EOY exam Flashcards
what is the weight equation?
weight = mass x gravitational field strength (N) = (Kg) x (N/Kg)
what is the work done and power equation?
work done = force x direction
E = f x d
(J) = (N) x (m)
what is the power equation?
power = work done ÷ time taken
what is the potential difference equation?
V = I x R potential difference (volts) = current x resistance volts = amps x ohms
what is the pressure and pressure in a fluid equation?
pressure = force ÷ area
pressure (pascals)
pressure in a liquid = heigh/depth of column x density x gravitational field strength
P = h x ρ x g
pascals = m x kg/m3 x n/kg
what is the gravitational potential equation?
GPE = M x G x H
Gravitational potential energy = mass x gravitational field strength x height
(J) = (Kg) x (N/Kg) x (m)
what is the kinetic energy equation?
KE = 1/2 x mass x speed KE = 1/2 x m x v2 (J) = 1/2 x (m) x (m/s)
what is the specific heat capacity equation?
ΔQ = m x c x Δ ϴ
energy change = mass x specific heat capacity x temperature change
(J) = (Kg) x (J/Kg/degrees) x degrees
what is the specific latent heat equation?
Q = M x L
thermal energy = mass x specific latent heat
(J) = (Kg) x (J/Kg)
what is the charge equation?
Q = I x T charge = current x time
what is the force on a conductor equation?
F = B x I x L
force x magnetic flux density x current x length
what is specific latent heat and specific heat capacity?
SLH: the amount of energy required to change the state of 1Kg of substance
SHC: the amount of energy needed to raise the temperature of 1kg of substance by 1 degree
what is current ?
the flow of electrical charge around a circuit. Current will only flow through an electrical component if there is a potential difference across that component and if the circuit is complete.
what is potential difference?
(voltage) is the driving force that pushes charge around a circuit
the energy transferred per columb of charge that passes between two points
what is resistance?
anything that slows down the flow of charge
link potential difference, current and resistance?
the higher the potential difference across a given component, the higher the current will be
the greater the resistance of a component, the smaller the current flowing through it
what is the energy transferred equation?
energy transferred = charge moved x potential difference
E = Q x V
why does resistance increase with temperature?
when electrical charge flows through a component it has to do work against resistance causing an electrical transfer of energy.
Some of this energy is dissipated to the thermal energy stores of components and the surroundings so when a current flows through a resistor it heats up.
This happens because the electrons collide with the ions in the lattice that make up the resistor as they flow through it giving the ions energy to vibrate and heat up.
The more the ions vibrate, the harder it is for electrons to get through the resistor because there is more collisions. For a given pd the current decreases as the resistor heats up.
how can you reduce the amount of energy dissipated to thermal stores as the current flows between components
use low resistance wires
explain the energy transfers in a kettle?
electrically from the mains ac supply to the thermal energy store of heating inside the kettle
the higher the current…
the more energy is transferred to the thermal energy stores of the components
what are the negatives of heating in a circuit?
efficiency reduced because less energy is transferred to useful and more is transferred to it’s thermal energy stores
if temp gets too high the fuse can melt and break the circuit
what are the advantages to heating in a circuit?
toasters contain a coil of wire with a high resistance and when a current passes through it its temp increases and it glows red and gives off infrared radiation heating your bread
what does power transferred depend on?
pd and current
the pd tells you how much energy each unit of charge transfers
current tells you how much charge passes per unit of charge
how do you calculate power if you aren’t given the pd?
P = I SQUARED X R POWER = CURRENT SQUARED X RESISTANCE
what is static electricity?
the build up of electrons and charge as a result of friction
what charge does a polythene and acetate rod carry?
polyethene = - acetate = +
why will a balloon stick to a wall after you have rubbed it on your hair?
rubbing it on your hair transfers electrons to the balloon leaving it with a negative charge. Then it will stick to a wall because the charges of the surface of the wall can move a little so the negative charges on the balloon repel the negative charges on the surface of the wall leaving a positive charge on the surface of the wall therefore attracting the balloon via attraction by induction
what is static electricity in causing sparks
a build up of electric charge on an object means the potential difference between the object and the earth increases . If the pd gets large enough electrons can jump across the gap between the earthed object and the charged this is the spark
when object becomes statically charged it generates its own electric field and interactions between this field and other objects cause events like sparking
how can you stop electrostatic build up?
by earthing them providing an easy route for the static charges to travel to the safety of the ground
what happens when a charged object is placed in a electric field?
it feels a force caused by the electric fields around the two objects interacting
what happens between two oppositely charged parallel plates?
a uniform field is created with the strength and direction the same throughout except at the ends
what are magnetic materials?
iron
nickel
cobalt
steel
what is an induced or temporary magnet?
only produce a magnetic field while they’re in another magnetic field
this magnetic induction explains why the force between a magnet and a magnetic material is always attractive - the south pole of the magnet induces a north pole in the material and vice versa
What happens when you take away the magnetic field of an induced magnet and what does it depend on?
it will lose its magnetism but how quickly depend on…
magnetically soft materials like pure iron and nickel alloys lose it quickly
magnetically hard materials like steel lose it more slowly
what is Flemings left hand thumb rule?
thumb - direction of force (motion)
1st finger - direction of magnetic field
2nd finger - direction of current
how do you work out the size of force?
F = B x I x L force = magnetic flux density x current x length (N) = (T) x (A) x (m)
what is magnetic flux density measure in?
tesla (T) or N/Am
what is electromagnetic induction?
the induction of a pd and current if there is a complete circuit in a wire which is experiencing a change in magnetic field
how can you cause em induction
if a coil of wire (an electrical conductor) and a magnetic filed move close together
rotating a coil of wire in a magnetic filed cutting through the field lines
when the field size changes
how do you increase the size of an induced current ?
add more coils
add an iron core
move the magnet faster
increase field strength
what is the moments equation?
moment of force = force x distance
Nm) = (N) x (m
what is equal to m x SHC x Δθ
p x t
four different ways energy is transferred between stores?
mechanically
electrically
heating
radiation
ball rolling up a slope energy transfers?
does work against gravity
energy mechanically from KE store to GPE store
bat hitting a ball?
energy from bats KE store to balls KE store
some lost through heat and sound
rock dropped from cliff?
from gravity to KE assuming there is no air resistance
gravity does work on the rock so it accelerates
car slowing down without breaking
KE transferred mechanically due to friction and then by heating to the thermal energy stores of the car + road
a kettle boiling water ?
energy is transferred electrically from mains to the heating element and then by heating to the thermal energy store of the water
why do leavers make it easier to do work?
leavers transfer the turning effect of a force to make it easier to do work as they increase the distance from pivot
How do you calculate moment?
moment is the turning effect of a force
moment = force x distance from pivot
what is density and the equation?
density is the relationship between mass and volume
density = mass / volume g/cm3 = g / cm3
what are the state changes
solid -> gas = sublimation gas -> solid = deposition liquid -> gas = evaporation gas -> liquid = condensing solid -> liquid = melting liquid -> solid = freezing
what is fluid pressure?
fluid pressure if the pressure caused by the collisions of gas or liquid particles on a given surface.
fluid pressure increases with depth because there are more particles above
what happens when an object is submerged in a fluid?
the pressure of the fluid exerts a force on it in every direction
pressure increases with depth so the force exerted on the bottom of the object is larger than the force acting on the top of the object
this causes a resultant force called upthrust which is equal to the weight of the fluid that has been displaced by the object
when does an object float?
if the upthrust is equal to the objects weight the forces balance out
wether or not an object floats depends on its density
less dense then fluid it floats
why does atmospheric pressure decrease with height ?
as the altitude increases the atmosphere gets less dense so there are fewer air molecules that are able to collide with the surface and there are fewer air molecules above a surface as height increases so the weight of the air above it which contributes to atmospheric pressure decreases with altitude
how do we investigate elasticity?
measure natural length of spring when no load is applied with a millimetre ruler clamped to the stand.
Add mass to the spring and allow the spring to come to rest. record the mass and then new measurement of the spring. The extension is the change in length
repeat this until you have no fewer than 6 measurements
plot a force-extension graph .
It will only start to curve if you exceed the limit of proportionality
a larger force causes bigger extension and more work needs to be done
energy transferred in stretching equation?
E = 1/2 x K x X squared
energy transferred = 1/2 x spring constant x extension squared
(J) = 1/2 x (N/m) x (m squared)
what is the motor effect?
when a current carrying conductor is put between two magnetic poles, the two magnetic fields interact causing a force on the wire
what are the eight energy stores?
kinetic thermal gravitational chemical electrical electrostatic magnetic nuclear
what happens when a system (groups of objects your interested in) changes?
energy is transferred into or away from the system
some energy is dissipated and stored in less useful ways
what happens when a force moves an object?
when a force moves and object through a distance work is done on the object on the object and energy is transferred
what is force
a vector
when two objects interact they both feel an equal but opposite force - interaction force
describe moments on a spanner?
the force on the spanner causes the turning effect or moment of the nut which acts as a pivot.
