Konsep Arus dan Tegangan

Basic concept of CURRENT and VOLTAGE2nd and 3rd class meeting.Sigit Tri Wicaksono, Ph.D.Did you ever been got electric shock ???, how do you feel ???

Electrical currentCurrent is a measure of.Current is measured using An ammeter is always placed in series in a circuit

Quantitatively, current is the net rate of charge crossing an area. Its units are coulombs per second, which is given the name ampere (A) after the French physicist Andr Marie Ampre (17751836). In electronics and biomedical applications, currents are small enough that milliamperes (mA) and microamperes are widely used. When current I is steady or a time average will do, we write

Aktor dibalik arus listrikElektronProtonIon

Example

Current and Current Density: Through the Cell MembraneIon channels are narrow pores that allow ions to pass through cell membranes. A particular channel has a circular cross section 0.15 nm in radius; it opens for 1 ms and passes 1.1 x 104 singly ionized potassium ions. Find both the current and the current density in the channel.Current is the rate of charge passing through a given area, here the opening of an ion channel. Equation 24.1a, determines the current. Current density, however, is current per unit area, which we can compute from J= I/A

Current Conduction Mechanism

1. Conductor Ohms Law

2. Ionic solutions Liquid solutions contain positive and negative ions that respond to an electric field by moving in opposite directions, resulting in a net current. Conductivity is limited by collisions between ions and neutral atoms and, as Table 24.1 suggests, ionic solutions are poorer conductors than metals. Ionic conduction is essential to life, as the transport of ions through cell membranes in Example 24.2 suggests. Electric eels use ionic conduction to sense and kill their prey. Batteries and fuel cells use ionic conduction, which also plays a role in the corrosion of metals. And an ionic solutionsweatincreases our vulnerability to electric shock.

Plasma is ionized gas that conducts because it contains free electrons and ions. It takes substantial energy to ionize atoms, so plasmas usually exist only at high temperatures. Plasmas are rare on Earth; theyre in fluorescent lamps, plasma TVs, neon signs, the ionosphere, flames, and lightning flashes. Yet much of the universes ordinary matter is in the plasma state; stars, in particular, are mostly plasma.The electric properties of plasma make it so different from ordinary gas that plasma is often called the fourth state of matter. Some plasmaslike the Suns coronaare so diffuse and therefore collisions so rare as to make them far better conductors than metals.These collisionless plasmas can sustain large currents with minimal electric fields.3. PlasmaEven in insulators, random thermal motions dislodge a few electrons, giving these materials very modest conductivity. In a few materialsnotably the element siliconthis effectis significant at room temperature. Such materials have conductivities between those of good insulators and metals, so theyre called semiconductors.4. Semi ConductorIn 1911 the Dutch physicist H. Kamerlingh Onnes found that the resistivity of mercury dropped to zero at a temperature of 4.2 K. Today we know thousands of substances that become superconductors at sufficiently low temperatures5. Super Conductor

Voltage / potential difference Voltage is a measure of the energy carried by the current.(Technically it is a measure of the difference in energy between two points hence the name potential difference).

Keep in mind:A car has a 12-V battery, means the battery does 12 Joules of work on every coulomb of charge that moves between its terminalsVoltage / potential differenceVoltage is measured with a voltmeter.Voltmeters are always placed in parallel in a circuit.

AC and DC current/voltageAC current/voltage is frequency dependent, Indonesia has 220V, 50-60Hz AC source, what it does mean??

What about DC voltage???A way to provide high efficiency, safe low voltage:

High Voltage Transmission LinesLow Voltage to Consumersstep-up to 500,000 Vstep-down,back to 5,000 Vstep-down to 220 V~5,000 VoltsCorrelation between I and VOHMS LAWV = R . i (remember, F = m.a)

KIRCHOFFS LAWKCL

KVL

DISSIPASION ENERGY (Ohmic losses)Current flow within a conductor (close circuit) always produce HEAT, Explain !!!??CASE STUDY... Discuss the applications of basic concept of current and voltage !!!