P4 Electric circuits Flashcards
what happens when you rub a polythene rod with a dry cloth
electrons are transferred to the surface atoms of the rod from the cloth so the polythene rod becomes negatively charged
what happens when you rub a perspex rod with a dry cloth
electrons are transferred from the rod to the surface atoms of the cloth so the rod becomes positively charged
which way does charge travel around a circuit
from + to -
what is the equation to work out charge (coulombs)
current (amps) x time (seconds)
what is the equation for potential difference
energy transferred (j) / charge (coulombs)
what is the equation for resistance (ohms)
potential difference (v) / current (amps)
what is ohm’s law
the current through a resisitor at constant temperature is directly proportional to the potential difference across the resistor
why is a wire called an ohmic conductor
its resistance stays constant as the current changes, provided the temperature is constant
what is an LDR and how does it work
light dependant resistor - resistance decreases if light intensity increases and vice versa
how does a thermistor work
resistance decreases if temperature increases and vice versa
what is the current rule in a series circuit
the same current passes through each component
what is the potential difference rule in a series circuit
the potential difference of the power supply is shared between the components
why does adding more resistors in series increase the total resistance
the current through the resistors is reduced and the total potential difference across them is unchanged
what is the current rule for parallel circuits
the total current through the whole circuit is the sum of the currents through the separate branches
what is the potential difference rule for parallel circuits
the potential difference across each component is the same
