Topic 4.2: Energy, Power, and Resistance Flashcards
what is potential difference ?
the work done per unit charge measured in volts
what is the difference between voltage and EMF ?
voltage is the energy transferred per coulomb across a load resistance
EMF is the total amount of work done by the battery per coulomb
what is resistance ?
how difficult it is for current to flow through an appliance
the pd required for each unit of current that flows through a resistor
what is the definition of 1 Ohm ?
when a resistor is subject to a voltage 1V and allows a current of 1A through , its resistance is 1 Ohm
what is an ohmic conductor ?
A conductor that obeys Ohms Law
what is Ohms Law ?
the current through an ohmic conductor is directly proportional to the potential difference across it.
this is only true if the temperature is constant
why does the current increasing on a filament lamp cause an increase in resistance ?
the flow of current causes collisions between the electrons and the metal lattice
these collisions increase the temperature of the lattice
as the temperature increases , more collisions occur , causing resistance to increase
what is a diode ?
a diode is a appliance that only allows current to flow in one direction
what is a light dependent resistor (LDR)
a semiconductor that is sensitive to light : as the light intensity increases the resistance decreases
How does a thermistor work ?
as the temperature increases , the resistance decreases
resistivity
is a property of a metal which shows how easy or difficult it is for current to flow in the material (at a specific temperature)
describe an experiment to determine the resistivity of a metal
measure the diameter of your wire using a micrometre
use this to calculate the area
set up the circuit
vary the length and record the voltage and current for each length
use R=V/I to work out resistance
the gradient = resistivity / area
rearrange to work out resistivity
what is power ?
the rate of energy transfer
measured in joules/second or watts
