CURRENT, RESISTANCE AND

VOLTAGE

What is current?Current is the rate at which electrons flow past a point in a complete electrical circuit. At its most basic, current = flow.

An ampere (AM-pir), or amp, is the international unit used for measuring current.

Amps are named for French mathematician/physicist Andrè-Marie Ampére (1775-1836)

What is voltage?Voltage is the pressure from an electrical circuit’s power source that pushes charged electrons (current) through a conducting loop, enabling them to do work such as illuminating a light.

In brief, voltage = pressure, and it is measured in volts (V). The term recognizes Italian physicist Alessandro Volta (1745-1827), inventor of the voltaic pile—the forerunner of today’s household battery.

TYPES OF VOLTAGE1. Alternating current voltage

Commonly produced by utilities via generators, where mechanical energy—rotating motion powered by flowing water, steam, wind or heat—is converted to electrical energy

2. Direct current voltage■ Travels in a straight line, and in one

direction only.■ Commonly produced by sources of stored

energy such as batteries.■ Sources of dc voltage have positive and

negative terminals. Terminals establish polarity in a circuit, and polarity can be used to determine if a circuit is dc or ac.

■ Commonly used in battery-powered portable equipment (autos, flashlights, cameras).

What is resistance?

Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after Georg Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance. He is credited for formulating Ohm’s Law.

Resistance is a measure of the opposition to current flow in an electrical circuit.

DEGREE OF RESISTANCEConductors: Materials that offer very little resistance where electrons can move easily. Examples: silver, copper, gold and aluminum.

Insulators: Materials that present high resistance and restrict the flow of electrons. Examples: Rubber, paper, glass, wood and plastic.

ELECTRICAL CIRCUIT

NODES the electrical junction between two or more components

 CURRENT FLOWSCurrent flows from a high voltage to a lower voltage in a circuit. Some amount of current will flow through every path it can take to get to the point of lowest voltage (usually called ground).

SERIES CIRCUITS

• There’s only one way for the current to flow in the above circuit

• Series components all have equal currents running through them

PARALLEL CIRCUITS

• Components share two common nodes• Parallel components all have the same

voltage drop across them 

SERIES-PARALLEL CIRCUIT

Circuit is neither simple series nor simple parallel. Rather, it contains elements of both

Basic Ohm's LawOhm’s Law is a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.To students of electronics, Ohm’s Law (E = IR) E = I x R

When spelled out, it means voltage = current x resistance, or volts = amps x ohms, or V = A x Ω.

To find the Voltage, ( V )[ V = I x R ]      V (volts) = I (amps) x R (Ω)

To find the Current, ( I )[ I = V ÷ R ]      I (amps) = V (volts) ÷ R (Ω)To find the Resistance, ( R )[ R = V ÷ I ]      R (Ω) = V (volts) ÷ I (amps)

Example 1: Voltage (E) and resistance (R) are known

Example 2: Voltage (E) and current (I) are known

Example 3: Current (I) and resistance (R) are known. What is the voltage?

1. If the circuit has a current of 2 amperes, and a resistance of 1 ohm, what is the voltage?

RESISTOR COLOR CODING• The first and second

band represent the numerical value of the resistor,

• The color of the third band specify the power-of-ten multiplier.

If the band is gold, it specifies a 5% tolerance; silver specifies a 10% tolerance; if no band is present, the tolerance is 20%.

■The colors brown, red, green, blue, and violet are used as tolerance codes on 5-band resistors only. All 5-band resistors use a colored tolerance band. The blank (20%) “band” is only used with the “4-band” code (3 colored bands + a blank “band”)

Tolerance•Tolerance is the precision of the resistor and it is given as a percentage. For example a 390 resistor with a tolerance of ±10% will have a value within 10% of 390, between 390 - 39 = 351 and 390 + 39 = 429 (39 is 10% of 390).•BROWN:   1%•RED:           2%•GOLD:        5%•SILVER:     10%•NOTHING:  20%

■THE END!!!