Current electricity

Current

• Electrical current is a flow of charge, it flows from positive to negative.

• Electrons flow from negative to positive.

• The longer side of the battery symbol is positive.

• Q=I*t

  • Q= Charge [C] coulombs

  • I= Current [A] amps

  • t= time [s]

• Current in series is the same everywhere.

• Current in parallel splits and recombines at junctions (not necessarily equally).

Potential Difference — Voltage

• Voltage is the amount of energy per Coulombs (energy each unit of charge has).

• E=V*Q

  • E= Energy [J] joules

  • V= Voltage [V] volts

  • Q= Charge [C] coulombs

• Voltage splits across all components in series.

• Voltage is the same across all branches in parallel.

Resistance

• How difficult is it for current to flow.

• Good conductors have very little resistance.

• Ohms law:

• V=R*I

  • V= Voltage [V] volts

  • R= Resistance[Ω] ohms

  • I= Current [A] amps

• Everything follows Ohms law.

• But when a component “obeys the Ohm’s law” resistance is constant.

• Light bulb

  • When the current increases the temperature increases.

  • As the temperature increases the particles in the filament gain KE and vibrate more.

  • This makes it hard for current to flow, so resistance increases

• For a filament lamp, we also draw the negative (current flows the other way)

• But a light bulb is not affects by current direction, so it looks the same, just with negative values

• Light bulb does not obey the Ohm’s law

LDR — Light dependent resistor

• As light intensity increases, resistance decreases

Thermistor

• As the temperature increases, resistance decreases (opposite to light bulbs/wires)

Diode

• Only allows current to flow in one direction

• Protects microchips from current in the wrong direction

Wires

• As the length increases, the resistance increases. It is linear