Physics Pop Quiz

eZe^

f Proportional (mv - mu)/t (cant be bothered with notation, we all know it!)

f Proportional mv - mu / t
f Proportional m (v - u) / t
f Proportional ma
f = kma
let 1 newton be the force that gives a body of 1kg and acceleration of 1m/s^2
therefore k = 1

therefore f = ma

carlowboy

jmccrohan wrote:

I wrote that in my mock and got nothing. its

t=T-273.15

As did I but I got marks....then again I did write the notation with it. I guess I couldn't have been arsed a minute ago!

Jonathan

carlowboy wrote:

Tell me newton's second law and derive the subsequent equation from it. (a lot of marks there)

The rate of change of momentum of a body is proportional to the resultant force acting on the body and is in the same direction.

F [proportional symbol] ma
F=kma
but 1newton gives a 1kg mass an acceleration of 1ms^-1
therefore 1=(k)(1)(1), k=1

F=ma


EDIT: too slow

Jonathan

A tuning forks second harmonic is 512Hz.
What is its fundamental frequency?
What is its second overtone?

JC 2K3

I'm rusty on this but...

256Hz and 768Hz?

Nehpets

fundemental freq is 256Hz and it's second overtone is 768Hz(think it's Hz??)

EDIT: too slow

What is the SI unit of temperature? Kelvin or Celcius?

A 600 W heater raised the temperature of 2.5 kg of water from 12 C to 90 C in 22.7 minutes. Calculate the specific heat capacity of the water.

carlowboy

Nehpets wrote:

fundemental freq is 256Hz and it's second overtone is 768Hz(think it's Hz??)

EDIT: too slow

What is the SI unit of temperature? Kelvin or Celcius?

A 600 W heater raised the temperature of 2.5 kg of water from 12 C to 90 C in 22.7 minutes. Calculate the specific heat capacity of the water.

Kelvin


Re that question, I keep getting 2.259 X10^-3 even though the answer should be 4320. Did you make those figures up yourself?



Define magnetic flux density (has never come up in the exam papers btw)

madnirvana

Nehpets wrote:

fundemental freq is 256Hz and it's second overtone is 768Hz(think it's Hz??)

EDIT: too slow

What is the SI unit of temperature? Kelvin or Celcius?

A 600 W heater raised the temperature of 2.5 kg of water from 12 C to 90 C in 22.7 minutes. Calculate the specific heat capacity of the water.

Kelvin


P=600 E=? T= 22.7 * 60 = 1362 seconds.

P=E/t

600=E/1362 E= 817200


Q=MwCw(Change in Temp)

817200= 2.5 (Cw) ( 90-12 )

10476.9 = 2.5 Cw

Cw= 4190 Ans

carlowboy

S*it the bed I made one of the stupidest mistakes ever. I really should try to work these out with a pen first!

madnirvana

carlowboy wrote:

Kelvin


Re that question, I keep getting 2.259 X10^-3 even though the answer should be 4320. Did you make those figures up yourself?



Define magnetic flux density (has never come up in the exam papers btw)

F=IlB => B= F/IL

I = Current L= length of conductor B= Megnatic Flux density
F= Force on conductor you can write this for it by the way. No need for definition.


Or I = BA I= Magnetic Flux A= Area B= M.F density

carlowboy

sure? thought you needed to refer to right angles and all that (can't think of it off hand)

madnirvana

carlowboy wrote:

sure? thought you needed to refer to right angles and all that (can't think of it off hand)

yeah cuz in marking schemes they only write the formula and the units.
and what each letter means...

carlowboy

I think it may be an exception though as the definition of it is a lot more precise than any formulae and as I've posted before, there are no marking schemes for it.....yet...

charlie1234

What is the relation between the resistivity and the length of a wire?

Name 3 precautions to be taken when measuring the acceleration due to gravity of an object.

eZe^

carlowboy wrote:

sure? thought you needed to refer to right angles and all that (can't think of it off hand)

For the lc course the problems are always perpendicular, therefore the sin90 = 1, so you dont need to mention angles.

JC 2K3

^That's not true....

In some problems you are required to relsolve the perpendicular componant of a non perpendicular vector to calculate a problem involving magnetic flux density, force and current.

eZe^

JC 2K3 wrote:

^That's not true....

In some problems you are required to relsolve the perpendicular componant of a non perpendicular vector to calculate a problem involving magnetic flux density, force and current.

Show me a LC question with it and ill retract my statement!

madnirvana

carlowboy wrote:

I think it may be an exception though as the definition of it is a lot more precise than any formulae and as I've posted before, there are no marking schemes for it.....yet...

no but the other questions i hav read they say ''define''..
but in marking schemes they just write the formula and explain it.

E92

JC 2K3 wrote:

^That's not true....

In some problems you are required to relsolve the perpendicular componant of a non perpendicular vector to calculate a problem involving magnetic flux density, force and current.

I thought that they had to be _|_ as well? How do you do it otherwise?


Thanks for the help lads.

Explain the difference between Pair Production and Pair Annihalation, plus what are the equations for these?

ninebeanrows

E92 wrote:

I thought that they had to be _|_ as well? How do you do it otherwise?


Thanks for the help lads.

Explain the difference between Pair Production and Pair Annihalation, plus what are the equations for these?

Pair annihilation is when a electron and positron collide to form two gamma rays which emit off at 90 degree angles to collision.

e+ + e- = 2 gamma rays

Pair production is when a photon hits a nucleus of an atom and an electron and positron are formed.

2 gamma rays

---

> e+ + e-

??

JC 2K3

eZe^ wrote:

Show me a LC question with it and ill retract my statement!

Do you have Real World Physics? Look at page 303.

I doubt they'd tell you how to do it were it not on the syllabus...

E92

thanks

JC 2K3

I think pair production and annihilation refer to any particle and its respective antiparticle, not just electrons and positrons...

carlowboy

isn't it

one gamma ray-> e^1 + e^-1?

Help me if I'm wrong

JC, Its ok to use it as an example though?

JC 2K3

Yeah, wikipedia seems to say that pair production generlly refers to positrons and electrons anyway.

Limerick Dude

JC 2K3 wrote:

Yeah, wikipedia seems to say that pair production generlly refers to positrons and electrons anyway.

Im sorry but im finding particle physics a bit difficult, could you define pair production and annilhation in words and then the formula for both? Cheers.

carlowboy

Basically anti-particle and the particle have the same mass and exactly opposite charges ie. if it was one, the other's would be minus one. When they come together, they basically destroy each other, which gives off energy and the charges cancel each other out. All that's left from the energy given off are two photons that travel in opposite directions with no charge.

That help?

JC 2K3

Pair production:

What happens: A photon from a gamma ray hits a nucleus and the energy of that photon is converted into an electron and a positron. The move away from each other at right angles to each other as you see in this diagram.

Why it happens: Remember the formulae E = hf and E = mc^2? The first one means the energy of photons in electromagnetic radiation depends on the frequency of that radiation. Gamma rays have a relatively high frequency and therefore a high amount of energy, enough energy, in fact, to equate to the masses of a positron and an electron times the speed of light squared(E=mc^2). You don't have to know why it happens when the ray hits a nucleus(it's to do with electromagnetic force in the nucleus AFAIK), but basically the gamma ray has enough energy to be converted into a positron and an electron, and that's what happens. They move away at right angles to conserve the momentum of the photon and they conserve charge since the sum of their charges is zero.

Y -> e+ + e- + Ek

Pair Annihilation:

The opposite of above, except 2 photons with less energy are produced this time. Two have to be produced to conserve momentum.

e+ + e- -> 2Y + Ek

ZorbaTehZ

There can also be other pairs produced too along with the photons, for example a negative/positive pion pair.

I don't see a question, so:

Q: Myopia is "short-sightedness". What is the the term for "long-sightedness" and which type of lens is used to correct each condition?

EDIT: Typo.

JC 2K3

You correct short sightedness with a diverging lens, long sightedness with a converging lens, and I've no idea what the term for long sightedness is.