# Electricity current and circuit questions

• Lim Y K
In summary: Electric potential difference is the difference in voltage that exists between two points in a circuit.
Lim Y K
may I know if there will be potential difference if there is no resistor in a circuit? If the positive terminal of a battery has a high potential in terms of conventional current, then in electron flow, does it mean that the negative terminal has a high potential?

There are lots of ways to cause a potential difference in a circuit other than a resistor.

Lim Y K said:
may I know if there will be potential difference if there is no resistor in a circuit? If the positive terminal of a battery has a high potential in terms of conventional current, then in electron flow, does it mean that the negative terminal has a high potential?
Electrons have high potential energy (not potential) near the negative terminal compared to the potential energy near the positive terminal, which is why electrons drift from the negative terminal to the positive terminal, giving a conventional current in the opposite direction.

In the case of a short circuit, batteries, capacitors, generators, ect, have their own internal resistance.

Chandra Prayaga said:
Electrons have high potential energy (not potential) near the negative terminal compared to the potential energy near the positive terminal, which is why electrons drift from the negative terminal to the positive terminal, giving a conventional current in the opposite direction.

May I know what do you mean by "high potential energy (not potential)"?

Lim Y K said:
may I know if there will be potential difference if there is no resistor in a circuit? If the positive terminal of a battery has a high potential in terms of conventional current, then in electron flow, does it mean that the negative terminal has a high potential?

The absolute potential is irrelevant, it is the difference in potential between two points that matters. The difference in potential between the two terminals of a battery is equal to the voltage of the battery. It doesn't matter if you think of the positive as being at +9 volts and the negative at 0, or the positive at 0 volts and the negative at -9.

Note that it doesn't matter whether you use conventional or electron current, the potential of the terminals doesn't change.

Lim Y K said:
May I know what do you mean by "high potential energy (not potential)"?

Potential energy is the the amount of energy a charge has by virtue of its location relative to other charges and/or sources of electric and magnetic fields. An electron at the negative terminal will feel a force that moves it towards the positive terminal. The fact that the electron is moving under the application of a force means that work is being performed on it and energy is being used up. The maximum amount of energy that can be used to push this electron from one terminal to the other is equal to the amount of potential energy the electron has prior to having this work done.

In other words, the electron has the potential to have work done on it by virtue of its location near the negative terminal, and the amount of potential work that can be done is called the potential energy.

In contrast, an electron very close to the positive terminal has very little potential energy because there is very little distance that the force can be applied over before the electron reaches the terminal.

Thank you!

Drakkith said:
he fact that the electron is moving under the application of a force means that work is being performed on it and energy is being used up. The maximum amount of energy that can be used to push this electron from one terminal to the other is equal to the amount of potential energy the electron has prior to having this work done.

is this pulling force known as the electromotive force? Also, is the energy possessed by the electron known as voltage? I thought potential difference is the amount of energy required to drive a coulomb of charge from a point to another.

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Lim Y K said:
is this pulling force known as the electromotive force?

nothing is being pulled

davenn said:
nothing is being pulled

is electromotive force = potential difference?

Drakkith said:
An electron at the negative terminal will feel a force that moves it towards the positive termina

is the force known as electromotive force?

Lim Y K said:
is electromotive force = potential difference?

quoting from elsewhere on the www

The electric charge that has been separated creates an electric potential difference that can be measured with a voltmeter between the terminals of the device. The magnitude of the emf for the battery (or other source) is the value of this 'open circuit' voltage
Dave

Lim Y K said:
is this pulling force known as the electromotive force? Also, is the energy possessed by the electron known as voltage? I thought potential difference is the amount of energy required to drive a coulomb of charge from a point to another.

The most accurate definition of EMF is too complicated to get into at this level, but for our purposes we can consider the EMF as the force that causes charges to move.

Electric potential difference (also known as voltage) is different from electric potential in that the former is equal to the work done, per unit of charge, in moving that charge between two points in an electric field. Electric potential is a measure of the potential energy a charged object has in an electric field and is equal to the work done in moving that object from infinity to its current position divided by the charge of the object.

In other words, voltage (electric potential difference) is the work done per charge in moving a charged object from point A to point B. Plain old electric potential is the work done per charge in moving a charged object from point A to infinity. When you move the charged object from point A to point B, the electric potential will change, and the difference between the electric potential at point A and at point B is, you guessed it, the electric potential difference.

It's a little confusing if you've never dealt with potential energy before.

Drakkith said:
The most accurate definition of EMF is too complicated to get into at this level, but for our purposes we can consider the EMF as the force that causes charges to move.

Electric potential difference (also known as voltage) is different from electric potential in that the former is equal to the work done, per unit of charge, in moving that charge between two points in an electric field. Electric potential is a measure of the potential energy a charged object has in an electric field and is equal to the work done in moving that object from infinity to its current position divided by the charge of the object.

In other words, voltage (electric potential difference) is the work done per charge in moving a charged object from point A to point B. Plain old electric potential is the work done per charge in moving a charged object from point A to infinity. When you move the charged object from point A to point B, the electric potential will change, and the difference between the electric potential at point A and at point B is, you guessed it, the electric potential difference.

It's a little confusing if you've never dealt with potential energy before.

The only that I'm struggling to understand is potential difference. So going by the equation V=E/Q , potential difference (volts) is the amount of work done (energy) by a coulomb of charge, right? Also, may i know how is potential difference a measure of the amount of potential energy that is converted to other forms of energy?

Lim Y K said:
The only that I'm struggling to understand is potential difference. So going by the equation V=E/Q , potential difference (volts) is the amount of work done (energy) by a coulomb of charge, right?

Without getting into the details, yes. If you spend X joules moving Y coulomb of charges between points A and B, then the voltage is equal to X/Y joules per coulomb.

May i know if ,for example, 9V passes through a light bulb in a circuit, will the light bulb use all 9V worth of energy or will it just use a certain amount and the remaining charges will flow to the negative terminal of the battery?

There are several sources of confusion resulting from misunderstood and loosely used words.
Potential energy is different form potential.
Potential energy (symbol U, unit Joule) is a general concept, seen in mechanics, as well as in electricity. In words, the force on a particle, whether it is a point mass in a gravitational field, or a point charge in an electric field, is in the direction of decreasing potential energy. It does not matter whether the charge is positive or negative. In both cases, the force on the charge is in the direction of decreasing potential energy. Certainly, it is true that absolute value of potential energy U is not defined, only differences in U are observed. But once the zero of U is defined at a particular point, it is defined everywhere.
Electric potential, or just potential (symbol V, unit Volt) is defined like this: At every point in space, there is a scalar quantity V, such that, if you place a point charge q (positive or negative) at that point, the potential energy is (q)(V). This is so whether the charge q is a positive or negative number. Similar to potential energy, absolute value of V is not defined, only differences in potential are observed.
If you take a 1.5 V battery, and you define the negative terminal to be 0V, the positive terminal is 1.5V. Now, if you place a +1C charge at the positive terminal, the potential energy is (+1C) (1.5V) = 1.5 J. If you place the positive charge at the negative terminal, the potential energy is (+1C) (0V) = 0J. If you place a - 1C charge at the positive terminal, the potential energy is (- 1 C) (1.5V) = - 1.5 J. If you place it at the negative terminal, the potential energy is (- 1 C) (0 V) = 0 J.
You can redefine the zero of potential, and can say, for example, that the positive terminal of the battery is at 0 V. Then automatically, the negative terminal is at - 1.5 V. The battery makes sure that it maintains the potential difference. The method of calculation of potential energy is the same, use U = qV, and recalculate all the values again.
In every case, you will notice that the positive 1C charge has a high potential energy at the positive terminal and low potential energy at the negative terminal. The negative charge has a high potential energy at the NEGATIVE terminal, and a low potential energy at the POSITIVE terminal.
Now use the rule that everything (mass, charge, does not matter) is pushed towards lower potential energy, and you will see that negative charges flow from the negative terminal of the battery, along the wire, towards the positive terminal, and positive charges flow from the positive terminal to the negative terminal

Drakkith
Lim Y K said:
May i know if ,for example, 9V passes through a light bulb in a circuit, will the light bulb use all 9V worth of energy or will it just use a certain amount and the remaining charges will flow to the negative terminal of the battery?
In this last post, there are two concepts wrong.
(1) Voltage does not pass through anything. A voltage difference exists (maintained by a battery) between the terminals or ends of a bulb. A CURRENT passes through the bulb.
(2) There is nothing called 9V worth of energy, since Voltage is not Energy. The energy (actually the power) used by the bulb is the current passing through it, multiplied by the voltage across it. For example, if 1 A of current is passing through the bulb, and 9V is the voltage across the bulb, then the power dissipated in (or used up by, if you prefer) the bulb is (1A) (9J) = 9 W. The symbol W stands for Watt, which is the unit of power.

## 1. What is electricity current and how does it flow?

Electricity current is the flow of electric charge through a conductor. It is caused by the movement of free electrons in a material. These electrons are pushed by an electric field, such as the voltage difference in a battery, and flow from the negative to the positive terminal.

## 2. What are the main components of an electrical circuit?

An electrical circuit typically includes a power source, such as a battery, wires to conduct the electricity, and a load, such as a light bulb or appliance. Other components may also be included, such as switches and resistors, depending on the specific circuit design and purpose.

## 3. What is the difference between AC and DC current?

AC (alternating current) and DC (direct current) are two types of electricity current. AC current changes direction periodically, while DC current flows in one direction continuously. AC is typically used for long-distance power transmission, while DC is commonly used in smaller devices and electronics.

## 4. How does resistance affect an electrical circuit?

Resistance is a measure of how difficult it is for electrons to flow through a material. In an electrical circuit, resistance can affect the amount of current that flows and the amount of voltage that is required to maintain that current. Higher resistance means lower current and higher voltage, while lower resistance means higher current and lower voltage.

## 5. What is the difference between an open and a closed circuit?

An open circuit is one that is not complete and does not allow electricity to flow. This can be caused by a break in the circuit or an open switch. A closed circuit is complete and allows electricity to flow through it. This allows devices to operate and receive power.

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