**(Elektronika Dasar)**

__Electrical Current__The conductor - insulator demonstration illustrates two other important points:

- An immobile static charge flows through a conductor as an
**electrical current**. It then resumes its static state on the Electroscope foil leaves. - Electrical current flows from a region of high charge or
**potential**to a region of low potential.

**The Magnetic Connection**

A current flowing through a wire creates a

**magnetic field**around the wire. You cannot see the field, but you can observe its effect. Orient a compass so it needle points to the north (N) mark. Place a copper wire over and parallel to the needle. Then connect a flashlight cell across the wire and the needle will move away from its north-south orientation. (Leave the wire connected for only an instant to prevent the cell from overheating!)**Measuring Current Electricity**

The physical (or mechanical) motion of a magnetic compass needle in a magnetic field provides a convenient way to measure the quantity of current flowing in a wire. This is the basic of the

**moving coil current meter**used in the analog multimeter. To provide high sensitivity, the wire is warped as a coil.**Direct Current Electricity**

An electrical current can flow in either of two directions through a conductor. If it flow in only one direction, whether steadily or in pulses, it's called

**direct current (DC)**. It's important to be able to specify the quantity and power of a direct current. Here are the key terms:*Current (I)*

Current is the quantity of electrons passing a given point. The unit of current is the

**Ampere**. One ampere is 6,280,000,000,000,000,000 (6.28 x 10^18) electrons passing a point in one second.*Voltage (V or E)*

Voltage is electrical pressure or force. Voltage is sometimes referred to as

**potential**.**Voltage Drop**is the difference in voltage between the two ends of a conductor through which current is flowing. If we compare current to water flowing through a pipe, then voltage is the water pressure.*Power (P)*

The work performed by an electrical current is called power. The unit of power is the

**Watt**. The power of a direct current is its voltage timesits current.*Resistance (R)*

Conductor are not perfect. They resist to some degree the flow of current. The unit of resistance is the

**Ohm**. A potential difference of one volt will force a current of one ampere through a resistance of one ohm. The resistance of a conductor is its voltage drop divided by the current flowing through the conductor.

__Mr. Ohm's Law__Given any two of the above, you can find the other two using these formulas known as

**Ohm's Law**:V = I x R

I = V/R

R = V/I

P = V x I or I^2 x R

**Summing Up**: This is the "water analogy":

**Alternating Current Electricity**

A curent flowing through a conductor establishes a magnetic field around the conductor. This effect works both ways so that a current will flow in a field. You can easily demonstrate electromagnetic current generation with a coil of wire and a small magnet. Connect the leads of the coil to a meter designed to sense microampere. Insert a steel nail through the coil and stroke the magnet back and forth across the coil. The meter will indicate a few microampere each stroke.

When the magnet is stroked in one direction along the coil, electrons in the wire are moved in one direction and the

**direct current**is produced. On away from the coil, the direction of current flow is reversed. Therefore, if the magnet is stroked back and forth along the coil, a current which alternates in direction or polarity is produced. It's called an

**alternating current (AC)**. Alternating current is ussually produced by rotating a coil in a magnetic field.

**Sine Wave Measurement**

AC voltage is usually specified at a value equal to the DC voltage capable of doing the same work. For a sine wave this value is 0.707 times the peak voltage. It's called the

**RMS**(root-mean-square) voltage. The peak voltage (or current) is 1.41 times the RMS value. Household line voltage is specified according to its RMS value. Therefore, a household voltage of 120-volts corresponds to a peak voltage of 120 x 1.41 or 169.2-volts.

**Why AC is used?**AC is better suited than DC for transmission through long distance power lines. A wire carrying AC will induce a current in a nearby wire. This is the principle behind the

**Transformer**.

*to be continued..*Simple Basic Electronics (part 4)

Simple Basic Electronics (part 1) Simple Basic Electronics (part 2)

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