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Electrons waves and photons (Energy, power, and resistance (Emf and pd…
Electrons waves and photons
Charge and current
Charge
Current is rate of flow of charge
Charge is measured in coulombs
An electron has charge -e and a proton has +e
Current is the movement of electrons or ions
Conventional current flows positive to negative, whereas electons flow negative to positive
Kirchoff's first law states the currents enering a junction = the currents leaving the junction
Mean drift velocity
I = Anev
Conductions have a high n, insulators have a low n
n is number density of charge carriers
Energy, power, and resistance
Emf and pd
Both measured in volts
1 volt is 1 joule per coulomb
Pd is the energy transferred from electrical energy to other forms
Emf is the energy transferred to electrical from other forms
W = VQ
Resistance
The ratio of pd to current
Measured in ohms
1 ohm is 1 volt per amp
Ohm's law states that current is proportional to voltage when temperature is constant
Resistivity