current

[spoonse]

has anyone heard of resonance in electric currents and the effects of this on the ear?

 

[ban-all-sheds]

Resonance?

I guess if you had an object which had:

a) a susceptibility to being influenced by the EMF from a cable

b) a resonant frequency of 50Hz, or an overtone thereof

then it might resonate due to an electric current, and you might hear it.

But other than that I'm not sure what you mean by "resonance in electric currents"....

 

[Biggles..]

Resonance or Resonant Frequency is a term used in electrical engineering and from memory (old HND theory) is to do with inductance(XL) and capictance(XC) in circuits. There was an old formula to caculate it which was 1/(2pieRootLC)=resinant frequency.

If the capacitance and inductance(reactances) of a circuit are equal then no current will flow by virtue of the total impedance being infinate.

We used it when designing oscillators and receivers for radars.

 

[ColJack]

you sure that's right..?

I thought current would still flow, but it would be purely resistive and would be in phase..

that's the reason for putting capacitors on inductive lighting, to bring the current back into phase with the voltage.. power factor correction..


[code:1] XC = ___1____
2xPIxFxC[/code:1]

[code:1]XL = 2xPIxFxL[/code:1]

 

[spoonse]

An emf from a cable or cables?what it is ,ive a shed thats been wired up and every time i go into it i get a sensation in both ears and was wondering if maybe there was such a thing as exposure to anything such as this...just ruling things out really, its a weird one i know

 

[bernardgreen]

What is the sensation ? And do you still sense it when all lights and equipment are turned off ?

Some light fittings with transformers and/or dimmers emit low levels of noise, ordinary flourescents and normal transformers will sound at 50 or 100 Hz. dimmers and electronic " transformers" can make a range of sounds from 100 Hz to high frequencies above the range of normal hearing. Some high frequency sounds are not heard but can in some people create an "awareness" of discomfort in the ear.


A properly wired installation should not created any significant magnetic effects round cables as the majority of cables have equal and opposite currents in the wires that magnetically cancel each other out.

 

[tim west]

There were cases around the 70's when people were complaining about picking up radio signals in tooth fillings, these were attributed to taxi firms transmitters, if the stories were true then there is no reason to suppose that an electrical field of sufficient power(doesn't have to be RF) couldnt do likewise, have you any metal fillings?

 

[spoonse]

unfortunately i do have fillings and its intresting what you say about radio waves.The outside walls are covered in e.m.l to accomodate the rendering,i don't know but there may be a situation where its acting as an antenna maybe?the sensation feels like a warming in both ears and this lasts for a couple of days and it only occurs when i'm in the shed,have had ears checked by gp and they're ok but it starts all over again when i'm in the roomspace of the shed

 

[Adam_151]

unfortunately i do have fillings and its intresting what you say about radio waves.The outside walls are covered in e.m.l to accomodate the rendering

The expanded metal lathing will reduce the strength of external radio waves rather than concentrate them, its known as the faraday effect and is the same reason why you can sometimes have a diificult time getting a decent signal on a mobile telephone in a metal framed building, although consequency the phone might increase its own ERP as a result! (and as its right close to you head, it might be much worse than the background stuff from the local transmitter)

 

[Biggles..]

you sure that's right..?

I thought current would still flow, but it would be purely resistive and would be in phase..

that's the reason for putting capacitors on inductive lighting, to bring the current back into phase with the voltage.. power factor correction

Capacitors are used in this way to ensure that the PFC remains as close to 1 as possable to avoid unwanted losses but the capactive load is never calculated to resonate.

if XL and XC are equal from the formulas above, when used in the formula for parallel impedances it becomes impossable to divide 1 by 0 making the parallel impedance undefined(open circuit allowing no current to pass)

Tank circuits(inductive and capacitive load in parallel) can be used as a crude ac block when resonnating.

Its took a while to dig all this rubbish out of my old notes.

 

[spoonse]

Blimey i'm a little blinded by your superior knowledge and thanks to all,i guess the e.m.l is no threat then,which is a relief ,i'll try unplugging the connection to the house and see how that goes

 

[Stoday]

Wound magnetic components, such as chokes, transformers and motors hum because of resonance effects. The resonance is mechanical and is created by magnetostriction (which makes iron change shape) and current forces (which change forces on copper conductors).

Fault currents can induce surprisingly high forces on conductors; I have seen windings stripped out of stator slots and copper busbars bent like Uri Geller's spoons.

 

[Mud Hut]

Some light bulbs can "sing" when connected to a dimmer switch. This is probably caused by ringing of the element because the dimmer circuit chops the mains and introduces high order harmonics.

 

[securespark]

Some light bulbs can "sing"......high order harmonics.

Like the BeeGees?

 

[Mud Hut]

Like the BeeGees?

Nah, more like ELO