paper2 dk Flashcards
how to vary current
change no. cells
using a variable resistor
why is there a net transfer of energy/heat
temp outside > inside so energy is transfered
method to measure how current varies with voltage
- record voltage
- record current
- change V using a variable resistor
- repeat and average
- plot graph of V and I
advantage of high voltage
high V means low I as VI = VI
less thermal energy tranfered to surroundings
less energy lost - more efficient
why waves arent affected by doppler effect
- no relative motion between the objects
- no wavelength change
why particles from a higher pressure chamber reach a higher height
higher pressure leads to higher speed
so has more KE
have same decceleration
takes longer to reach 0 due to higher speed
so travels further
why the sun appears not circular when close to horizon
light from diff parts of he sun refract different amounts
refraction is large when the sun is closer
why a ray doesnt chnage direction
i = 0 and i = r so r = 0
fusion
2 light nuclei
fuse to make a large nucleus
release heat energy
loses mass
E = mc^2
moderator
slows neutrons
made of graphite
control rods
absorbs neutrons
made of boron
how a transformer works
steps down V
- current in coil makes magnetic field
- current alternates
- field changes dircetion
- core strengthens field
- field cuts coil inducing V
why is transformer core made of iron
easily (de)magnetised
magnetic field is alternating
explain why metal ball floats over a charged metal dome and reaches a maximum height
once too far the repulsive force is too weak so it stops being repelled
- weight acts down
- W> repulsion
- slows down and KE decreases
- GPE increases
- until KE is 0 at max height
- and only weight acts
nucleus moves left in amagnetic field - how a nucleus behaves to experience this
must be charged particles moving at 90 to the magnetic field and moves down
why fusion at high temp/pressure
- same chrge nucleus so repel
- high temp/ pressure needed to overcome repulsive force
- not enough KE
momentum
remember to use + and -
disadvantages of wind turbines
- noise pollution
- ruin habitat
how attraction affects momentum
- momentum increases as closer due to force of attraction increasing so velocity increases
how transformers are useful in transmission
step up
- increase voltage
- lower current
- less energy lost as heat
- more efficient
step down
- voltage decreased for safe use
harmful effect of infrared vs microwaves
skin burns
microwaves - internal heating of body tissue
why is there no radiation
similar temps so no radiation - or solids/ liquids
why not newtons 3rd law
not same type of force eg weight is balanced by gravitational force
acts on a single object not diff objects
how is an electromagnet formed
coil of wire
around an iron core
current in the wire
creating magnetic field
which store decreases in nuclear fusion
nuclear
why stop clock not used and data logger used instead
human reaction time
- too small a value wpuld be skewed too much
principle of moments
sum of ACWM = sum of CWM in equilibrium
why diff gradients in a changing state graph for diff objects
- diff temp change in same time
- diff specific heat capacities
what info spectra gives about a galaxies movement
all are moving from centre
spectra is red shifted and blue shifted
shows expanding from single point
galaxy is spinning
why H, He and C are found in spectra
He made in fusion
H makes up stars and used in fusion
C is formed from fusion in red giants
why difference in measured frequencies of sound for diff buzzers
frequency decreases
due to doppler effect
wavelength increases as s= fY
decrease in freq of B is 2 x the decrease of A as B is closer to the source
how to measure mag field strength - using hall probe
- idea of measuring mag field at different distances - use ruler
- idea of repeat and average
- distance is independent variable
- mag field strength is dependent variable
- current is a control variable
- reference to suitable second control variable
e.g. coil (spacing or turns), the rest of the apparatus
