Understanding Resistors

• Resistors are vital components in electronics, and it's important to know their role and how to interpret them.

Understanding Resistance

• Resistance is the opposition to current flow.
• Intrinsic resistance in wires and components is determined by the material, length, cross-sectional area (diameter), and temperature.
• Resistance is directly proportional to the length of the component, meaning as length increases, resistance increases.
• Resistance is inversely proportional to the square of the diameter, the thinner wire has greater resistance.
• Resistance is directly proportional to temperature, when temperature increase, resistance increases.

The Role of Resistors

• Resistors are added to circuits since wire resistance is typically insufficient.
• A resistor is a two-terminal passive component that regulates electrical current flow by resisting the flow of charges.
• When a circuit contains high resistive elements current is small.
• Resistors prevent short circuits by opposing current flow.

Types of Resistors

• The two main types are fixed and variable resistors.
• Fixed resistors come in variations like carbon composition, carbon film, metal film, and wirewound, each suited for different applications.
• Larger resistors can handle higher power values.
• The resistance of a fixed resistor cannot be changed.

Fixed Resistor Types:

• Carbon film resistors are used for general purposes and in high voltage circuits.
• Carbon composition resistors are tiny, withstand high energy pulses, and are used in surge protection, high power supplies, strobe lighting, and welding equipment.
• Metal film resistors (blue or green) are very sensitive and accurate and used in meters, remote controls, and radios.
• Wirewound resistors are large, powerful, used in high power circuits, and as fuses/circuit breakers in industrial applications, the value is labelled on the resistor.

Resistor Identification

• The letter "R" represents resistors in circuit diagrams.
• Fixed resistors often have color bands indicating their value.
• Resistors can have 3, 4, 5, or 6 color bands.

Colour Codes

• 3-Band Colour Codes: color bands represent significant digits and the multiplier, with the first two bands indicating the first and second significant digits, respectively, and the third band indicating the magnitude. The default tolerance is ±20%.
• 4-Band Colour Codes: represent two significant digits, the multiplier, and tolerance. The first and second bands are the significant digits, the third is the multiplier, and the fourth is the tolerance.
• 5-Band Colour Codes: represent three significant digits, the multiplier, and tolerance. Bands one, two, and three signify digits, band four indicates the magnitude, and band five is the tolerance
• 5-band resistors are more precise than 4-band resistors, and 4-band resistors have a smaller tolerance than 3-band resistors.

Solid-State Resistors

• Solid-state resistors use semiconductors (transistors, diodes, integrated circuits).
• They switch/isolate control and load circuits using electrical and optical semiconductor properties and have no moving parts.
  • Types: surface mount, thin film, and thick film resistors.
  • Solid-state resistors use numerical codes instead of color for resistance values.
  • They have higher output resistance, are shock/vibration resistant, and handle high current/voltage.

Variable Resistors

• Variable resistors do not have a fixed ohm rating and can supply varying ohmic values via a sliding contact mechanism.
  • Types: preset, cermat, trimpot, rotary potentiometer, sliding potentiometer, and rheostat.
  • Used for volume/brightness control in devices like TVs, radios, and computer joysticks.

Ohmmeters

• An ohmmeter measures a resistor's resistance in Ohms (Ω).
• It verifies resistance or troubleshoots resistor-related connection issues.
• Connect the ohmmeter leads to the resistor terminals, the resistance displayed can be compared to the expected value.