Mocks FORGOTTEN

Question 1

Discharge through a resistor

Answer 1

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

Question 2

Explain discharges

Answer 2

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

Question 3

Remmeber bath graphs must add to v0 in the discharge at all times

Question 4

How to make the ac current more smooth

Answer 4

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

Question 5

How to find permitivity dielectric

Answer 5

Charge capacitor on diff voltsge and discharge on column enter and find gradient

Question 6

Potential at infinity

Answer 6

Is assumed to be 0

If energy is negative it means energy is needed to pull the, away = attractive force

Question 7

FOR OVERALL ENERGY DONE WITH POTENTIALS, HOW TO DO

Answer 7

Do it like see net potential change, multiply by charge, as going coming back releases energy etc

Question 8

How ti find net potential?

Answer 8

Find potential caused by all particles and add them up like a scalar

Question 9

Remember in uniform plate etc, thr electric field may be the same at each point, but depending in the radius, what about the voltsge?

Answer 9

This will change, btw more positive voltsge = positive olate

Question 10

Why is energy independent on path followed but not of start and finish

Answer 10

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

Question 11

Magnet scale experiment

Answer 11

Magent on scale with wire through them, based on direction can work out force and thus flux density

Question 12

Remmeber a charged particle in MAGENTIC field doing circular motion, what two equations can we equate

Answer 12

BQV=MV2/R

Question 13

In a velocity selector

Answer 13

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

Question 14

How does this work in mass spectrometers

Answer 14

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

Question 15

How is energy conserved when generating current?

Answer 15

Force used ti lift up causes electrons ti move by Fleming rule, and thus generate current, so energy is conserved

Question 16

Emf

Answer 16

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

Question 17

I why are the south pole thing different

Answer 17

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

Question 18

If you dripped a wire and let it full under weight through a MAGENTIC field, eventual,y

Answer 18

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

Question 19

How ti model ac generator

Answer 19

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

Question 20

Back emf

Answer 20

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

Question 21

How to increase effeicny in transformers

Answer 21

Trandoremrs aren’t effeicny because of eddy currents being produced, MAGENTIC field assumed not transported , resistance

1. Soft iron core
   2) low resistance wires
   3) laminate core made from layers and insulation in tween ti prevent eddy current

Question 22

How can decya be described as random and spontaneous d

Answer 22

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

Question 23

What is activity

Answer 23

Rate at which nuclei decay

Question 24

Equatuin fir activity

Answer 24

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

Question 25

As n decays exponentially what else does

Answer 25

A proprtinsl to N so A must too

If

Question 26

How to do change if activity

Answer 26

Ti find INITAL i activity, find the lambda, have the N , it’s lambda N

Then put it into activity ewauriom

Question 27

How does CARBIN dating work

Answer 27

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

Question 28

To have suitbsle thing for dating

Answer 28

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

Question 29

What happens with annihilation

Answer 29

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

Question 30

What happens in pair production

Answer 30

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

Question 31

What happens in cern

Answer 31

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

Question 32

What is mass defect and binding energy

Answer 32

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

Question 33

Why does a bigger binding energy mean more stable

Answer 33

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

Question 34

Why on the graph does energy get released when nuclei become higher binding energy

Answer 34

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

Question 35

Explain the graph

Fusion fission

Answer 35

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

Question 36

How fission work

Answer 36

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

Question 37

What is Jon if moderator

What do coolant

Control rods

Answer 37

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

Question 38

Why is fission dangerous

Answer 38

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

Question 39

How does fusion work

Answer 39

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

Question 40

Hydrogen proprtinsl proton chelae mainly occurs

Answer 40

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