How To Answer Any Q

Question 1

First look at the question with further physics and ask for assumptions

Answer 1

So assume no evaporation occurs, assume same mass distribution and g is constsnt etc

Question 2

Then draw diagrams to make it easier in different cases

Answer 2

For example draw a diagram of befor and after WITHOUT ANY PHYSICS FIRST

Question 3

Then make a sense of what’s happening

Answer 3

So talk through thoughts in head and what you expect to happen before it acc happens, and what your answe will depend on
Write a statement and move in

Question 4

Now do the physics and a,the, state principles , lay down variables and make equations

Question 5

Now if it reaches state,ent, then come to a conclusion

Question 6

Remember world done = force x distance of object moved in direction if force

Answer 6

Thus f sin theta
Always draw force diagram first

Question 7

Young modulus

Answer 7

F=kx is booked law, a spring extension is proprtinsl to firce applied until a limit of proptinal it’s

Then the gradient is spring constsnt or stiffness

In parallel springs , as force is halved or sitirbuted, the new spring constsnt is addition , as half force given ti both
But series same force given to both so they both extend, so series spring constsnt gets smaller using parallel rule

Extends until proprtinsl limit, then elastic limit, then after that I elastic and any work done area is used to deform the thing = plastic ferirmatjin

Energy = 1/2 f x , which is 1/2 kx2 if sun f for kx

It’s the same for young modulus, 1/f fx m need to rearrange those

May have to it egrets

Question 8

Deforming and loading

Answer 8

Loading is what happens when firce applie,d unloading when removed

For a spring this should be same, until you go last elastic limit, it will return to deformed area because of atom binding and area is used to deform

Rubber is hysterics graph, it doesn’t deform, but energy is given out as heat when deforms ti orig a, kefntg

More work is done when stretching, then is r,erased when letting go, thermal energy released, so rubber thing, need to cool so pressure equalsie

Question 9

Young modulis

Answer 9

Stress / strain, where stress is force / area and strain is x/ L
For a metal
This is a prototype thst regsrdless of dimensions will be a thing for each object, a special protects
- originally it extends according according ti hooked law, then it no longer portions until it reaches a point. Elastic limit
- here there are yield points, where the alloy big atoms unlock from small, leading ti accelrwtion and thus easier to extend so less force so goes down, then it locks again
- now it just oaksticlsly deforms until UTS point, this is max stress it can take before breaking now
- past this, it thins necking, similar to where plastering pulled, and it stenches very easily so goes down u til ti just breaks

Question 10

Other stress stain groans

Answer 10

Iron and glass

They just break , and don’t reach any yew points
For metal

Okay and area is energy density, energy stored per unit volume = similar to stress so if they give modules can work spout strjan

Question 11

Is it always good to have high young modules for enginerring?

Answer 11

No = aerolpkane wants made form aluminium alloy that is string and stiff so high young modules

And for example car numbers need to deform quick ti reduce time for change if moentum

Question 12

Normal Newtonian pair ?

Answer 12

You exert reaction force down and it enters one up

Reason why no accelrwtion this plane is because nrowml from ground is equal to weight

Until there is accelrwtion snd this changes

Question 13

When you jump to earth whey doesn’t earth move to you

Answer 13

It does
But because earth inertia so big, it resists this accelrwtion more and doesn’t seem like anything baoloend

Question 14

Momentum

Answer 14

Is a vector quantity
Is always conserved
Total momentum before = momentum after

Principle is for a system of interacting objects, the total momentum in a specified direction and

plane is constsnt, as long as no external forces act or the system !

For a gun providing no external force, the bullet and gun is the system with koentum zero

When you shoot buller in velocity, go;will she to recoil so monetum is conserved.

Elastic collision is where kinetic energy is conserved , and I least if is where ke isnt, transferred to other forms

In an elastic collision, one will stop and otherkeep going, or two at same speed will collide and bounce off

Easktic only if a same mass I believe

Both cases total energy still conserved yh , and momentum tok ofc

Second law is rate of change if meontu

When crash your momentum gins go from something to 0 confirmed, you want the time taken to be huge so that force is less, so air bags seatbelt bumper deform to save you

Question 15

He is koentum always conserved in collision or two interacting

Answer 15

Basically two interacting, the net force of the overall system is 0

So the change if momentum rate must be 0

Thus change in momentum gotta be 0, so koentum is conserved

Question 16

Impulse ideas

Answer 16

Impulse is fxt which is change if koentum

This is always conserved
So momentum conserved and you can use impulse to find change of koentum

And momentum conserved in all planes so csn make equations, if momentum in y plane wa s9 etc

Question 17

Cruet snd mean drift velcoutn

Answer 17

Current is the rate of flow of charge, can be ions etc, in which charge is x2

Ammeters no resistance so max current can go through ideally

cruet = elementary charge x mean drift velocity x number density (which is number of FREE ELECTRONS PER CUBIC METER)

So things with higher number density will tend to have higher current, this is the conductors, semi in middle and insulators bottom
And so when number density increases, when temperature breaks covalent bonds in the semiconductors, current increases and resistance thus decreases

Kirchhoff first law is that current going into a jus ti on = ti current out, so if there is no junction current same ebeyrbwer (series circuit )

This related to conservation of charge, where the charge can’t be created or destroyed, charge is fielded as charge CANT be created, the charge going in = charge going out

Question 18

Volt

Answer 18

Remember batteries is vector addition, they cancel out if 3 and two one way and one other

Don’t conritbute ti viktsge but do for total internal resistance!

Voltmeters have to have infinite resistance so max voltage goes through them and no current goes through the voltmeter jr self

Emf is work done to charge carriers and pd is work done by charge dwrrueee

Emf = pd in a closed loop = Kirchhoff second, and relates to conservation if energy

Question 19

Thermionic emissions do the electron gun, how does it work?

Answer 19

Small filament heated by an electric current, this gives the electrons enough kinetic energy to escape the surface of the metal = thermionic emission

If the filament is connected to an anode, filament becomes the cwbtide and if in a vacuum, the electrons will then go towards anode
If hole in cathode then you have a beam of electrons

Where the electrical work done given to vQ = keintic energy

Question 20

Resistance and ohms law

Answer 20

Ohms law is that fir a wire metal at constsnt TEMPERTAURE (because then resitivity changes), the current of the wire is directly proptinal to voltsge

Okay if you have something insulate, more current hat goes past the current will heat snd insulator keep heat, this increase this area where the metal positive ions gain kinetic energy and can start to vibrate, acting as an impeding to current flow, this means less current fir same voltage so resistance increases

Question 21

IV characteristics

Answer 21

Fixed resistor = straight, obeys ohms law , and gradient 1/ is resurgence

Filament lamp, as voltage uncrease and current increase heat increases in metal filament which causes vibration and impediment so less current and more resistance. More resistance = less gradient so decreases

Question 22

Diodes

Answer 22

On,y allow curetnone way, so on or off, so controls all electrics

LEDs emits light when conduct through the,

Vi graph is that reverse it blocks do infinite resistance, and takes a bit of current before resistance evituskky tends to 0, this often threshold pd

Question 23

Differn tmwteirals have different resitivities which allows different resistances , but this changes at differnt temps

Answer 23

Yh for semi it decreases allowing more current

Question 24

Thermistor and ldr

Answer 24

Negative temp cieffeicnr means as the temp goes up reistsnce decreases, this because number density increases more current and so less reistsnce
Same for light

Graph of restsice. Against temp is 1/x , inversely proptinal

If charvwtristic if wnthermsitor

As current increase,so heat increases, which increases temp and thus decreases resistance so looks like it goes to infinty tan graph

Question 25

Internal resistance

Answer 25

When batteries in series, the emf adds but so does the reistsnce, meaning you can get more pds

When in parallel, emf same, but rest is net decreases, so higher currents

For different things differnt used

Power is the thing thst kills

Question 26

Potentiometer

Answer 26

Use potentiometer to measure v and I as you can range the whole voltage

Closer you bring it so length of resistor in wire increase,s more closer to VIn, assuming that’s only comoiej t

Better because
- compact, change in restsnce linear log
- can vary thr whole thing

Otherwise thou want something somewhere in between for maximum range

Question 27

Remember in refraction what happens to wave,wntgn

Answer 27

Remember that refraction is that another mdieum is more dense optically and thus speed is less in there, but for same frequency this reduced wavkentgh and so waves become closer together and bend towards normal!

Deep water faster

Diffraction is oheneomea thst when a wave goes past a gap similar to their wavelength, it spreads out around

The more smaller the wavelength is compared to the gap the more diffraction is observed

This is why in young modules you want INITAL slit to be quite thin to ilium it’d other two slitd

Polarisisitom is confining electromagnetic or transverse waves into one plane, can’t be log tofunal

You’ll have a filter thst will do this and all components of it into that plane too, dlr elstive intensity falls

This is proptinal to cos theta maybe?
Anyways intend to I= power /area, where r is radius as it radiates radially, and it’s area of a sphere 4 pi r2

Intensity is then proptinal to amplitude sqaured too, and amplitude is the measure of energy
So when amplitude falls, the intensity falls too and thus becomes whiter or louder

Aroeals are often polarised to get different planes things so they don’t interfere as much