1.4-5 Measurement of Current and the Ammeter

Today we finish the first module of the Navy Basic Electricity and Electronics course from the early 70s. The module has been on Electrical Current. Previous review posts have included:

1.1 Electricity and the Electron
1.2 Electron Movement
1.3 Current Flow

We finish today with sections 4 and 5.

Here are the bullet points to remember from section 4:

• When you add more battery cells in a series, a light bulb burns with greater intensity. More "current" is flowing through the bulb.
• When we measure current, we are in effect measuring the (net) amount of electrons going past a given point at any given time.
• A "coulomb" of electrons is 6,250,000,000,000,000,000 electrons (6.25 x 10¹⁸). Discussing electrons in groups this large makes it easier for us to talk about them.
• The measure of current is called an amp (for ampere). 1 amp of current is one coulomb passing any point in a circuit per second. 1 amp = 1 coulomb per second.
• I is the abbreviation for current or number of amps. a is the abbreviation for amps. The symbol for charge or coulombs is Q. So I = Q/T.
• This section also introduces scientific notation. Especially important are micro (10^-6) and milli (10^-3).

Section 5 is then relatively brief by comparison. It deals with the tool used to measure current.

• An ammeter is used to measure current.
• An ammeter needs to be connected in "series," which means that all the current has to run through it.
• the positive lead of the ammeter should connect to the positive side of the circuit and the negative lead to the negative side. In other words, "observe polarity."
• De-energize the circuit before connecting the ammeter. Then re-energize. Also de-energize before disconnecting.

Next week: 2.1 Electromotive Force