Resistors Flashcards
Resistor
Definition:
A resistor is an electrical component that limits or regulates the flow of electrical current in a circuit. It is made of material that shows resistance to the motion of charges
Important Attributes:
Resistance Value: Measured in ohms (Ω).
Power Rating: The maximum amount of power it can dissipate, measured in watts (W).
Types: Can be fixed or variable.
Material: Typically made from carbon, metal, or metal oxide.
Examples:
Carbon composition resistor
Metal film resistor
Non-Examples:
Capacitor
Inductor
Fixed Resistor
Definition:
A fixed resistor has a resistance value that does not change.
Important Attributes:
Constant Resistance: Does not vary with voltage or current.
Stability: Provides stable resistance under varying conditions.
Common Use: Used in circuits where a specific
resistance is needed.
Examples:
Carbon film resistor
Metal oxide resistor
Non-Examples:
Variable resistor
Potentiometer
Variable Resistor
Definition:
A variable resistor is an electrical component whose resistance can be adjusted manually.
Important Attributes:
Adjustable Resistance: Resistance value can be changed.
Types: Includes potentiometers and rheostats.
Common Use: Used for tuning and calibration.
Examples:
Volume control knob (potentiometer)
Light dimmer switch (rheostat)
Non-Examples:
Fixed resistor
Diode
Rheostat
Definition:
A rheostat is a type of variable resistor used to control current by manually adjusting the resistance. AKA a current controlling device
Important Attributes:
Current Control: Primarily used to adjust current in a circuit.
Two Terminals: Typically has two terminals.
Construction: Often nichrome wire-wound for higher power ratings, around a ceramic core (Solenoid), and a sliding contact, aka wiper, that adjusts the resistance
Examples:
Light dimmer
Motor speed controller
Non-Examples:
Fixed resistor
Capacitor
Potentiometer
Definition:
A potentiometer is a three-terminal variable resistor that can be used to adjust voltage levels.
Important Attributes:
Voltage Divider: Often used to vary voltage in a circuit.
Three Terminals: One for the input voltage, one for the output voltage, and a third for the ground.
Applications: Used in audio equipment, sensors, and control devices.
Examples:
Volume control on a radio
Adjustable power supply
Non-Examples:
Fixed resistor
Inductor
How to calculate the resistance value of a resistor?
R = (p l)/A
R = resistance
p = specific resistivity of material
l = length of material
A = area of cross section of material
What happens when you exceed a resistor’s power rating?
If the power rating is exceeded for too long a period of time, the resistor will reach a point where it is no longer able to efficiently dissipate the heat and it will burn out.
What are carbon composite resistors made of?
A mixture of conductive carbon and insulating clay (ceramic).
What are carbon film resistors made of?
the consist of a ceramic core, which is coated in a thin layer of carbon. The resistance value is controlled by cutting a helical groove into the thin layer of carbon
What are metal film resistors made of?
A ceramic core coated with a thin layer of metal film, the resistance value is controlled by cutting a helical groove into the thin metal film layer
What are wire wound resistors made of?
Nichrome wire wrapped around a ceramic core. The resistance value is controlled by the amount of coils.
Where are wire-wound resistors most often used?
In high heat environments. The casing is often made form material that protects the core from external heat.
In situations where a high power rating is required. The casing of some wire-wound resistors can efficiently dissipate heat
What are SMD (surface mounted device) resistors made of?
A thin piece of resistive material on top of a ceramic base. The resistive value is controlled by cutting a groove into the resistive material to reduce it’s surface size
Pre-set resistor
Definition:
A preset resistor is a small adjustable resistor used to set precise values in a circuit, typically adjusted only once or infrequently.
Important Attributes:
Precision Adjustment: Used for fine-tuning circuit parameters.
Compact Size: Typically small and mounted on circuit boards.
Application: Used in calibration and trimming.
Examples:
Trimmer potentiometer
Adjustable resistor on a PCB
Non-Examples:
Standard potentiometer
Fixed resistor
Ohm’s law
Describes the relationship between voltage, current, and resistance
Ohm’s Law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them.
Formula: V= IR
