BBC Bitesize - GCSE Physics (Single Science) - Current, voltage and resistance - Revision 4
Current, Resistance, Voltage, and Power. Current Current is a measure of the flow of The equation V = IR means that the potential difference, or voltage, across a resistor can be found This relation can be found from the formula for power. Calculator for solving resistance given voltage and power in the Ohm's Law The electrical relationships between resistance (R), current (I), power (P) and which allows the current of one ampere under a potential difference of 1 volt. Charge, Current & Potential Difference in circuits. Conventional current flows around a circuit from the positive (+) side of the cell potential difference equation Resistance (W) – is the ratio of potential difference across a component to the.
And what is resistance? And what are the units for them so that we can make sense of this? So to get an intuition for what these things are and how they relate, let's build a metaphor using the flow of water, which isn't a perfect metaphor, but it helps me at least understand the relationship between voltage, current, and resistance.
So let's say I have this vertical pipe of water, it's closed at the bottom right now, and it's all full of water.
Charge, Current & Potential Difference
There's water above here as well. So the water in the pipe, so let's say the water right over here, it's gonna have some potential energy.
And this potential energy, as we will see, it is analogous to voltage. Voltage is electric potential, electric potential. Now it isn't straight up potential energy, it's actually potential energy per unit charge.
So let me write that.
- Current, Resistance, Voltage, and Power
- Power, current and potential difference
- Introduction to circuits and Ohm's law
Potential energy per unit, unit charge. You could think of it as joules, which is potential energy, or units of energy per coulomb.Difference Between Voltage, Current and Power in Hindi.
That is our unit charge. And the units for voltage in general is volts. Now, let's think about what would happen if we now open the bottom of this pipe. So we open this up. Well, the water's immediately gonna drop straight down. That potential energy is gonna be converted to kinetic energy. And you could look at a certain part of the pipe right over here, right over here. And you could say, well, how much water is flowing per unit time?
And that amount of water that is flowing through the pipe at that point in a specific amount of time, that is analogous to current. Current is the amount of charge, so we could say charge per unit time.
Introduction to circuits and Ohm's law (video) | Khan Academy
Q for charge, and t for time. And intuitively you could say, how much, how much charge flowing, flowing past a point in a circuit, a point in circuit in a, let's say, unit of time, we could think of it as a second.
And so you could also think about it as coulombs per second, charge per unit time. And the idea of resistance is something could just keep that charge from flowing at an arbitrarily high rate. And if we want to go back to our water metaphor, what we could do is, we could introduce something that would impede the water, and that could be a narrowing of the pipe. And that narrowing of the pipe would be analogous to resistance.
Current, Resistance, Voltage, and Power
So in this situation, once again, I have my vertical water pipe, I have opened it up, and you still would have that potential energy, which is analogous to voltage, and it would be converted to kinetic energy, and you would have a flow of water through that pipe, but now at every point in this pipe, the amount of water that's flowing past at a given moment of time is gonna be lower, because you have literally this bottleneck right over here.
So this narrowing is analogous to resistance. How much charge flow impeded, impeded. And the unit here is the ohm, is the ohm, which is denoted with the Greek letter omega. So now that we've defined these things and we have our metaphor, let's actually look at an electric circuit. So first, let me construct a battery. So this is my battery.
And the convention is my negative terminal is the shorter line here. So I could say that's the negative terminal, that is the positive terminal. Associated with that battery, I could have some voltage. And just to make this tangible, let's say the voltage is equal to 16 volts across this battery. And so one way to think about it is the potential energy per unit charge, let's say we have electrons here at the negative terminal, the potential energy per coulomb here is 16 volts.
These electrons, if they have a path, would go to the positive terminal. And so we can provide a path.
Let me draw it like this. At first, I'm gonna not make the path available to the electrons, I'm gonna have an open circuit here. One Ohm is equal to one Volt per Ampere, Resistance depends on temperature in the same way as resistivity, This formula requires R0, the resistance at a reference temperature T0. A resistor is a device that is used in electric circuits, and has a certain fixed resistance. Resistors are made by choosing a piece of material with a certain resistivity, length, and area, and wrapping it in an insulator with wires leading out of each end.
In circuit diagrams, it is represented with the symbol, Voltage Voltage is a difference in electric potential between two points. A voltage source is a device used in electric circuits that has a fixed potential difference between its ends.
A voltage source can be a battery, or another source of direct current with a fixed potential difference. In circuit diagrams, it is represented with the symbol, If the ends of a voltage source are connected through a circuit with any number of resistors or other components, a complete circuit is formed, and current can flow from one terminal to the other.
If current is flowing, it will be the same on both terminals of the voltage source. For an ideal source, the electromotive force is equal to the voltage difference, Real sources like batteries are not ideal, and so there is some amount of internal resistance.
If the internal resistance of a battery is r, then the voltage difference across the battery is, This is also called the terminal voltage of the battery. Power Power P is a measure of the rate at which energy is delivered or used by a circuit element.