why is the resistence like this?? and can you measure the resistence of a light bulb when hot and why??
2007-12-12 01:23:14 · 3 answers · asked by Anonymous in Science & Mathematics ➔ Physics
The resistance cold is much lower than hot. This can be proved by measuring it cold with a ohmmeter then powering it up and measuring it hot by measuring the voltage and current and using ohms law.
2007-12-12 02:18:44 · answer #1 · answered by Poor one 6 · 0⤊ 1⤋
Well there is a current carrying thread of wire in light bulbs called filiments. Resistance in a current carrying wire is dependent on the temperature. What happens is that the particles that make up the wire are moving around with some average velocity, and they are constantly zig zagging and colliding with each other. The more they move around, the more they collide and hence the slower the current making it all the way through the wire (Instead of going straight through the wire they will colide more with other particles slowing down its progress). As you increase the temperature you will increase the collision rate and you current will move slower, in other words you increase the resistance.
Measuring the resistance of the filament when the light bulb is not connected to a voltage is easy. Just get a Multimeter or voltmeter...put it on the ohm setting and place them on opposite sides of the filament. When the light buld has a voltage connected you should not measrue the resistance..youll probably get a wrong readingd
2007-12-12 01:36:08 · answer #2 · answered by Brian 6 · 2⤊ 0⤋
To measure the resistance when the bulb is lit, measure the current (I) it draws and the voltage. Then use Ohm's law: R = V / I
2007-12-12 01:57:43 · answer #3 · answered by Chuck 6 · 0⤊ 1⤋