EOY Flashcards
Elastic deformation
When an object returns to its original shape when the stretching force is removed
equation with force, spring constant and extension
f = ke
equation for elastic potential energy
EPE = 1/2ke^2
Inelastic deformation
when an object does not return to its original shape when the stretching force is removed. Therefore, it is left permanently stretched
What is Hooke’s Law?
The extension of a spring is directly proportional to the force applied to it, as long as its limit of proportionality is not exceeded.
Limit of proportionality
The limit of proportionality is where if more force is added, the object will not return to its original shape when the force is removed
How to tell if object contains elastic potential energy?
it will return to its original shape
Explain why adjusting the ruler was important
to reduce error in measuring the extension of the spring
the ruler at an angle will make the measurements shorter
how to know if something is directly proportional
straight line
that passes through the origin
Technique to improve measuring extension
attach a pointer to the bottom of the spring
so it goes across the ruler scale
The stiffer the spring
the greater the spring constant, therefore more force is required per metre of extension
spring constant on a force-extension graph
is the gradient
steep straight line on force-extension graph =
small spring constant
work done is
the transfer of energy
Elastic potential energy
The energy stored in an elastic object when work is done on the object
types of errors
systematic error (zero error) random error
Newton’s Second Law of Motion?
When a resultant force acts on an object, it produces an acceleration (or deceleration)
What is Newton’s First Law of Motion?
If no resultant force acts, an object will remain stationary or move at a constant speed in the same direction
What is Newton’s Third Law of Motion?
When two objects interact with each other, they exert equal and opposite forces on each other
effects on stretched coil
the length of the coil has increased
length of the loops has stretched
spring has stretched
why are mean values given to 2 dp if results are 3 dp?
stopwatch reacts to 0.01 s
reaction time is less precise than a stopwatch
acceleration
the rate of change of velocity
change in velocity / time taken
velocity
the rate of change of displacement
accelerate
changed velocity
speed of sound
330 m/s
human walking speed
1.5 m/s
human running speed
3 m/s
human cycling speed
6 m/s
distance in a velocity-time graph
area under the graph
How to calculate reaction time
measure the distance the ruler falls before being stopped - the greater this distance the greater the reaction time
repeat measurements and calculate mean
why were anomalous result during reaction time
the student was distracted
stopwatch started before the computer test was started
How would you increase speed of a car
make it more streamlined
reduce the weight
increase power of engine
contact forces
forces that act between objects that are physically touching e.g. tension friction air resistance reaction force
resultant force
a single force that has the same effect as all the forces combined operating on an object
why does acceleration decrease even though the force remains constant
as speed increases air resistance increases
reduces the resultant force
why might an object continue at the move at a constant speed in the same direction
the resultant force is equal to 0
so the object will move at the same speed in the same direction
if an object is more streamlined
the air resistance is smaller
so the object can reach a higher speed
distance in a velocity-time graph
1/2 x base x height
Explain how the wheel can move at a steady speed and the capsules accelerate at the same time.
acceleration occurs when the direction of each capsule changes
acceleration is the rate of change of velocity
scalar quantities
have size (magnitude) but no specific direction e.g. speed, direction, mass, temperature & time
vector quantities
have both magnitude and direction
e.g. force, acceleration, displacement, velocity & weight
What are waves
are repeated vibrations that transfer energy from one place to another
What is the time period (waves)
time it takes for one complete oscillation
wave speed equation
wave speed (m/s) = frequency (Hz) x wave length (m)
Transverse waves
the oscillations are perpendicular to the direction of energy transfer
e.g. electromagnetic, ripples on the surface of water, vibrations in guitar strings and seismic S waves
Longitudinal waves
the oscillations are parallel to the direction of energy transfer
e.g. sound, seismic P waves
Non contact forces
don’t require the objects to be touching
e.g. gravitational, electrostatic and magnetic
get weaker the further the object is from the force
Ray diagrams (reflections)
angle of incidence = angle of reflection
normal is perpendicular to the surface of the material
point of incidence is where incoming ray touches the boundary
Specular reflection
mirrors are perfectly smooth - so boundary is flat
all the normals point towards the same direction
gives a clear image
diffuse/scattered reflection
when boundary is bumpy (e.g. paper)
normals are in different directions
you can’t see yourself
frequency of a wave
always stays the same - only the wavelength changes
when can waves change direction
when they change speed, moving from one medium to another
different mediums have different densities
if waves enter or leave the medium at right angles to the surface
they do not change direction (along the normal)
the higher the density of the material
the slower the wave will travel
Describe the movement of a wave refracted in glass
the wave hits the boundary at an angle
if it passes into a more dense medium (ie glass) then the ray will slow down and bend towards the normal
when it passes out into a less dense medium (ie air)
then the ray will speed up and bend away from the normal
wavefront
is an imaginary line that connects all the same points in a set of waves
they make it easier to visualise lots of waves moving together
Movement of wave fronts from air into glass
as the wavefronts move into the glass, they slow down
this causes the wavefronts to get closer together
which causes the wavelength to get smaller
this causes the wave to bend towards the normal
when waves speed up they bend away from the normal
compressions
regions where the vibrating particles are closest together
rarefractions
regions where the vibrating particles are further apart
The more densely packed the particles are
the faster the sound travels
sound waves need particles to be transmitted
when sound travels through a solid
they cause particles in the solid to vibrate
the vibrating particles will collide with their neighbours
which pass on the vibration
eventually the sound wave is transmitted through the material
sound waves are transmitted faster
through solid
slower through gases
Why can’t sound travel through a vacuum
there are no particles for the sound to be transmitted
wavelengths get longer as sound
speeds up
shorter as sound slows down
sound can be
reflected, absorbed and refracted
How do sound waves travel through an ear
sound waves travel along the ear canal and hit our eardrums
this causes the eardrums to vibrate
the vibrations are transmitted along the ossicles, through the semicircular canals and into the cochlea
the cochlea converts the vibrations into electrical signals, which are then sent along the auditory nerve to the brain and converted into sounds
higher frequency sounds
higher pitch sounds
lower frequency sounds
lower pitch sounds
Human hearing range
20Hz - 20,000Hz
why does human hearing range decrease
due to age
from the wear and tear of the cochlea and auditory nerve
ultrasounds
sounds that vibrate at frequencies above 20,000Hz
why do animals produce ultrasound
for communication
for echo location
why are ultrasounds partially reflected
some of the waves are reflected when they hit a boundary
whereas some are transmitted through (where they are refracted)
Uses of ultrasound
identify the boundaries within an object - which helps determine its internal structure check the quality of products in industry - if there is a crack, waves will be reflected back echo sounding (sonar) - when boats or submarines fire ultrasounds at the seafloor to find out how far away it is
P-waves (seismic)
longitudinal
travel through liquids and solids
faster than s-waves
S-waves (seismic)
transverse
travel through solids
slower than P-waves
P-waves through the earth
as p-waves are transmitted through the earth, they are refracted
the p-waves are constantly refracted throughout each layer (mantle, liquid outer core) as the density isn’t the same throughout a layer
battery
2 or more cells
potential difference
V = IR
current flows
from positive to negative (conventional current)
diodes
only allow current to flow in one direction
have a really high resistance in the reverse direction
only show when PD is positive
As potential difference increases
current also increases proportionally
assuming resistance is constant
assuming temperature is constant
if temperature increases
resistance increases
filament
as the current flows through the filament wire heats up eventually displays light however, this increases resistance so curve becomes less steap
series circuit
potential difference of the battery is shared across all components
current is the same
total resistance = sum of the individual resistance of all the components
greater the resistance the higher the voltage the component shares
parallel circuits
more components in parallel = lower total resistance
p.d. of components = p.d. of battery
current = sum of individual components
higher the resistance = lower share of the current
fuses break if
too much current
Ammeter
measure current
connected in series
Voltmeter
measure p.d.
connected in parallel
LDR
resistor dependent on the intensity of light
dark = high resistance
light = low resistance
uses of LDR
automatic night lights
burglar alarms
thermistor
resistance is dependent on temperature
hot = low resistance
cold = high resistance
uses of thermistor
car engines
electronic thermostats
Charge
measure of the total current that has flowed within a period of time
Charge equation
Q (coulombs) = I x t
why cant you increase current to increase power
high current = lots of heat (because of the resistance)
so lots of energy would be lost
Power equation
P = VI
Journey of national grid
power stations –> step up transformers
(increase the p.d. to 400,000 V)
—> pylons transmit the electricity —> step down transformers
(decrease p.d. to 230V)
national grid
It consists of a system of cables and transformers linking power stations to consumers (houses, factories and buildings).
why do step-up transformers increase voltage
to minimise energy loss during transmission
why do step-down transformers reduce voltage
to make it safe to use
alternating current
constantly changes direction
has 2 identical terminals
occurs when we use alternating p.d.
e.g. mains supply
direct current
constantly flows in the same direction
either positive or negative
has fixed positive and negative terminals
e.g. batteries and cells
oscilloscopes
display a.c and d.c current
electromagnetic waves travel at
3 x 10^-8 m/s in a vacuum
