Nonlinear Conduction | Ohm's Law | Electronics Textbook
Conductor is also known as a resistor; An ideal conductor is a material whose resistance does not change with temperature. For an ohmic device,. V = Voltage . The light bulb does not have a linear relationship. The resistance of the bulb. Incandescent light bulbs, in addition to providing illumination, are The resistivity-temperature relation for a tungsten bulb filament is well known and the data. to light a bulb; to experimentally show that an incandescent light bulb does A fact mentioned only briefly in the text is that the resistivity is temperature dependent. If a graph of current vs. potential difference is linear, then the circuit element.
This amounts to figuring out where on the bulb the electrical contacts are. Simply touch the alligator clips to those contacts wherever you think they are. If the bulb doesn't light but you feel the battery getting warm, you've created what's called a short circuit. That means you're connecting the battery to the same point on the bulb.
This effectively bypasses the bulb and would quickly run down the battery if you left it connected that way.
- Electric circuits
- Resistance of Light bulb filaments as temperature goes up?
Once you're successful in lighting the bulb, sketch a large diagram showing the bulb and the two points on the bulb that you touched with the alligator clips.
If no matter what you do, you can't get the bulb to light, your battery may be too weak.
The filament lamp
In that case, try using two batteries in series. Having determined how to light a bulb, do so again, but reverse the positions of the alligator clips where they touch the bulb.Light Bulb - Resistance and Diff Resistance
The point is to make the current flow the opposite direction. Do you see a difference from the results of step 1? Did you expect to? Maybe you thought the above exercises were a bit too simple for high-school students. However, studies show that many college physics students don't know how to light a bulb when it's not in a socket. Screw the light bulb into its holder now. There are two clip contacts on the holder. Connect an alligator clip to each one. Touch the other ends of the alligator clips to the ends of a battery.
If your battery is fresh, the bulb should light, although it will be weak.
If the bulb doesn't light, make sure it's screwed completely into the holder. From now on you'll leave the bulb in its holder. At this point, you should have your bulb in its holder connected to a single battery.
Add a second battery in series with the first as shown to the right. Repeat with 3 batteries. Describe what you observed as you added batteries.
What you're doing when you change the number of batteries is changing the amount of power dissipated by the bulb. Explain your observations using circuit concepts and relationships. The purpose of this question is to give you practice in using standard physics vocabulary such as potential difference, current, resistance, power and energy.
When you talk about potential difference, say potential difference across the bulb.
BBC - GCSE Bitesize: The filament lamp
Similarly, you would speak of current in the bulb. The goal is to explain clearly without making nonsensical or ambiguous statements about electrical circuits. Don't rely on equations to make your argument for you. Give your argument in paragraph form. Determining whether the bulb obeys Ohm's Law Before making resistance, voltage, and current measurements, review the multimeter tutorial for how to connect the probes to the meter and to the circuit.
First, you'll measure what we call the room-temperature resistance of your light bulb, that is, the resistance when the bulb isn't lit. Ideally, you need to know the resistance of your bulb when no current is passing through it.
However, when you connect your meter to the bulb to measure the resistance, the meter passes a small current through the bulb. This will heat the filament slightly and change its resistance. In order to minimize this effect, don't leave the meter connected for a long period of time while you measure the resistance.
Characteristics of a Light Bulb
Just hold the leads in place long enough to get a stable reading. Once ionized, air and other gases become good conductors of electricity, allowing electron flow where none could exist prior to ionization. If we were to plot current over voltage on a graph as we did with the lamp circuit, the effect of ionization would be clearly seen as nonlinear: The graph shown is approximate for a small air gap less than one inch. Incidentally, this is the reason lightning bolts exist as momentary surges rather than continuous flows of electrons.
The voltage built up between the earth and clouds or between different sets of clouds must increase to the point where it overcomes the ionization potential of the air gap before the air ionizes enough to support a substantial flow of electrons. Once it does, the current will continue to conduct through the ionized air until the static charge between the two points depletes.
Once the charge depletes enough so that the voltage falls below another threshold point, the air de-ionizes and returns to its normal state of extremely high resistance.
Many solid insulating materials exhibit similar resistance properties: Once a solid insulating material has been compromised by high-voltage breakdown, as it is called, it often does not return to its former insulating state, unlike most gases. It may insulate once again at low voltages, but its breakdown threshold voltage will have been decreased to some lower level, which may allow breakdown to occur more easily in the future.
This is a common mode of failure in high-voltage wiring: Such failures may be detected through the use of special resistance meters employing high voltage volts or more. There are circuit components specifically engineered to provide nonlinear resistance curves, one of them being the varistor. Unlike the breakdown of an insulator, varistor breakdown is repeatable: A picture of a varistor is shown here: There are also special gas-filled tubes designed to do much the same thing, exploiting the very same principle at work in the ionization of air by a lightning bolt.
Some devices actually experience a decrease in current as the applied voltage increases. Most notably, high-vacuum electron tubes known as tetrodes and semiconductor diodes known as Esaki or tunnel diodes exhibit negative resistance for certain ranges of applied voltage.
For the benefit of the student, however, we will assume that resistances specified in example circuits are stable over a wide range of conditions unless otherwise specified. I just wanted to expose you to a little bit of the complexity of the real world, lest I give you the false impression that the whole of electrical phenomena could be summarized in a few simple equations. The resistance of most conductive materials is stable over a wide range of conditions, but this is not true of all materials.
Any function that can be plotted on a graph as a straight line is called a linear function. In circuits where resistance varies with changes in either voltage or current, the plot of current over voltage will be nonlinear not a straight line. A varistor is a component that changes resistance with the amount of voltage impressed across it. With little voltage across it, its resistance is high.