Electricity Flashcards
What is an ohmic conductor?
A conductor that obeys ohms law (resistor at constant temperature)
Describe the reason for the shape of the current-voltage graph of filament lamps
As the current increases the filament heats up meaning the resistance increases. This is because the energy transfer increases the lattice vibrations, leading to more frequent collisions between the e- and lattice ions
When does current rapidly increase in a diode?
Around 0.7v because this is when the resistance rapidly decreases
What direction is conventional current?
Positive to negative (but the electrons actually move from negative to positive)
What causes resistance?
Collisions between the charge carriers in the material with each other and the fixed positive ions in the material in which the current is flowing
What are the rules for thermistors and LDR’s?
T.I.R.D
Temperature Increases Resistance Drops
B.I.R.D
Brightness (intensity) Increases Resistance Drops
Define current
The rate of flow of charge
Define potential difference
The work done in moving in a unit charge between two points
Define resistance
The ratio of the potential difference applied across a component to the current passing through it
What does resistivity depend on?
Material structure
Environmental factors (light, temperature)
Define emf
The energy transferred by a power source to each coulomb of charge
What is kirchoff’s first law
Conservation of charge, at any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction
What is kirchoff’s second law
Conservation of energy. The sum of the potential differences around a circuit is equal to the sum of the emfs of the power source
What is a potential divider?
A pair of resistors that divide input pd in the ratio of the resistors
What is the equation for a potential divider?
V(out)/v(in)=R1/R1+R2
