physics ppe Flashcards
what are the seven main stores of energy
magnetic internal (thermal) chemical kinetic electrostatic elastic potential gravitational potential
what is magnetic energy
energy stored when repelling poles have been pushed closer together or when attracting poles further appart
what is internal (thermal) energy
total kinetic and potential energy of particles in an object
what is chemical energy
energy stored in chemical bonds
what is kinetic energy
energy of a moving object
what is electrostatic energy
energy when repelling charges moved closer and attracting charges further apart
what is elastic potential energy
energy stored when an object is stretched or squashed
what is gravitational potential energy
energy of an object at height
how long can energy remain in the same store
for millions of years or just a fraction of a second
when are energy transfers taking place
all the time
what happens when a system changes
change in the way some or all of energy is stored, can be transferred or dissipated
what are 4 examples of energy being transferred
mechanical work
electrical work
heating
radiation
what is the term for energy for being wasted
dissipation, spreads out into the surroundings
how is energy dissipated in a a mechanical system
when two surfaces rub together against friction
how to reduce dissipation in a mechanical system
use a lubricant
how to reduce dissipation in an electrical system
using energy-efficient components such as LED bulbs over filament lamps
how is energy usually lost
through heating up the surroundings
how can energy be sometimes dissipated
as sound waves
can energy be created or destroyed
no
what does energy come from and where is it transferred to
from one store to another
true or false: all the energy in the universe today was present at the Big Bang and will still be around until the end of time
true
how can a smartphone waste chemical energy
by converting it to internal energy through electrical work and releasing infrared radiation
what is the equation for kinetic energy
0.5 * mass * speed^2
what is the equation for elastic potential energy
0.5 * spring constant * extension^2
what is the equation for gravitational potential energy
mass * gravitational field strength * height
what is work done
energy transferred
what does the amount of work done depend on
the size of the force
the distance the force causes the body to move
what is the equation for work done
force * distance
what is the rate at which energy is transferred called
power
what is the equation for power (not electricity)
work done / time
what is the term for how good a device is at converting total energy to useful energy
effieciency
how are devices designed
to waste as little energy as possible
what is the equation for efficiency
useful energy transferred / total energy supplied
from where and to where can energy be transferred to or from
stores and place to place
how are the three ways energy moves
conduction
convection
radiation
how can conductivity of materials be compared
by examining the time taken to transmit energy through them
why is it better to have a window with two layers of glass and a layer of air trapped inbetween
because glass and air are both poor conductors as they have low thermal conductivities, the layer of air has the lowest and reduces the overall conductivity, they are also both transparent
materials needed for practical investigating methods of insulation
- thermometer
- stopwatch
- piece of card
- large beaker
- small beaker
method for required practical investigating methods of insulation
- put small beaker in large beaker
- fill small beaker with hot water from kettle
- put cardboard over beakers has lid, should have a hole
- put thermometer through hole
- record temperature in small beaker and start stop watch
- record water temperature every 2 minutes
- repeats steps with different insulating materials
- plot graph temp (y axis) time (x axis)
what does graph show from practical investigating methods of insulation
- shallowest curve is best insulator
- temperature falls quickly at high temps and slowly at low temps
- when beaker is heated, big difference between temp of beaker and temp of surrounding air, shows a high rate of transfer
- when beaker is cooler, low difference between temp and surrounding air, shows a low rate of transfer
hazards from practical investigating methods of insulation
- boiling water can scald skin, do not overfill the kettle
- knocking beaker off desk can scald skin, do experiment whilst standing
what happens when materials are heated
the molecules gain kinetic energy and start moving faster
what is temperature a measure of
average kinetic energy of the molecules
what does the amount of energy needed to heat an object depend on
- the mass of the material
- the substance of the material
- desired temperature change
what is the specific heat capacity of water
4,200 J/kg/degrees C
what is the equation for working out change in thermal energy
change in thermal energy = mass * specific heat capacity * temperature change
what are systems that can store large amounts of energy called
energy resources
what are the major energy resources that can produce electricity
- fossile fuels
- nuclear fuel
- bio-fuel
- wind
- hydroelectricity
- geothermal
- tidal
- water waves
- the Sun
4 places energy is needed in
- homes
- public services
- factories and farms
- transport
what are 2 dangers with fossile fuels
- release CO2 causing global warming
- release Sulphur Dioxide which causes acid rain
why does most of our electricity come from fossil fuels
- existing infrastructure cheaper than new alternatives
- high power output
advantage and disadvantage of nuclear fuel
-can release large amounts of energy compared to fossile fuels
-doesn’t emit CO2
but
-radioactive waste is difficult to store and dispose of
factors that influence governments’ decisions about the use of energy resources
political and economic pressures
what is a renewable energy resource
one that is being replenished as it is being used
how can renewable resources be replenished
- human action
- natural processes
what is a non-renewable energy resource
a resource with a finite amount and will eventually run out
why are fossil and nuclear power stations very reliable
- provide most of country’s electricity
- operate almost continuously
why is water power (tidal and hydroeletric) reliable and predictable
moon causes tides and rainfall fills reservoirs
why are many renewable resources unreliable
- cannot respond to increased demand
- sunny and windy weather cannot be guaranteed
- equipment used is expensive
function of a thermistor
at low temps, thermistor has high resistance
at high temps, thermistor has low resistance
function of a light-dependent resistor
low light levels, ldr has high resistance
at high light levels, ldr has low resistance
function of diodes
- allows current to flow one way only
- used to convert AC into DC
what is the difference between AC and DC
in dc electrons flow consistently in one direction around circuit
in ac, direction of electron flow contrinually reverses
what are electrons
negatively charged particles that transfer energy through wires as electricity
what is electrical current
flow of electrons
what is the equation for charge
current * time
what is the equation for potential difference
energy / charge
what is the equation for resistance
voltage / current
why does the resistance of a filament bulb increase with energy inputted
the higher temperature increase vibrations of ions which makes it harder for electrons to get past
how does electricity work in a series circuit
current is the same around the circuit
voltage splits but is added up
resistors connected in series are added up for total resistance
how does electricity work in a parallel circuit
current splits but is added up
voltage is the same around the circuit
total resistance is reduced as current can take multiple paths
what are the 2 equations for power electricity
current * potential difference
current^2 * resistance
where are the 3 wires in a plug and what are their colours
earth wire (green and yellow) top neutral wire (blue) left live wire (brown) right
function of outer insulation
all three wires bundled together and extra plastic insulation for safety
function of cable grip
holds the cable tightly so wires don’t become loose
function of live wire
carries the current
function of fuse
melts and breaks the circuit if the current gets too high
function of neutral wire
connects cable to wall and completes circuit
what would happen without an earth wire
live wire could touch the case and person who touches it could get electrocuted
how does earth wire prevent danger
connects to case and metal pipe underground, in event of danger the current will pass through to the ground instead
what is the equation for energy transferred
power * time
what do step-up and step-down transformers do
increase voltage and decrease current
decrease voltage and increase current
what is the function of a step-up transformer
to make sure that there is less heat is lost through the wire because of decreased current
how are cables ensured that the minimum amount of power is lost
- cables are thick so that their resistance is low
- high voltages reduece current through transmission lines
what are charged atoms called
ions
what happens when insulating materials rub each other
they become charged, the one that gains electrons becomes negative and the one that loses becomes positive
what happens when cloth is rubbed on a polythene rod
polythene gains electrons
duster loses electrons
what happens when cloth is rubbed on acetate
acetate loses electrons
duster gains electrons
why do insulators create static electricity
they prevent the elctrons from moving and the charge remains, conductors cannot hold charge as electrons move through them
what repels and attracts between positive and negative in an electrical field
positive charges move outwards
negative charges move inwards
why would someone rubbing their feet on a carpet become shocked when touching a door handle
you become negatively charged so when you touch the positively charged door handle, the extra electrons will want to transfer from you to the handle
why would an ammeter show a reading when a magnetic passes through a coil
the magnetic field around the magnet moves when the magnet does, the field lines cut through the coil which induces potential difference in the coil. A current is induced because the coil forms a complete circuit
different properties of matter between states of matter
soilid - particles tightly packed in regular structure
liquid - tightly packed but free to move
gas - particles spread out move randomly
what is the equation for density
mass / volume
do the solid and liquid of the same element have a similar density
yes because the particles are tightly packed
why would a gas have different density to the other two
because the same amount of mass is spread out in a wider area
how can the volume of an irregular shape be measured
using a displacement can
how does water displacement work
it is filled with water above a spout and is drained until water is level with bottom of spout, the volume of water in measuring cylinder is identical to the volume of object
