Physics Pop Quiz

nedward

Gravitational : Acts upon all particles
Strong nuclear : Strongest of four forces.

Define an electric field.

ZorbaTehZ

An Electric Field is that area around a charged particle, in which another charged particle would experience a force.

Q: Copper electrodes in a copper sulphate solution, obey Ohm's Law very rigidly. What is the effect of replacing the copper electrodes with platinum electrodes (or another appropriate inert element)?

EDIT: lol, the proper way I should have put it is: What does the graph of V against I look like for inert electrodes in a copper sulphate solution?

carlowboy

Is that the inactice electrodes? Is it that there is a greater emf between the electrodes that has to be overcome. I'm not great on the electricity.....and they don't obey ohm's law.


What is the difference for a capacitor when in an ac circuit as opposed to a DC circuit?

nedward

The line doesn't come from the origin, but bursts forth from the X-axis, ie a certain voltage needs to be put across the electrodes before a current will flow.

carlowboy

nedward wrote:

The line doesn't come from the origin, but bursts forth from the X-axis, ie a certain voltage needs to be put across the electrodes before a current will flow.

So my answer is ok then?

nedward

carlowboy wrote:

So my answer is ok then?

Ugh, didn't see your (pitiful excuse for an) answer. Which is right, yes. :cool:

EDIT A capacitor will conduct current in an ac circuit, but will not conduct in a d.c.

Define refractive index of a medium.

ZorbaTehZ

nedward wrote:

The line doesn't come from the origin, but bursts forth from the X-axis, ie a certain voltage needs to be put across the electrodes before a current will flow.

Bingo. You could make reference to the creation of oxygen, hence a back EMF if you wanted to be OCD about it.

Depends on the circuit, but in terms of a typical LC question it is as though it was not there ie charge builds up on one side, and then when the current changes direction the charge tends to the other side of the graph ad nauseum etc.

When in a DC current, it gains charge until there is no PD between that plate, and the side of the battery it is connected to ie +-6v etc.

Q: Explain how an RCD works.

spudington16

Electricity is just plain unpleasant... I hope not to have to go into too much detail on it tomorrow, trully...

tolosenc

An RCD measures the difference in current between live and neutral, and if it is greater than 30mA it trips and cuts the circuit.

Refractive index is a measure of how much slower the speed of light is in a medium yadda yadda.

What is the difference in quark composition between Mesons and Baryons?

nedward

An RCD consists of an electromagnet and a bimetallic strip. When the current reaches a preset value (too high), one or other of them will trip and break the circuit.


What is an MCB? Give one advantage of it and give the difference between the live and neutral at which it will trip.

EDIT Dammit, too slow.

nedward

Mesons consist of any one quark and antiquark eg up anti-down.
Baryons consist of any three quarks or any three antiquarks.

See q above.

Limerick Dude

Little help with a question im on......

The activity of a radioactive isotope decays to 1/16th of its original value after 36 years. what is the half life of the isotope?

microbiek

Turnip2000 wrote:

The answer to that question is dont bother your hole with light!!

it will still come up and that derivation hasnt eva cum up

Limerick Dude

Could someone please answer my question and i have another one

What is radioactive decay?

Im not sure is it the spontaneous disentegration of unstable nuclei with the release of energy OR the amount of nuclei of a substance which decays per second

any ideas?

microbiek

Limerick Dude wrote:

Little help with a question im on......

The activity of a radioactive isotope decays to 1/16th of its original value after 36 years. what is the half life of the isotope?

6yrs because it takes 6 halfs to get to 1 36th

genericgoon

Is it not 9 yrs

1/16=1/2^4 Half life formula is 1/2^n there for it takes 4 half lifes to reach a sixteenth and thus its 36/4=9

Turnip2000

Limerick Dude wrote:

Could someone please answer my question and i have another one

What is radioactive decay?

Im not sure is it the spontaneous disentegration of unstable nuclei with the release of energy OR the amount of nuclei of a substance which decays per second

any ideas?

its the spontaneous disintegration......the other one you said is the rate of decay or beqeruel???

Limerick Dude

genericgoon wrote:

Is it not 9 yrs

1/16=1/2^4 Half life formula is 1/2^n there for it takes 4 half lifes to reach a sixteenth and thus its 36/4=9

I think thats correct

Limerick Dude

Turnip2000 wrote:

its the spontaneous disintegration......the other one you said is the rate of decay or beqeruel???

Cheers man!

dudara

9 years is correct.

genericgoon

Being right gives me a warm fuzzy feeling inside.

ninebeanrows

genericgoon wrote:

Being right gives me a warm fuzzy feeling inside.

Can you write out answer more simpldon i tried this q earlier and couldnt for the life of me understand how the answer was 9

thanks

dudara

no probs.

1/16 = 1/(2^4)

So in other words, 4 half-lives have elapsed over the course of the 36 years.

Hence a half-life is 9 years.

genericgoon

Ok basically when given a fraction use this half life formula. 1/2^n where n stands in for the power the 2 is being raised to, n also stands for the amount of half lifes that have happened. For example in this case we got 1/16 now we know from maths that 16=2^4. Therefore n=4. therefore 4 half lifes have taken place. Thus if we divide the time it took 4 halflifes to happen by 4 we get the time taken for one half life. Hope this helps.

ZorbaTehZ

A Miniature Circuit Breaker cuts off the current in a circuit when it is too high for example above 30uA. It is based on an electromagnetic relay switch. It is much slower than an RCD and can be reset.

Q: What is a semiconducter? What is doping?

ZorbaTehZ

Weathercheck wrote:

Can you write out answer more simpldon i tried this q earlier and couldnt for the life of me understand how the answer was 9

thanks

The easiest way to look at it is:

When a radioactive compound decays, that rate of decay is measured in terms of how long it takes for it to decay to half its original size.

T(1/2) = Half-life, is the name for this.
After one T(1/2) we are at half of the original size. After two T(1/2) are at one quarter of the original size, ie one half multiplied by one half.

So clearly you keep multiplying one half times one half times one half ... until you are at the required time.

After 4 T(1/2), or 4 half-lives:

1/2 x 1/2 x 1/2 x 1/2

Which is simply 1/(2^4) = 1/16

So after n half-lives, the sample is at 1/(2^n) of the original size. Easiest way to remember this is to memorize that ie that n[T(1/2)] = 1/(2^n) <-of the original size.

ninebeanrows

Goos Luck to everyone, hopefully it'll be a nice paper with PARTICLE PHYSICS!!!

microbiek

Weathercheck wrote:

Goos Luck to everyone, hopefully it'll be a nice paper with PARTICLE PHYSICS!!!

haha funny u z that

Cokehead Mother

ZorbaTehZ wrote: »

A Miniature Circuit Breaker cuts off the current in a circuit when it is too high for example above 30uA. It is based on an electromagnetic relay switch. It is much slower than an RCD and can be reset.

Q: What is a semiconducter? What is doping?

semi conductor = substances which with outer electrons which aren't free to move but which require little energy to free them for conduction

doping = adding small amounts of another element to a semi conductor to increase its conductivity

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Thought I'd bump this cause the mocks are in 2 weeks and revision can't hurt.

Define capacitance.