Mocks FORGOTTEN Flashcards
Discharge through a resistor
When switch pressed assume all the voltsge fine ti fapsciatcne so INITAL charge can be worked out, all the voltsge goes to resistance so INITAL current can be found out
Now as charge decreases , so does pd, and thus current too
They all proprtinsl, so all exponentially decay
Explain discharges
Initially at t= 0 all voltsge goes to resistor
As time goes on and charg builds up in cascpaotr, it has own of, and own current so current in circuit decreases exponential
As v in resistance proportional to current, it will decreases exponentially
And charge and voltage is governed by 2nd law Kirchhoff, so total v = increase
Remmeber bath graphs must add to v0 in the discharge at all times
How to make the ac current more smooth
Make thr time constsnt less, so thst it discharges quicker, and if this is much more less than the frequency of thr ac voltsge, then it will be quite smooth
How to find permitivity dielectric
Charge capacitor on diff voltsge and discharge on column enter and find gradient
Potential at infinity
Is assumed to be 0
If energy is negative it means energy is needed to pull the, away = attractive force
FOR OVERALL ENERGY DONE WITH POTENTIALS, HOW TO DO
Do it like see net potential change, multiply by charge, as going coming back releases energy etc
How ti find net potential?
Find potential caused by all particles and add them up like a scalar
Remember in uniform plate etc, thr electric field may be the same at each point, but depending in the radius, what about the voltsge?
This will change, btw more positive voltsge = positive olate
Why is energy independent on path followed but not of start and finish
Energy can start and finish at the same point but transfer energy
But if two particles of different charge take same path energy transferred will be diff
Magnet scale experiment
Magent on scale with wire through them, based on direction can work out force and thus flux density
Remmeber a charged particle in MAGENTIC field doing circular motion, what two equations can we equate
BQV=MV2/R
In a velocity selector
A megtnic fied is applied and electric field and a charged particle will feel a force by bothl
It is only when these are equal that the particle won’t be deflected and can leave
This happens when EQ = BQV
and thus V = E/B fields
Thus only at a DLECIFIC VEOCLITY will it be able to go through
And so by using v selector you can guarantee a veocloty to go through
How does this work in mass spectrometers
First a v selector used to ensure same veocloty
Then another electric field applied outside, so thst it experienced circular motion . In this case bigger particles will experience more radius change and so detected differently snd can pick up
This is using BQV = mv2 /r equation
How is energy conserved when generating current?
Force used ti lift up causes electrons ti move by Fleming rule, and thus generate current, so energy is conserved
Emf
Is id diced whenever there is a change if MAGENTIC flux lonkage
The emf produced will be ina. Direction to oppose the change that caused it = lenzs law
I why are the south pole thing different
Because attraction would mean that electric,s energy is genrwtored out of nowhere
So pulled away from coil it has ti do work against, if it repelled agsin accelerating for vibes
If you dripped a wire and let it full under weight through a MAGENTIC field, eventual,y
It would reach a terminal velocity as emf also = BLV, so an increase in v means emf means firce so slows down etc, everntusk,t temrknak vecoloty when the firce = weight
How ti model ac generator
When ti ever ticks the theta is 0 so cos theta is maximu. As everything stays the same the flux linkage depends on theta ad the area is changing , so yeah
But when max flux linkage, change if flux is actually the smallest , so emf is 0
When flux is 0 change is max so highest
Thus the emf groan is negative flux linkage graph
As this also depends on frequency, max emf = BANw
And emf - max sin theta
AND CAN REOLACE THETA WITH WT
Back emf
Is produced when force is produced from morose effect creates its own current backwards
Thr magentiude on this depends on frequency if roataion of everything else kept constsnt is putting weights on it slows it down. So to make voltsge max go to motor, need frequency the slowest
For a wire suddenly turning off, the MAGENTIC field suddenly collapse in a short amount if time , so change of flux is large and thus a current is produced in a. Direcitin ti increases the MAGENTIC field
I’m this case B RAPIDLY CHANHES
Huge emfs caused changed of flux over very small time , thid thou flaky hsooejd when B goes to 9, domt forget
How to increase effeicny in transformers
Trandoremrs aren’t effeicny because of eddy currents being produced, MAGENTIC field assumed not transported , resistance
- Soft iron core
2) low resistance wires
3) laminate core made from layers and insulation in tween ti prevent eddy current
How can decya be described as random and spontaneous d
Random = we can’t predict the next nucleus to decay
- each had the same chance
Spontaneous
- putting another won’t change chance
External factors won’t like pressure either
What is activity
Rate at which nuclei decay
Equatuin fir activity
As the rate if change if decay is proprtinsl to how much left, then activity proprtinsl to N and so A = KN
Ln(2) / half = k
As n decays exponentially what else does
A proprtinsl to N so A must too
If
How to do change if activity
Ti find INITAL i activity, find the lambda, have the N , it’s lambda N
Then put it into activity ewauriom
How does CARBIN dating work
As all living beings have Carbkn 14 and 12, when living this ratio is constant
However cwbrknn14 decays over time
So in a sample of human, you know how much CARBIN 14 there isn’t
If you know thr half life, you can find lambda , and out in equation, comparing ratios, and work out time it’s been
To have suitbsle thing for dating
Must half half life decent enough ti have been present in some quantities when it was around
Cabrini dating limitation asusmes ratio still constant , + measuring csbdknn14 hard because matches background radiation
What happens with annihilation
Two antimatter disseparr, so equal mass, so change in a,so = 2 M , and resulting energy difference equal to that, so minimum energy the ohkton must have csn be determined
What happens in pair production
This case a knot in kf energy vanishes and thus mass is created , as two created, you can work lite minimum energy if both if you know the particles
What happens in cern
High speed protons crash into each other and new particles are made, this is because kinetic energy evolved in crash creates mass
Mass of new particles = kinetic energy of colliding
What is mass defect and binding energy
Mass defect is difference in mass when atom nucleus is split into nucleons ..
As this required energy ti break bind, mass after is BIGGER. The energy that is rewuired / energy released when back together is called binding energy
Thud thr mass defect (change in mass) = binding energy c2
Why does a bigger binding energy mean more stable
It means more nearby needed to break apparat, so bigger binding energy ,sans more stable nuclei
Here bigger isotopes will have more binding energy right, that’s why we divide by Niue,one ti see which nuckei have the higher binding energies
Why on the graph does energy get released when nuclei become higher binding energy
This because think about it, the difference in binding energy = energy released as rhe nucleons get CLOSER TOGETHER , the closer they get, the more energy released and more energy needed to pull them apart
So as they increase be, it means they closer together now and energy is released
Explain the graph
Fusion fission
Going ti ruin 56 bringing energy generally increases, more so for alpha
To the right going to it it also increases too
When fusion takes place, two low mass number nuclei fuse to become a bigger one, and thus one with HIGHER BINDING ENERGY . We just said that higher binding energy releases energy
- fission, large nuckei becomes a smaller nuckei closer to iron 56, agsin with HIGHER BINDIJG ENERGY, so energy is released agsin
However fusion binding energy increase is much more crash than fission so way more needy released - even in nuclear decay, summof binding energy larent to child is much higher now, especially when alpha so high. It decayed into something stringer attctehd together , so energy released in process,s this is why energy released in nuclear decay too
How fission work
Some sort of uranium is given a slow movijg neutron induced , and this causes it to become an isotope more likely to decya,meh in decays into two atoms + 3 fast moving neutrons, and releases energy . As a result mass decreases ,
Now if all three fast neutrons were slowed down then a chain reaction would occur as 3 more fissions induced and this would keep happening, nuclear bomb.
We have equipment in place to slow it down and Mike it one slow neutron survived per generation , controlling the increases of energy
What is Jon if moderator
What do coolant
Control rods
Badislcllt to slow done the neutrons, because it would jsutnbkundce if uranium atoms without much loss of energy and unlikely to be absorbed.
But when collide with deuterium or CARBIN, a lot of energy lost, so it slows down.
Thus moderator typically water of csbrknn
- here the coolant which is used ti remove thermal energy from the actual reactor is typically thr coollant too
Control rods are boron rods that readily ABSROB NEUTRONS THST CSN BE CONTILLED IN OR OUT TO LOMIT AND EXACTLY PRODUCE ONE NEUTORNNOER GENERTWIOM
Why is fission dangerous
Plutonium 239 is eventually made agterbdecays
This half life is insane and very toxic and radioactive
Main stress is cleaning radioactive wstee, must put in a place ehsihc won’t effect anything at all
How does fusion work
It’s the fusing of two small nuclear mass nuclei into a bigger one . The energy released is due to the mass loss as then handing energy increases a lot
- here the only way to get the nuclei so close so thst they can be ABSORBED INTI THR STRING NUCLEAR FORCE.
Is through high tmelrwured and pressures which will overcome the electrostatic forc .
These conditions thpically found in stars and so hard to replicate on earth
Hydrogen proprtinsl proton chelae mainly occurs
Hydrogens fuse and produce a deduce room, this produced enormous energy usign graph hydirgend have 0 binding energy
Then the deurtoeum tracts with another hydrogen to make 3/2 helium releasing more energy
Then two of these combine to make a 4 2 helium and release 2 more protons which go again
Obvisouly heavier atom the more harsh conditions you need, that’s why stars cuelc do all hydrogen first before their fire changed etc
