Understanding Volts and Amps!!

[HappyHippyDad]

I'd like to understand a bit more about what actually gives you an electric shock. I think the more you understand something the safer you will be.

I have been taught that it is the current (amps) that gives you the shock, but this then confuses me with regard 12v equipment (lets say anything domestic - downlights for example using a transformer), as if the lights are 10W then:

Power = Voltage x Amps

10 = 12 x Amps

Amps = 10/12 = 0.83

If however the light were from the mains:

Amps = 10/230 = 0.04

So according to the maths a low voltage system uses more current and would be more dangerous as its amps that cause the shock. I know I'm missing something simple as this cant be right but I get a bit carried away with maths!

Could anyone explain this a little please?

 

[Silly Sausage]

You're right saying it's current that does the damage.

It's voltage that drives current through a given resistance, Ohm's Law.
So greater the voltage, greater the current, hence 12V is regarded as 'safe'.

In your lamp example, the 12V ones have a lower resistance than the 230V variety, hence larger current to give the same Power rating for both. P = IV.

 

[Chr!s]

I'd like to understand a bit more about what actually gives you an electric shock. I think the more you understand something the safer you will be.

I have been taught that it is the current (amps) that gives you the shock, but this then confuses me with regard 12v equipment (lets say anything domestic - downlights for example using a transformer), as if the lights are 10W then:

Power = Voltage x Amps

10 = 12 x Amps

Amps = 10/12 = 0.83

If however the light were from the mains:

Amps = 10/230 = 0.04

So according to the maths a low voltage system uses more current and would be more dangerous as its amps that cause the shock. I know I'm missing something simple as this cant be right but I get a bit carried away with maths!

Could anyone explain this a little please?

Human Body 1000 ohms

Voltage 11kv Current through body = 45.83 amp
Voltage 240v = 0.24 amps
Voltage 12v = 0.012 amps

 

[Brightspark2]

Think of it as the voltage is the size of the punch and the amps is how fast its coming at you...

 

[DanDobson]

My college teacher compared electricity to water flowing through a pipe.
The current is how much water there is and the voltage is the pressure behind it making it flow.
Just another simile type description to try and help you understand.

Dan

 

[Brightspark2]

My college teacher compared electricity to water flowing through a pipe.
The current is how much water there is and the voltage is the pressure behind it making it flow.
Just another simile type description to try and help you understand.

Dan

I was taught this also :smug:

 

[i=p/u]

adding on to this, are you saying its cheaper to run 12v/50w lamp ,than 230v/50w lamp...?????????????????:rockon2:

Human Body 1000 ohms
?????????????
Voltage 11kv Current through body = 45.83 amp
Voltage 240v = 0.24 amps
Voltage 12v = 0.012 amps

 

[HappyHippyDad]

I think I'm getting it! Its all to do with resistance!

At lower voltages your body has much greater resistance therefore less current will run through you.

Apparently at 25V the total body impedance of a hand to hand circuit for dry skin, large contact areas, 50 Hz AC currents would be roughly 3250 ohms.. so

current passing through you would be only 0.007A

Thankyou Chris and Archy for making me think of resistance! Brightspark2, wouldn't it be the other way around? Amps are the electrons (i.e the punch), volts the push, i.e how fast coming at you?

 

[Brightspark2]

adding on to this, are you saying its cheaper to run 12v/50w lamp ,than 230v/50w lamp...?????????????????:rockon2:

No, 12V would use more amperes...

Brightspark2, wouldn't it be the other way around? Amps are the electrons (i.e the punch), volts the push, i.e how fast coming at you?

Nope, volts size of punch, amps is how fast its coming at you. Remember its not a fact just a similie, dont look into it too much lol...

 

[i=p/u]

so cost more to run...................

No, 12V would use more amperes...



Nope, volts size of punch, amps is how fast its coming at you. Remember its not a fact just a similie, dont look into it too much lol...