Let’s Get Physics-l: Charge and Electric Current

In terms of electricity, Charge and Electric Current are pretty important. Charge itself is a property which, surprise surprise, charged particles have.  It comes in two forms which are positive and negative charge and it is measured in Coulombs/ C (After Charles-Augustin de Coulomb, un physicien (A bit of French for a French physicist)).

Atoms are a great example of charged particles at work. They are composed of neutrons, protons and electrons but themselves have no charge. This is because the number of electrons is equal to the number of protons so their positive and negative charges are “cancelled” out, as it were. It’s sort of like having two armies of equal size and ability fighting against each other, neither side gaining the advantage. They are evenly matched so balance each other out in a similar way the positive charge of protons balances out the negative charge of electrons.

At the very core of charge we have something called the elementary charge which is the charge of electrons and protons. The elementary charge, or e for short, has a value of 1.6 x 10^-19 C (^ meaning to the power of) which is ridiculously small. This elementary charge can help us to calculate the number of electrons present in a charged particle as all charges are, in effect, a multiple of e. To differentiate between the elementary charges of protons and electrons we say protons have a charge of + 1.6 x 10^-19 whilst electrons have a charge of – 1.6 x 10^-19.

Now, Electric current and charge are very much connected (Though that shouldn’t really come as a shock (I’m not even sorry) to anyone) as current is the rate of flow of charge (carriers) in a circuit. Or, in other words (A very loose use of the word):

I= ∆Q/∆T

  • I – Current (A)
  • ∆Q – Change in Charge (C)
  • ∆T – Change in time (s)

This, in effect, shows that Current is equal to charge per second (Cs^-1) which is the rate of flow of said charge.

I added carriers in the definition namely because the charge itself is “carried” around a circuit by charged particles (NOTE: You don’t have to include carriers and charge on its own is more than acceptable in the exam). In a circuit, the delocalised (free, random moving) electrons are the charge carriers which drift (Important word, remember this for a future post (You don’t actually have to as I probably won’t)) slowly through the wire when current is passed through the circuit. In electrolytes (Fancy water which has ionic (Charged atoms which have lost or gained electrons one way or another) compounds dissolved within it) the charge carriers are the ions found in the dissolved compound.


  • Charge – property that certain particles have that comes in two forms, positive and negative charge. Measured in Coulombs (C)
    • Atoms – neutral charge because positive protons and negative electrons are equal in quantity.
    • Ions – charged particles with fewer/more electrons than protons, caused via ionisation
    • Elementary Charge – e – charge of subatomic particles protons and electrons which is equal to 1.6 x 10^-19 C
  • Current – Rate of flow of charge around a circuit. Measured in Amps (A)
  • I= ∆Q/∆T
    • I – Current (A)
    • ∆Q – Change in Charge (C)
    • ∆T – Change in time (s)

That’s Charge and Electric Current! I intend to post a few more physics posts in the next few hours in the wake of a looming Physics test so if anyone has any requests I will happily attempt to oblige with a reasonable explanation of whatever topics are requested (That is more aimed at fellow A-level Physics students but anyone is welcome to put forward a suggestion (Preferably electricity or Forces and motion related please)). If there aren’t any suggestions I will continue as I have personally planned to do so. As ever, if you have feedback, thoughts or questions be my guest and leave in them in the comments.




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