Drift Velocity Equation & Formula

    Although you can solve for drift velocity using the drift velocity equation, using this drift velocity calculator is a lot easier. Use it to find the velocity of a given charged particle in a type of material. In this article, you will learn how to calculate drift velocity using the drift velocity formula, how to use the calculator, and more.

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    How to use the drift velocity calculator?

    Using this drift velocity formula is faster and more efficient than performing the calculation manually with the drift velocity equation, the drift velocity formula or the drift speed equation. This is an easy to use online tool that requires very few values. Here are the steps to take for this calculator:

    • First, enter the Current value and choose the unit of measurement from the drop-down menu.
    • Then enter the value of the Area and choose the unit of measurement from the drop-down menu.
    • Finally, enter the value of the Number Density and choose the unit of measurement from the drop-down menu.
    • After entering all of the required values, the online tool instantly generates for you the value of the Drift Velocity.

    How do you calculate drift velocity?

    The drift velocity refers to the average velocity what an electron, ion, electron hole or any other particle reaches in a given material when a voltage gets applied to it. If you want to determine the value of the drift velocity using the drift velocity equation, you should know the value of the number density.

    This tells you the number of carriers contained in a volume unit of a given material. It’s typically expressed in carriers per cubic meter. In order to calculate the drift velocity, you need the drift speed equation to perform simple calculations for an electron’s velocity.

    Electric currents refer to the movement of electrons and other electric charges in a wire. This may come as a surprise to a lot of people but the particles here possess a limited velocity. As soon as you connect an electrical device to a socket, this immediately starts a reaction.

    Therefore, how fast does electricity travel? To solve this, you need to perform the basic calculations of drift velocity. Although we can already assume that the current velocity is fairly small, there are a lot of electrons which feel the applied voltage all at the same time.

    This is why electronic devices react so quickly after you’ve connected them to a socket. You can use the drift velocity calculator for any kind of charged particle since this online tool also uses the following drift velocity equation:

    u = I / (n * A * q)

    where
    u refers to the drift velocity or the average velocity of a given particle
    I refers to the current which you can compute also using Ohm’s law if you don’t have the value yet

    n refers to the charge carrier number density
    A refers to the cross-sectional area of a wire
    q refers to the charge on the charge carrier

    This online calculator assumes that a given current appears as a result of an electron flow with an elementary charge of q = e = 1.6 * 10^(-19) C. In cases when you want to modify the type of charge carrier, you may do this in the advanced mode.

    What is drift velocity and its expression?

    In physics, the drift velocity refers to the average velocity reached by electrons and other kinds of charged particles in a given material because of an electric field. Generally, electrons in conductors tend to randomly propagate at the Fermi velocity. This results in a zero value for the average velocity.

    When you apply an electric field to the random motion which occurs in a small net flow in a single direction, this is the drift. The drift velocity has a proportional relationship to the current. In resistive types of materials, the drift velocity also has a proportional relationship to an external electric field’s magnitude.

    Therefore, you can explain Ohm’s law in terms of drift velocity as well. The most fundamental expression of this law is:

    u = μ E

    where
    u refers to the drift velocity
    μ refers to the material’s electron mobility
    E refers to the electric field

    When using the MKS system, the units of these quantities are m/s, m2/(V•s), and V/m.

    In terms of expression, consider the length of a conductor I as well as the cross section’s area A. Then allow the number of free radicals for each unit of volume to be n. When you apply a pd V, allow the electrons’ drift velocity to be v. Therefore:

    • The total number of free electrons in one piece of the conductor is:

    nAl = number of free electrons per unit volume * volume

    • The total charge caused by free electrons is:

    q = nAle

    • The time taken by the charge to traverse the conductor completely is:

    t =l/v

    • Therefore, the current that flows in the conductor is:

    I=q/t = nAle/(l/v) = nAev

    What is the SI unit of drift velocity?

    The SI unit of drift velocity is also known as the axial drift velocity. Generally, electrons randomly propagate at the Fermi velocity. Here:

    • u refers to the drift velocity
    • μ refers to the electron mobility of the given material where the units of measurement are m2/(V⋅s)
    • E refers to the electric field where the units of measurement are V/m

    How does drift velocity vary with area?

    The drift velocity doesn’t depend on the cross-sectional area or the length of a wire when you’re dealing with ordinary macroscopic wires. But when you have a wire that’s too short, then it might start to rely on the length of the wire. Normally, though, wires aren’t this short.

    The reason drift velocity doesn’t wart with the cross-sectional area of a wire is that the I/A ratio remains constant. This is also known as the current density with the equation J=I/A. Therefore, if you double the value of A, you also double the wire capacity, thus J remains constant.