Physics Flashcards
what is temperature the measure of ?
average KE of particles in a substance
0 kelvin is how many degrees Celsius ?
-273
what is heat measured as ?
Joules
what is heat a sum of ?
kinetic energy of all particles
what does increasing distance between particles do to the bonds?
decreases the strength
why does the temp of a substance not increase during melting/boiling ?
additional energy used to break intermolecular bonds
what is latent heat ?
the amount of energy needed to change the state of a substance
name the 4 factors of condensation
temp / surface temp / airflow / density
why is rate of condensation higher with greater density ?
particles closer - stronger forces
what is evaporation ?
liquid changing to a gas without boiling (average KE of particles is below BP)
individual particles only evaporate if …
- high KE
- travelling towards surface
name the 4 factors of evaporation
temp / airflow / density / surface area
define conduction
process of vibrating particles passing on their KE to neighbouring particles in a material
why are metals good conductors ?
ions are tightly bound
free electrons can transfer energy
why are non-metals not very good at conducting ?
no free electrons
what is a fluid ?
substance with no fixed shape
what is convection ?
transport of heat energy through a fluid
why does hot air rise ?
less dense due to particles moving further apart from each other
what is the term for the cycle of hot air rising and cold air replacing it ?
convection currents
what is radiation (heat) ?
heat transfer from the emission of electromagnetic waves from warm bodies
why can radiation travel through space ?
does not require a medium
what is power the rate of ?
rate of energy change
power =
energy / time
what are the best absorbers and emitters of radiation ?
dark matte objects
what are the worst absorbers and emitters of radiation ?
bright and glossy objects
give the factors of heat transfer
SA / vol / material
list the features of a vacuum flask
- vacuum between container and flask
- inside and outside are shiny
- insulating foam
why do warm climate animals have large ears ?
increases SA so can radiate more heat
density =
mass / volume
what is buoyancy dependent on ?
whether the object is more/less dense than the fluid
how to find volume of irregular solid?
place in beaker of water - find volume of displaced water
what is propagation direction ?
the direction a wave is travelling
define amplitude
maximum displacement of wave from resting position
define frequency of wave
no. of waves produced per second
1 Hz is ..
one wave per second
give 3 examples of transverse waves
- electromagnetic waves
- seismic S-waves
- slinky up and down
in which direction do transverse waves vibrate ?
perpendicular to propagation direction
in which direction do waves vibrate ?
in propagation direction
give 3 examples of longitudinal waves
- sound waves
- seismic P-waves
- slinky forward/backward
what are mechanical waves ?
require a medium to travel through
wave speed =
frequency x wave length
wave speed measured in …
m/s
time for single oscillation =
1 / frequency
what is the law of reflection ?
angle of incidence = angle of reflection
what is refraction ?
change in direction of a wave as it travels through a diff object with a diff refractive index
what causes refraction ?
diff refractive index causes increase/decrease in speed, causing to bend away/towards the normal
when will a wave not refract ?
at a right angle to surface
what is dispersion ?
refraction of light through a prism causing light to be split into diff colours
sound travels fastest …
in solids
what is pitch dependent on ?
frequency of the sound waves
ultrasound waves have a frequency of above …
20 000 Hz
infra sound waves have a frequency of below …
20 Hz
what is volume dependent on ?
amplitude of sound waves
what doe the EM wave lengths range from ?
10^-15m to 10^4m
at what speeds do EM waves travel through a vacuum ?
all travel at speed of light
what is speed of light ?
3 x 10^8 m/s
how are long radio waves able to travel long distances ?
long wavelengths can diffract
stopping distance =
thinking distance + braking distance
force =
mass x acceleration
what is static friction ?
between stationary object and surface
work done =
force x distance moved (in direction of force)
what are the units for work done ?
joules
work done is the same as …
energy transferred
weight =
mass x gravitational field strength
momentum =
mass x velocity
what are the units for momentum ?
kg m/s
force (momentum wise) =
change in momentum / time
what are the two equations for Power =
work done / time
energy / time
what is measured in watts ?
power
what is a watt ?
one joule transferred in a second
Kinetic energy =
0.5 x m x (velocity)^2
when stopping a car…
KE transferred =
work done by breaks (Fd)
Gravitational potential energy =
mass x g x height
name the 9 different energies
kinetic, heat, light, gravitational, chemical, sound, electrical, elastic, nuclear
efficiency =
useful energy output / total energy input
how can wasted energy be reduced ?
heat exchanger used
what is electric current ?
flow of charge
potential difference (voltage) =
energy / charge
what are the units for potential difference ?
volts
what are the units for charge ?
coulombs
charge =
current x time
what are the units for current ?
amperes (amps)
other potential difference (voltage) =
current x resistance
what are the units for resistance ?
ohms
what does a variable resistor do ?
alters current flowing through the circuit
what device measures voltage ?
voltmeter
what device measures current ?
ammeter
for an ohmic conductor graph, what is the resistance ?
1 / gradient
what is charging by friction ?
rubbing insulating materials and causing electrons to move
when polythene is rubbed against a cloth duster, which way to electrons go ?
electrons move from duster to polythene
how does static electricity help electronic paint sprayers ?
- paint charged, droplets repel, fine spray
- surface of object is opposite charge, attracts, even coat
what does cell do in a circuit ?
supplies with power provides voltage (poten. diff.) to move charge around circuit
current =
voltage / resistance
LED stands for …
light emitting diode
LED emits light when …
current flows through it
what do fixed resistor and variable resistor do ?
oppose flow of current, helping to set a value for current
what does a thermistor do ?
changes resistance according to temp
voltmeter is always placed in …
in parallel with components
ammeter is always placed in …
in series with components
what does a LDR do ?
changes resistance according to light shone on it
what is a series circuit ?
components connected in a line
if there is a break, charge stops flowing
describe the current in a series circuit
all the same throughout
A1 = A2 = A3
describe the voltage in a series circuit
shared between components
Vtotal = V1 + V2…
describe the resistance in a series circuit
shared between components
what is a parallel circuit ?
components connected in loops, therefore if one is broken, charge is unlikely to stop flowing
describe the current in a parallel circuit
shared between components
describe the voltage in a parallel circuit
all the same throughout
what is electromagnetic induction ?
production of a voltage across an electrical conductor in a changing magnetic field
a voltage can be induced when :
- magnet moved into coil of wire
- electrical conductor moved in a magnetic field
direction of voltage or current can be reversed by :
- changing direction of movement of conductor
- changing direction of magnetic field
when is an alternating current (AC) produced ?
when magnet/coil moved backwards and forwards (keeps swapping direction of voltage)
how can voltage be increased (4 ways)
- move magnet faster
- use stronger magnet
- increase no. of turns in coil
- increase coil area
what is direct current (DC) and what is it produced by?
a battery produces this current, which is always in the same direction
give order of flemmings left hand rule
force direction - magnetic field - current direction
direction of magnetic field is …
north to south
direction of current is …
positive to negative
what is a step-up transformer and how does it work ?
changes a low-voltage supply to a high - increases voltage - more turns on secondary than primary coil
what is a step-down transformer and how does it work ?
changes a high to low voltage - more turns on primary than secondary coil
why is soft iron core used for transformers ?
easily magnetized, so transfers magnetic fields from primary to secondary coil
describe how a transformer works (4 steps)
- primary coil connected to AC supply
- changing current produced changing magnetic field in primary
- induces an alternating voltage in secondary through iron core
- induces AC in secondary
what do Vp and Vs mean ?
primary/secondary voltage
what do Np and Ns mean ?
number of turns on primary/secondary coil
give the ratio equation for transformer
Vp/Vs = Np/Ns
how efficient are transformers and what does it mean ?
nearly 100% so
power in primary = power in secondary
what power equation to use for ideal transformer equation ?
P = IV
give the use for step-up transformers
produce high voltage for transmission of electricity to minimise energy loss by heat
give the use for step-down transformers
reduces voltage to a safer value to be delivered to homes
give the formula for power loss due to resistance in cables
P = I^2 x R
what is the letter that represents charge ?
Q
what is ionisation radiation ?
radiation that can cause other particles to lose electrons
state the nature of alpha radiation
2 protons and 2 neutrons
state the nature of beta radiation
an electron
state the nature of gamma radiation
an EM wave
state the charge of alpha radiation
+2
state the charge of beta radiation
-1
state the charge of gamma radiation
0
state the ionising effect of alpha radiation
very strong (due to size)
state the ionising effect of beta radiation
moderate
state the ionising effect of gamma radiation
very weak (tends to pass through)
state the penetrating effect of alpha radiation
slow moving so can be stopped by paper/skin
state the penetrating effect of beta radiation
moderate, blocked by thin plate of metal
state the penetrating effect of gamma radiation
high penetrating, blocked by thick metal plates
give a use for alpha radiation
smoke alarms
give a use for beta radiation
monitoring thickness of materials
give 2 uses for gamma radiation
treat cancer
sterilise food / medical equipment
what is fission the term for ?
splitting an atom into two smaller atoms
what causes nuclear fission ?
slow moving neutron hitting into a large isotope
what are the units for radioactive decay ?
Becquerel (Bq)
what does 1 Bq represent ?
one nucleus decaying per second
state the two factors of decay rate
- the element
- how many undecayed nuclei in the sample
