Paper 2 Flashcards
(58 cards)
what are the four ways energy can be transferred
mechanically - forces like motors, friction, cars or by a force doing work
electrically - by moving charge doing work
by heating - burning, transferring a heat source
radiation - light and heat and sound
discuss energy being transferred by heating with a pan on a gas stove
when the system is the pan of water energy is transferred into the system by heating to the thermal energy stores of the pan and the water which increases their temperature
when the system is the camping stove and the pan, the energy is transferred from the chemical energy store of the gas to the thermal energy stores of the pan and water increasing their temperature
discuss energy being transferred by forces doing work in relation to a box being lifted and dropped
lifted:
as the box is lifted work is done against gravity which causes energy to be transferred to the box’s kinetic and gravitational potential energy stores.
dropped:
the gravitational force would do work to transfer energy from the box’s GPE store to its kinetic energy store
what happens when a force moves an object through a distance
work is done on the object and energy is transferred mechanically from one store to another
what is the equation for work done
force x distance moved in the direction of the force
what does a force doing work often cause
a rise in temperature as energy is dissipated to the thermal energy stores of the moving object and its surroundings. This means the process becomes wasteful and the efficiency of the process is reduced
efficiency equation
useful over total
what happens when you push something along a rough surface
you are doing work against frictional forces and energy is being transferred to the kinetic energy store of the object because it starts moving but some is also being transferred to thermal energy stores due to friction. This causes the overall temperature of the object to increase
what is power
the rate of energy transfer in watts
calculate power
energy over time
a motor does 4.8kj of work in 2 minutes find its power output
4.8kj = 4800j
2 minutes = 120 seconds
4800/120 = 40 watts
what happens when certain insulating materials are rubber together
negatively charged electrons will be scraped off one and dumped on the other
as the materials are insulators these electrons are not free to move and create a build up of charge called static electricity
the materials become electrically charged with a positive static charge on the one that has lost electrons and an equal negative static charge on the other
which way the electrons are transferred depends on the materials involved but it is always the negative electrons that move
what charge does acetate and polyethene go
acetate - positive
polyethene - negative
electrically charge objects…
exert a force on one another
how can we investigate like and opposite charges
suspend a rod with a known charge from a piece of string and placing an object with the same charge nearby will repel the rod and cause it to move away from the object. an oppositely charges object will attract the rod and move towards it
what happens when you rub a balloon on a wall
when you rub it on your hair it transfers electrons to the balloon leaving it with a negative charge and if you then hold the balloon against a wall it will stick even though the wall isn’t charged. That’s because the charges on the surface of the wall can move a little - the negative charges on the balloon repel the negative charges on the surface of the wall
this leaves a positive charge on the surface which attracts the negatively charged balloon
this is called attraction by induction
what happens if you run a comb through your hair and hold it near little bits of paper
electrons will be transferred to the comb making it negatively charged meaning when you hold it near the uncharged paper it causes induction to the paper which means they jump up and stick to the comb
why does too much static cause charge
as electric charge builds up on an object the potential difference between the object and the Earth which is at 0V increases
if the pd gets large enough, electrons can jump across the gap between the charged object and the earth - this is the spark
they can also jump to any earthed conductor that is nearby which is why you can get static shocks from clothes or getting out of a car
how do photocopiers use static electricity
to copy images onto a charged plate before printing them
how static electricity used in electrostatic sprayers
insecticide sprayers and paint sprayers to get a fine even coat of spray
- the spray gun is charged which charges up the small drops of paint and each paint drop repels all the others since they’ve all got the same charge creating a fine even spray
- the object to be painted is given an opposite charge to the gun which attracts the fine spray of paint
- this method gives an even coat and hardly any paint is wasted in addition parts of the bicycle or car pointing away from the spray gun still receive paint so there are no paint shadows
insecticide sprayers work the same but the crops to be sprayed are charged by induction as the droplets come near them instead of being given an opposite charge
what are the dangers of static electricity
refuelling cars - as fuel flows out of a filler pipe into an aircraft or tanker then static can build up which can lead to a spark and explosions in dusty or fumy places
static on airplanes - as planes fly through the air friction between the air and the plane causes the plane to become charged and this build up of static charge can interfere with communication equipment
lightning - raindrops and ice bump together inside storm clouds leaving the top of the cloud positively charged and the bottom of the charge negative. This creates a huge voltage and a big spark which can damage homes or start fires when it strikes the ground
earthing
provides an easy route for the static charges to travel into the ground. this means no charge build up to give you a shock or spark
the electron flow down the conductor to the ground if the charge is negative and flow up from the ground if the charge is positive
how can sparking be explained by electric fields
when an object becomes statically charged it creates its own electric field
interactions between this field and another field and other objects are the cause of events like sparking
for example the comb becomes charged and so produces an electric field. the electric filed interacts with the pieces of paper and so they feel a force
this force causes them to move and stick to the comb
sparks are caused when there is a high enough pd between a charged object and the earthed object. The strong electric field causes electrons in the air
particles to be removed known as ionisation
air is normally an insulator but when ionised it is much more conductive so a current can flow through it, this is the spark
what happens when a current-carrying conductor is put between a magnetic poles the two magnetic fields interact
the result is a force on the wire
