hit by other flying objects, you can earn a good salary and pension.  Keeping bombs away from ships is also desirable.