physics qma revision 2018 Flashcards
how to convert milliamps to amps
/ 1000
how to convert megavolts to volts
x1,000,000
function of ammeter
measures current
function of voltmeter
measures potential difference (voltage)
function of fixed resistor
allows a specific amount of current and voltage through
function of thermistor
as the temperature changes, the resistance changes
function of diode
only allows current to flow in one direction
function of light dependant resistor
as the light changes the resistance changes
what does resistance do
slows the flow of electrons in the circuit
what does high resistance mean
low current
low energy
higher potentail difference
what is ohms law
current is directly proportional to potential difference as long as the temperature is constant
what is a component that obeys ohms law called
an ohmic conductor
what is a series circuit
current is the same around the circuit
voltage splits but adds up what you put in
resistance gets added together
what is a parallel circuit
voltage is the same around the circuit
current splits but adds up what you put in
resistance is smaller than your lowest resistor
what happens as you increase the temperature on a thermistor
decrease the resistance
what happens as you increase the light on an ldr
descrease the resistance
how to calculate kinetic energy
0.5 x mass x speed^2
how to calculate gravitatinoal potential energy
mass x gravitational field strength x height
how to calculate power
energy transfered / time
work done / time
potential difference * current
current^2 x resistance
how to calculate efficiency
useful output energy transfer / total input energy transfer
useful power output / total power output
how to calculate charge flow
current * time
how to calculate potential difference
current * resistance
how to calculate energy transferred
power x time
charge flow x potential difference
method to calculate resistance for a filament bulb
- measure potential difference with a voltmeter
- calculate resistance using V / I
- independent variable (x axis) = potential difference
- dependent variable (y axis) = current
is a filament lamp an ohmic conductor
no
why isn’t a filament lamp an ohmic conductor
the graph curves because the electrons gain kinetic energy and collide with vibrating ions more frequently, causing resistance and thermal energy being given off
are fixed resistors ohmic conductors
yes
how does steepness on an IV graph correspond with resistance
the steeper the gradient, the higher the resistance
what is the independent variable in the length of the wire experiment
length of wire (x axst)
what is the dependent variable in the length of the wire experiment
resistance (y axis)
what is power measured in?
watts
what colour is the earth wire and what is its function
yellow and green, prevents shocks and fires, 0v unless there is a problem
what colour is the neutral wire and what is its function
blue, at or close to 0v
what colour is the live wire and what is its function
AC, alternates between high positive and high negative voltage (230v)
why are wires and pins made of metal
they have delocalised (sea of free electrons)
why are plug case and outer insulations made of plastic
they do not conduct electricity
what do transformers do
change the potential difference
what do step up transformers do and why
increase the potential difference and decrease the current so its more efficient (less thermal energy is wasted from resistance in wire)
what do step down transformers do and why
decrease the voltage and increase the current so the voltage is at 230V, safe for home levels
what is power
the rate at which work is done
what is work done
energy transferred
what is current
the rate of flow of electron (charge) around a circuit
what happens when two insulating materials are rubbed together
electrons only move, this means a material with more electrons than protons has a negative charge and the one with more protons has an equal but opposite positive charge
what happens when a rod is rubbed on a polythene cloth
the rod becomes negative because it gains more electrons, the cloth becomes positive and has an equal and opposite charge to the rod
what happens when a rod is rubbed on an acetate cloth
the rod becomes positive because it loses electrons so it has more protons than electrons, the cloth becomes negative and has an equal and opposite charge to the rod
what is a danger of static electricity
sparks causing fuel to ignite e.g. in cars and planes
how to earth a plane for refuelling
attach a metal cable, negative electrons will flow through. the charge will go from the plane to the ground and the charge will not build up instead it will be destroyed
in electrical fields which way do the arrows flow
from positive to negative
in electrical fields how can you increase the repulsion
by decreasing the distance
in a comb and moving belt model how is the belt charged and why
the belt is positively charged because the belt loses negative electrons to the dome
what happens when you touch the dome
your hair sticks up because of the negative charge
