Electricity Flashcards
define current
rate of flow of charge per into time
define P.D
energy transfer per unit charge
what is ohms law
for any ohmic conductor current is directly proportional to p.d (given physical conditions remain constant)
what does the current voltage graph look like for an ohmic conductor
straight line though the origin
what is a semiconductor diode
only allows charge to flow in one direction
(one direction will high high resistance the other will have low)
when is ohms law obeyed in a filament lamp
at vey low current
- at high currents resistance is not constant therefore ohms law is not obeyed
when will resistivity be constant
at constant temperature
Explain how resistance increases in a metal proportionally to temperature
rise in thermal energy is transferred to kinetic energy of atoms causing them to vibrate this cause more collisions between free electron and metal atoms therefore reducing current flow
what happens to the resistance of a thermistor when temperature increases
resistance decreases
why does a thermistors resistance temperature relationship exist
as temperature increases the number of electron emitted from the atoms in the thermistor increases meaning there is greater current and therefore resistance decreases
what is an application of a thermistor
Heating in a household
what is a superconductor
When a material is below a certain temperature it will have 0 resistivity
2 applications of superconductors
Power cables
strong magnetic fields
what is power
energy transferred per unit time
what are the current voltage characteristics of a series circuit
Current is the same
voltage is shared across components in ratio of resistances
what is the current voltage characteristics of a parallel circuit
current is shared across all branches in ratio of resistance
voltage is the same across each component
what is the total voltage when joining batteries in series
sum of all the voltages
- what is the total voltage when joining equal battery’s in parallel
- why is this ?
- the voltage is equal to the voltage of one
- current is split equally between battery’s therefore overall potential difference of arrangement is as if there is 1 battery
what is Kirchhoff’s first law
- what does it show?
current into a junction = current out of the junction
- it shows charge is conserved
what is Kirchhoff’s second law
what does this show
- the sum of all voltages in a circlet = the battery voltage
- shows energy is conserved
what is a potential divider
Resistors connected in series across a voltage source used to divide p.d
how can you make a variable potential divider
add a variable resistor
what causes internal resistance
electrons colliding with atoms in the battery therefore some energy is transferred from electrons
what is the electromotive force
Total work done by a cell per coulomb of charge
