Electricity Flashcards
Force =
Mass*acceleration
Pressure =
Force/area
Work done =
Force*distance
Power =
Charge*voltage
Charge =
Current*time
Voltage =
Work done/charge
Resistance =
Voltage=current
Kirchhoffs first law
Sum of current into a junction is equal to current flowing out of it
Current definition
Rate of flow of charge
EMF definition (electromotive force)
Amount of energy transferred from chemical to electrical for every coulomb of charge
Coulomb definition
Charge that flows past a point in 1 second when the current is 1
P.d definition
Energy transferred to any other form of energy per unit charge
Charge*Voltage =
1/2mv^2
Charge of electron*Volatge =
1/2mv^2
1 volt =
The p.d between 2 points when 1 joule of work is done to move a charge of 1 coulomb
Power definition
Rate of transfer of energy
Resistance definition
Ratio of p.d to current across a component
Ohms law
For an ohmic conductor at a constant temp the current is directly proportional to the p.d
Percentage uncertainty =
Absolute uncertainty/measured value*100
Resistance =
(Resistivity*length)/area
When the temp increases…
The particles vibrate more which increases the resistance
Resistance in a filament lamp
-current flowing causes temp to increase
-temp increases causes the metallic lattice to vibrate more
-more vibrations mean more frequent collisions with electrons
-increases resistance
Resistance in a diode
-only conducts in one direction after threshold p.d is reached
-current increases by much greater proportion then p.d
-a protective resistor must be placed in the circuit to protect it as the diode has effectively no resistance
Resistance in a thermistor
-ohmic conductor so constant temp = constant resistance
-semiconductor so more free electrons released as temp increases so more charge can be carried
-this means resistance falls as temp increases
