1. CURRENT,
RESISTANCE
AND VOLTAGE

2. 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.

3. 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)

4. 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.

5. 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.

6. TYPES OF VOLTAGE
1. 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

7. 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).

8. 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.

9. DEGREE OF RESISTANCE
Conductors: 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.

10. ELECTRIC
AL
CIRCUIT

11. NODES
the electrical junction between
two or more components
CURRENT FLOWS
Current 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).

12. 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

13. PARALLEL CIRCUITS
• Components share two common nodes
• Parallel components all have the same voltage drop
across them

14. SERIES-
PARALLEL
CIRCUITCircuit is neither simple series
nor simple parallel. Rather, it
contains elements of both

15. Basic Ohm's Law
Ohm’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, orV =
A x Ω.

16. To find theVoltage, (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)

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

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

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

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

24. 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%.

25. ■ 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”)

27. 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%

30. ■THE END!!!