Also, which one increases when the other decreases, and vice versa. Finally, say you have an LDR in a street lamp, when is the resistance high, during day or night, and why? Then what happens with the current?
2006-10-01 05:15:20 · 6 answers · asked by mbchelsea 1 in Science & Mathematics ➔ Physics
With the same voltage, increasing the resistance decreases the current.
As for LDRs, they have a high resistence when in the dark. So in a street light, detecting a low current through (or high voltage across) an LDR means that is is dark and it's time to turn the street light on.
You would confuse the circuit if the street light was allowed to illuminate the LDR
2006-10-01 05:22:06 · answer #1 · answered by amania_r 7 · 0⤊ 1⤋
V = IR; where V is the potential in volts, I is the current in amps, and R is the resistance in ohms.
R is called resistance because it resists the free flow of electrical current. Thus as R is increased, the flow of current (I) slows down unless V, the voltage, is increased to compensate for the increase in R.
A great analogy, which you can relate to and visualize, is that of a garden hose, which is like a wire. In the hose, the flow of water is like the flow of electrical current. In the hose, the spigot at the house is like the resistance R. And the water pressure is like the voltage.
You can slow down the flow of water out of a hose by shutting the spigot to almost closed. Because the water pressure behind the spigot (on the house side) is constant, the increased resistance of the spigot, slows the flow of water. Similar thing happens in a wire when you increase the resistance R.
Like in a hose, you can make the resistance in a wire so high that the current I stops altogether. For example, if you break the wire, which is what you do when opening an electrical switch. the electrical current will stop flowing. That's what happens when a street light is turned off during the day. It's switch is turned off and the resistance of that break in the wire is so great that the flow of current I stops.
Like in a hose when the spigot is completely closed, the current stops flowing, but the pressure (voltage in a wire) is still there behind the spigot (resister in a wire).
2006-10-01 06:10:59 · answer #2 · answered by oldprof 7 · 0⤊ 0⤋
V = I / R.
V = Voltage
I = Current
R = Resistance
When voltage is constant Increasing on decreases the other.
A LDR (light dependent resistor) has greater resistance in greater light. Therefore it allows more current in less light. Others have confused this with a photo-voltaic cell that produces current when struck by light.
2006-10-01 06:39:40 · answer #3 · answered by STEVEN F 7 · 0⤊ 0⤋
a piece of glass has almost infinite resistance, so almost no current flows through it.
a piece of silver has almost no resistance, so almost infinite current flows through it.
easy way to remember, resistance is a measure of how much an object will RESIST the flow of electricity.
part 2: Most photocells have lower resistance when light hits them, so more current during the day.
2006-10-01 05:27:52 · answer #4 · answered by disco legend zeke 4 · 0⤊ 1⤋
V=IR
V= POTENTIAL DIFFERENCE
I= current
R= resistence
if V is same then increasing resistance decreases current
2006-10-01 05:35:56 · answer #5 · answered by Anonymous · 0⤊ 1⤋
current is proportional to 1/R
or I = V/R
2006-10-01 05:17:15 · answer #6 · answered by Dr M 5 · 0⤊ 0⤋