Resistance
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21 Terms
Resistance definition
Opposition to the flow of electric current
Resistance symbol
R
Resistance unit
Ohms (Ω)
Current symbol
I
Voltage symbol
V
Formula
Resistance = voltage ÷ current
Symbol equation
R = V ÷ I
Rearranged for voltage
V = I × R
Rearranged for current
I = V ÷ R
Meaning of high resistance
Harder for current to flow
Meaning of low resistance
Easier for current to flow
Factors affecting resistance
Length, thickness, material, temperature
Longer wire
Higher resistance
Thicker wire
Lower resistance
Material effect
Metals like copper have low resistance; nichrome has high resistance
Temperature effect
Higher temperature increases resistance in metals
Ohmic conductor
Current is proportional to voltage (constant resistance)
Non‑ohmic conductor
Resistance changes with voltage or temperature
Ohmic graph shape
Straight line through origin (V–I graph)
Non‑ohmic graph shape
Curved line (e.g., filament lamp)
Key idea
Resistance determines how much current flows for a given voltage
