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