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electric charge and current of electricity - Coggle Diagram
electric charge and current of electricity
charges
property of matter
2 types: POSITIVE and NEGATIVE
SI unit:Coulomb (C)
law of electrostatics : like charges repel unlike attract
an object with equal amounts of positive and negative charges in electrically nuetral.
electric current
current is the rate of flow of charge
I\=tQ
II \= current (A), QQ \= charge (C), tt \= time (s)
SI unit: Ampere (A)
two conventions
Conventional current: flows from positive to negative terminal (historical assumption).
Electron current: flows from negative to positive terminal (the actual movement of electrons).
conditions
There must be a potential difference between the two terminals.
There must be an unbroken, conducting path from high to low potential.
EMF and Potential difference
emf
Work done to drive a unit charge around the entire circuit.
Refers to pd across the terminals of the power source.
SI unit: Volt (V)
ε
=
W
Q
ε=
Q
W
potential difference (pd)
Work done to drive a unit charge across two points in the circuit.
SI unit: Volt (V)
V\=WQV\=QW
resistance and type of conductors
Resistance is the ratio of pd across a conductor to the current through it.
R\=VIR\=IV
SI unit: Ohm (Ω)
Factors affecting resistance: R\=ρLAR\=AρL
ρρ \= resistivity of material, LL \= length, AA \= cross-sectional area.
Longer wire → higher resistance; thicker wire → lower resistance.
ohmic conductors
Current is directly proportional to pd (V∝IV∝I).
Resistance remains constant regardless of current.
Example: metal wire at constant tempera
non-ohmic conductors
V and II are not directly proportional.
Resistance changes with temperature.
Examples: tungsten filament lamp, diode, thermistor.