# Supplementary Note 1A Resistor

```Supplementary Note 1A
Basic Electronic Component: Resistor
Resistor
• A device to limit current in a circuit.
• Unit: Ohm ()
• Ohm’s Law: 1  = 1V/1A
1A
1V
1
V-I Relationship
• Recall Ohm’s Law
𝑉𝑅 = 𝐼𝑅 𝑅
V/V
Slope = V/I = R
I
V
I/A
Assuming V is fixed,
The current 𝐼 is unchanged.
Power Dissipation
• When current goes through a resistor, power
dissipates at the resistor in a form of heat.
• Calculation of Power
𝑉𝑅2
𝑃 = 𝑉𝑅 𝐼𝑅 =
= 𝐼𝑅2 𝑅
𝑅
The unit of Power is Watt (W)
Types of Resistors
• Wirewound
Higher power rating
• Film (metal / metal oxide/ carbon)
Types of Resistors (Cont’)
• Surface Mount Resistor (Chip Resistor)
– Very small
– Limited power rating: 1/8W – 1/4W
– Thin film / thick film process
Resistance Value
• Color code (usually for carbon/metal resistors)
Resistance Value
• 3-digit or 4 digit
(usually for surface
mounted resistor)
Available Resistors in Market
• Not all resistance values are available
• Use the closest (if design is allowed)
Tolerance
• Tolerance: All manufacturing processes have some
degree of variations, which affect the accurate of the
resistance.
• Tolerance: 20%, 10%, 5%, 2%, 1%, 0.5%, 0.25%, 0.1%,
0.05%, 0.02% differ from the nominal value
• Eg. A resistor with 10K and 10% tolerance, its value can
be from 9K to 1.1K
Variable Resistor (Potentiometer)
• The two ends are fixed
• No. of turns determines the precision of
VR, eg. 10 turns, 20 turns
```
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