jan mocks dk paper 2 Flashcards
electron gun
- speeds up electrons with accelerating pd
- thermionic emissions cause electrons to escape
- attracted to anode
internal resistance
resistance due to the material the battery is made from
causes energy to be wasted as heat
battery charger
connect a charger with a higher emf to the battery
forces current into the battery to charge it
potentiometer
varies voltage
vary output V from fixed supply - 0>maxV
rheostat
can be connected as a variable resistor - good if large I needs to be varied
or can be connected as potentiometer to vary V - currents are very small
intensity prop to
A^2
v^2
KE
v prop to A
how signals are sent
amplitude modulated
- amplitude shows messgae
freq modulated
- freq of wave shows message wave
arials
- mesh reflects signals to front
- circular rod picks up signal (1/2λ tall)
- other rods boost signal (1/2λ apart)
- adjacent emitters alternate between hor and ver to avoid interference if they overlap signal areas
measuring λ of microwaves
- probe is moved from central maxima along
- positions marked and path diff determined
- each max can be used to calc λ then average
youngs double slit - set up + risks
- pass through colour filter (monochromatic)
- creates fringes
risks - dont look at laser
- remove reflections
- dark room
diffraction grating
more slits = narrower bands
d sinθ = nλ
nmax = d/λ
photons
quanta of energy of electromagnetic radiation
LED
- electron transferred across pd
- gains energy
- emits energy as a photon
eV = hf
plot eV against f
grad = h
conc for photoelectric effect - not wave theory
- only emit above threshold freq
- intensity doesn’t effect energy
- no. electrons prop to intensity after f>f0
- electrons emitted have a variety of KE up to max
- max KE ^ with f
find max KE of emitted electrons
find stopping voltage
eV = max KE = hf -hf0
diffraction rings
grating
nλ = d sinθ
if v ^ rings get smaller/ closer
d = spacing between atoms
λ = h/mv
curved accelerators
- increased r = increased acceleration
- curved - particles accelerate through gaps more than once
+ particles can reach higher energy - keep going round
+ alternating field keeps giving more energy
hall probe
- measures mag flux density
- Vh = BI/nbq
where b = thickness
hall effect
- pd created across a semi conductor due to mag field across it
- when wire in field - force occurs due to field -as electrons move down
- electric field created
- when eq F(E) = F(B)
- travel in straight line
lenz law
direction of induced emf due to change in flux linkage
is such that it would oppose the change producing it
ac generator
- consists of coil spun in uniform field
- when coil spins at steady rate flux changes continuously
- when at θ linkage = NBAcosθ = NBAcoswt
- emf = NBAw sinwt
max emf = NBAw
emf in terms of v
v = BA = BLs/t = BLv
why transformers not 100% efficient
- loss from current flowing - resistance causes heating effect Ploss = I^2R
- loss from magnetic losses
- loss from magnetising increases temp
- eddy currents created in iron core due to magnetic field causing electrons to move
how to make more efficient
- decreasing resistance
- prevent coils close to soft core
- use material easily magnetised/ demagnetised
- laminated (insulator between layers)
