How fast is electricity?

78 views

Why does it sometimes seem instant and sometimes it seems to take time for something to work? For example, if I leave my hoover switched on and plug it in, it seems to start immediately, but when I switch the plug off for my tv the stand by light takes a few seconds to go off?

Edit: thanks for the explanation guys, seems like the answer I was looking for was some appliances use capacitors.

In: Physics

electrons actually move very slow. But they sort of ‘bump into each other’ and push electrons to the device. This is called drift velocity. Electromagnetic waves move at the speed of light. The electricity you’re referring to is the ‘signal velocity’ and is faster than drift, but slower than speed of light

Source google: This makes the observable speed of electricity about the same as the speed of light: 186,000 miles per second, or 299,792 km/s. With this known a simple calculation gives the speed of electrical activity through a wire stretching around the entire Earth at well under one second, about 0.134 seconds.

The speed of an electrical signal in a wire depends on the wire but we talk double-digit percentage of the speed of light in a vacuum. On something like an overhead power wire, it is in the 90-95% of the speed of light in a vacuum. In electrical computer networks cable, it is around 66% of the speed of light in a vacuum that also happens to be the speed of light in optical fibers. Light travels slowly in a medium like glass than in a vacuum.

The speed of electricity can also be the speed electrons move in a wire. That speed is quite slow we talk about speed around 1 meter per hour in the typical electrical system.

That is in a way the speed of electricity but is not the explanation to your question.

​

The LED on the TV turn one after a few seconds because the power supply contains capacitors that can store electrical energy. You can compare to statical electricity that can get if you rub some material together and can be discarded with a small electrical spark. So electrical charge can be stored. You can in some way look at capacitors and low capacity rechargeable batteries.

The capacitors are used in the conversion of the AC(alternating current) in the wall outlet to the DC (direct current) that the TV use. If the power usage is quite low like a single LED the power stored in the capacitor can have enough energy to power for a short time even when you disconnect it from the wall outlet.

The power supply has a dedicated component to discharge capacitors when you unplug them, if you did not include any you could get an electrical shock from touching the pins you plug into the wall after you unplugged it.

A hoover will have a motor that is directly powered from the wall outlet and there is no component that can store enough energy to power it for any noticeable time after you turn it off.

So the speed of electricity is high or quite low depending on what you look at, but not relevant to the question. The explanation is that electrical energy can be stored in components in a device and they can contain enough to power it for a short time if not a lot is used.

Electricity is fast. Very fast. As you’ve been told, close to light speed.

What you observe is not really related to the “speed” of electricity. Electronics in the TV include some components that store a small amount of charge (“electricity”). When the TV is in standby it uses only a small amount of it, so when you unplug it, it takes some time for the electricity stored to be consumed. When you turn on something, in most cases the power is instantaneously on, but depending on the device there is maybe some kind of processor doing stuff to “boot” the device, just like a PC or smartphone.

Your Hoover motor is directly connected to the power supply.

The little LED showing the standby status of the TV is not

Electricity works because charged electrons are made to move by the electromagnetic field, and then pass on that movement energy to other things. A couple of answers mention electrons ‘bumping into each other’ to move down wires, which is incorrect.

Imagine you have a pool table with balls (not touching) on the surface, and you tip up one end of the table. The balls will start to roll down, all at the same time (in fact there is an imperceptible delay in moving those at the far end, which you could imagine seeing if the table was rubbery).

This is like what turning on a switch does for electrons. The electrons don’t travel near the speed of light, but the change in the electric field which moves them (tipping up the table) does.

As other answers have suggested, you are thinking about capacitors, that store charge, taking some time to drain once a device is turned off. This can sometimes happen quite slowly due to the resistance of components, like if the pool table above was sticky.