Stupid question about electricity...

stilernin

Can someone tell me for how long electricity can be 'stored' in the lead between the appliance and the socket?

I sometimes switch off my radio by using the 'standby' switch and sometimes by flicking the switch at the socket. (Don't ask me why??).

Recently I noticed that if I switch off at the radio and then at the socket, I can switch the radio back on for 1-2 seconds by only restoring the standby switch.

This is idle curiosity as I don't really understand electricity, although if by using 'standby' alone I am using electricty unecessarily, it would be good to know....:money:

........... if I have posted this in the wrong place please could someone move it?

espresso

stilernin wrote:

Can someone tell me for how long electricity can be 'stored' in the lead between the appliance and the socket?

It is not possible to store AC electricity in the lead between the appliance and the socket. The effect that you are experiencing is due to a DC voltage being temporarily stored in the appliance, until it is used up.

Avoriaz

Espresso is correct.

Your radio, like most similar electronic devices, takes 230 volt alternating current from the mains. It converts this electricity to a much lower (maybe 12 volts or so) direct current using transformers, rectifiers and capacitors and other electronic devices.

Capacitors function as a storage reservoir for power. One of their functions is to smooth out fluctuations in the flow of electricity. When you switch off at the mains, a few seconds worth of power remains in the capacitors.

Some devices such as TVs can actually contain dangerously high voltages long after you have unplugged them because of the amount of temporary power stored in capacitors.

kittiwoz

Electricity isn't stored in the lead. It'll be stored in capacitors in the radio. I think using standby is supposed to help protect the components in the radio that get worn out more by being switched on and off but it does use a small amount of power. Not very much though.

If you are interested this is a basic desription of how electricity works. The circuit is made of a conductive metal (usually copper) which has free electrons in it. These are electons which can move through the material rather than orbiting a particular nucleus. The electrons have a negative charge and when you apply a voltage across the wire it causes the electrons to move towards the positive terminal as opposites attract and like charges repel one another. However we think of electric current as flowing from the possitive to the negative terminal, although physically that isn't what happens, simply because this was established as the convention before it was understood what was physically causing the current to flow. The current is the rate at which the charge (measured in coulombs) flows [Q(charge)=I(current)*t(time)] so the more free electrons and the faster they move, the greater is the current. That is why a wire which is made of a material with less free electrons, or a thinner wire which also has less free electrons per unit length will be less conductive and so be said to have a greater resistance. For example if the wire has half as many free electrons per unit length it has twice the resistance and if the same voltage is applied the current will be halved so to produce the same current would require double the voltage [V(Voltage)=I(current)/R(resistance)]. The energy transfered is charge times voltage [E=Q.V] so the power (in Watts) which is the rate of energy transfer is current times voltage [P=Q.V/t, Q=I.t :. P=I.V].

Electricity isn't stored in a wire. It is like water flowing in a closed system of pipes where all the pipes are always full of water. Opening a valve (i.e switch) between two pipes won't make the water flow unless you turn the pump on to create a pressure difference (i.e. apply a voltage) and when you do the water (electrons) doesn't start flowing at one place and then move along like it would in an empty channel it starts moving at every point in the system at the same time.

Capacitors are rather like tiny rechargeable batteries although they work differently. They have two conductive plates seperated by a thin insulator (and normally rolled up like a Swiss roll so as to get a big surface area within a small space). When you apply a voltage across a capacitor the plate connected to the negative terminal of the voltage supply recieves electrons and becomes negatively charges while the plate connected to the positive supply looses electrons and becomes positively charged. This gives rise to a voltage across the capacitor which can then be used to cause a current to flow in a circuit. Capacitors can't store much charge compared to batteries which is why they can only power your radio for a couple of seconds. (Therefore they need to store it at high voltage to produce more power which is why, as Avoriaz says, they can contain dangerously high voltages in some appliances). They have loads of uses but the ones which allow you to switch your radio on for a couple of seconds when it has been switched off at the plug will be part of a smoothing circuit. What that does is that you have an AC input to the radio which will pass through a rectifier which stops the current from reversing but doesn't stop it fluctuating between maximum and zero and so there is a smoothing circuit which relies on a capacitor after the rectifier which reduces the fluctations so you get a fairly steady voltage (though still with some ripple).

stilernin

Phew........ kittiwoz....... thanks for that. I have read your explanation a few times and have a greater understanding than before. Glad that there wasn't a test at the end!! :rotfl: :rotfl:

expresso and Avoriaz, thanks too.

So as I understand it, it is a balance between using a small amount of electricity by not switching off at the socket and spending on a new radio sooner by not using the standby facility? There isn't actually an 'off' switch on the radio.

Goodness knows why I am even thinking about this........ it was just something I suddenly noticed.

Being a 'woman of a certain age' I am not about to learn to be an electrician now!!

Thanks to you all again though.

Avoriaz

stilernin wrote:

…it is a balance between using a small amount of electricity by not switching off at the socket and spending on a new radio sooner by not using the standby facility? There isn't actually an 'off' switch on the radio…Being a 'woman of a certain age' ..

Don’t worry about it. I prefer not to use standby where possible as it does use a bit of electricity. I switch my portable radios on and off many times a day and they are all many years old.

But if you prefer to use standby, the amount of electricity used is negligible.

Have you considered using your hot flushes to generate electricity?

rygon

I always thought that standby took up quite a bit of electricity

stilernin

Avoriaz wrote:

Don’t worry about it. I prefer not to use standby where possible as it does use a bit of electricity. I switch my portable radios on and off many times a day and they are all many years old.

But if you prefer to use standby, the amount of electricity used is negligible.

Have you considered using your hot flushes to generate electricity?

Luckily I only get HFs towards the end of a good bottle of red.... cheers!:beer:

djohn2002uk

Avoriaz wrote:

Some devices such as TVs can actually contain dangerously high voltages long after you have unplugged them because of the amount of temporary power stored in capacitors.

Most of your post is basically correct but not this quote. The high voltages that are residual in CRT TVs is not from capacitors as such but to the tube itself which has thousands of volts applied to it so that it attracts the electrons from the cathode at high speed. The tube acts like a capacitor and ca hold its charge for days or even weeks.
The dangerous part of the tube is the anode where the high voltage lead connects on the back of the tube and should always be discharged before working on it.

JS2006

I read stand-by used 25% of the power you'd normally use if the device was on full power

Avoriaz

djohn2002uk wrote:

Most of your post is basically correct but not this quote.

I was just trying to make it as simple as possible.

I couldn’t possibly compete with kittiwoz’s PhD thesis.