Naked Science Forum

Non Life Sciences => Technology => Topic started by: thedoc on 07/08/2015 15:50:01

Title: Can we use pure copper to keep a bulb lit forever?
Post by: thedoc on 07/08/2015 15:50:01
Usman asked the Naked Scientists:
Is it possible that we use a simple circuit, we use battery and 2 copper wires to light up a bulb and never cut off the circuit, then the bulb will lighten up infinite? is this possible if we use pure 100% copper wire?

What do you think?
Title: Re: Can we use pure copper to keep a bulb lit forever?
Post by: chiralSPO on 07/08/2015 19:40:26
The bulb will remain lit until the battery runs out of energy to power the bulb. The material of the wires will partially determine how much of the battery's energy is wasted, and therefore how long the light will remain lit. However, even with superconducting wires (no inefficiency between the battery and the light), the bulb converts the energy stored in the battery into light energy, and so must eventually deplete the battery.
Title: Re: Can we use pure copper to keep a bulb lit forever?
Post by: evan_au on 08/08/2015 02:20:12
An old-fashioned incandescent lamp generates light because it has resistance, and the current flowing through it heats up the filament with a power: P=I2R
This power has to come from somewhere, and that is the battery. If the battery goes "flat", or you disconnect the battery, that power source is gone, and the light goes out.

There is one case where we do something like what you describe: in a medical MRI scanner. These are cooled down to very low temperatures with liquid helium, so current can flow in the wires with no resistance (R=0). This current passes through coils, which generate a strong magnetic field for peering inside your body. When the current in the coil reaches the intended level, it is possible to disconnect the power source, and the current will keep flowing in the wire, as long as the refrigeration keeps going.

The difference is that a steady magnetic field in the MRI scanner does not radiate any power (P=0), so the energy in the coil remains constant, without having to be "topped up". In contrast, the lamp filament is always radiating light and heat into the surrounding area, so you have to keep injecting more power into the filament, and you will drain the battery for this power.