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Physics: A Bitch of an exam

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2

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    #32
    Cokehead Mother
    Closed Accounts Posts: 773 ✭✭✭Cokehead Mother


    A body immersed in a liquid experiences an uptrust equal to the weight of the liquid displaced.

    How can an accelerating particle have a constant speed?


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    #33
    kaki
    Registered Users Posts: 674 ✭✭✭kaki


    If it's undergoing circular motion, it will always experience an accelerating force towards the centre, yet it's instanteous velocity will remain constant.

    Describe and explain the shape of an I/V graph for a vacuum.


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    #34
    acidstorm
    Closed Accounts Posts: 41 ✭acidstorm


    Cokehead Mother wrote: »
    A body immersed in a liquid experiences an uptrust equal to the weight of the liquid displaced.

    How can an accelerating particle have a constant speed?

    When the body moves in a circle the magnitude of the velocity (speed) is the same but the direction is changing.

    An experiment to explain the photoelectric effect?


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    #35
    kaki
    Registered Users Posts: 674 ✭✭✭kaki


    Experiment: Charge an electroscope by induction positively by induction, place on top of a gold leaf electroscope, allow UV light to fall on the zinc sample, and watch as the gold leaves converge...

    I won't ask another question yet


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    #36
    Cokehead Mother
    Closed Accounts Posts: 773 ✭✭✭Cokehead Mother


    I've never come across the I-V graph of a vacuum before so this may all be very wrong but...

    Vaccum's are completely empty so there's no charged particles and hence they're total insulators. So I is just going to be 0... because V = IR and R = V/I then I being 0 would make R tend towards infinity which is what a 100% insulator type thing would have? So basically it's just going to be a straight line along the x-axis... I think? :confused:

    Distinguish between intrinsic and extrinsic semiconductors.


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    #37
    kaki
    Registered Users Posts: 674 ✭✭✭kaki


    Re the graph for a vacuum: You'd think it's 0 alright, but if the cathode gets hot enough, thermionic emission occurs, and electrons travel across the tube. As the p.d. increases, so does the current, until all possible electrons have been emitted, and it levels off.

    Intrinsic conduction = Conduction in a pure semiconductor due to electrons moving from negative to positive, and an equal number of holes moving in the opposite direction. Extrinsic conduction = the increased conduction of a semi-conductor due to doping (addition of controlled amounts of impurities).

    Q: Explain magnetic variation


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    #38
    kaki
    Registered Users Posts: 674 ✭✭✭kaki


    Crappy illustration of IV graph for vacuum
    ivcd8.png


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    #39
    cartman444
    Closed Accounts Posts: 125 ✭✭cartman444


    hey i just cant seem to get my head round how a rocket works!lol

    it says in my book the burning gas has a very high velocity so a large momentum and therefore the rocket has an equal and opposite momentum in the other direction. but if the momentii() are equal then in opposite directions does that not mean they cancel each other out and it shouldnt move!!


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    #40
    acidstorm
    Closed Accounts Posts: 41 ✭acidstorm


    cartman444 wrote: »
    hey i just cant seem to get my head round how a rocket works!lol

    it says in my book the burning gas has a very high velocity so a large momentum and therefore the rocket has an equal and opposite momentum in the other direction. but if the momentii() are equal then in opposite directions does that not mean they cancel each other out and it shouldnt move!!

    I think you forgot Newton's third law--> To every action, there is an equal but opposite reaction. So If the gas is being pushed out, the gas molecules kinda push the rocket the other way.

    Think of this--> When you stand on the floor, there is a force pushing against your feet and obviously, a force pushing down on the floor , hence your knees start to hurt if you stand for too long. the force is equal to your weight, thats why you dont fly off the surface of the earth, however, a rocket on the launchpad for example blasts out so much more force than its own weight, hence it moves forward.

    Hope this helps


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    #41
    acidstorm
    Closed Accounts Posts: 41 ✭acidstorm


    kaki wrote: »
    Q: Explain magnetic variation
    This is the difference between the geographical north and the magnetic north. I actually know this as angle of declination and I had to confirm that they were the same thing before I posted


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    #42
    Cokehead Mother
    Closed Accounts Posts: 773 ✭✭✭Cokehead Mother


    Nobody asked a question soo...

    what is the principle on which the definition of the ampere is based and briefly outline an experiment to demonstrate this.


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    #43
    Patrickisperfec
    Closed Accounts Posts: 121 ✭✭Patrickisperfec


    when 2 wires are 1 metre apart and there is a current of 1Amp flowing through them, there should be a force 1.6x10^16 (I think)N against each other.


    Not sure about the exp.

    Name 2 Mesons


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    #44
    cartman444
    Closed Accounts Posts: 125 ✭✭cartman444


    acidstorm wrote: »
    I think you forgot Newton's third law--> To every action, there is an equal but opposite reaction. So If the gas is being pushed out, the gas molecules kinda push the rocket the other way.

    Think of this--> When you stand on the floor, there is a force pushing against your feet and obviously, a force pushing down on the floor , hence your knees start to hurt if you stand for too long. the force is equal to your weight, thats why you dont fly off the surface of the earth, however, a rocket on the launchpad for example blasts out so much more force than its own weight, hence it moves forward.

    Hope this helps[/QUOTE

    CHEERS!!!! I think I understand now!


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    #45
    acidstorm
    Closed Accounts Posts: 41 ✭acidstorm


    Cokehead Mother wrote: »
    Nobody asked a question soo...

    what is the principle on which the definition of the ampere is based and briefly outline an experiment to demonstrate this.

    is that the experiment with the aluminium foil and a block where the two wires have current flowing in opposite directions. the wires move away from each other. I hope no one has answered it already

    How is the ice dried in the latent heat of fusion experiment..


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    #46
    salman85
    Closed Accounts Posts: 135 ✭✭salman85


    acidstorm wrote: »
    How is the ice dried in the latent heat of fusion experiment..

    crushed using pestle + mortar, dried using a tissue

    explain how momentum is conserved in beta decay


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    #47
    acidstorm
    Closed Accounts Posts: 41 ✭acidstorm


    salman85 wrote: »
    crushed using pestle + mortar, dried using a tissue

    explain how momentum is conserved in beta decay

    By the introduction of the neutrino?

    What are cathode rays


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    #48
    cartman444
    Closed Accounts Posts: 125 ✭✭cartman444


    cathode rays are rays/streams of high speed electrons.

    1.they can be deflected by magnetic and electric fields.
    2.they have a negative charge.
    3.they are used in tv's to produced images.

    how does they geiger/muller tube/counter work?


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    #49
    acidstorm
    Closed Accounts Posts: 41 ✭acidstorm


    cartman444 wrote: »
    how does they geiger/muller tube/counter work?

    They have an anode and a cathode, and connected to a high voltage source. They contain gases at low pressure (Argon esp) When radiation goes into the tube, It ionises the gases, and thus allows the electrons move to the anode, the resulting current can then be connected to a speaker or an LCD to show the count. I personally think of it as electrolysis of a gas lol

    Oh and by the way, I think they got it wrong on the No 5 question in this quiz -->http://www.scoilnet.ie/Quiz.aspx?id=698
    Who discovered X Rays


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    #50
    blueepurple
    Closed Accounts Posts: 8 ✭blueepurple


    rontgen i think.

    who invented the cloud chamber?


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    #51
    salman85
    Closed Accounts Posts: 135 ✭✭salman85


    blueepurple wrote: »
    who invented the cloud chamber?

    not on the course.


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    #52
    Peleus
    Registered Users Posts: 784 ✭✭✭Peleus


    Patrickisperfec wrote: »
    Name 2 Mesons

    nobody answered this so:

    Pion (π) and the kaon (K)


    What is the thermometric property of a thermocouple? Give two other examples of thermometric properties.


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    #53
    salman85
    Closed Accounts Posts: 135 ✭✭salman85


    Peleus wrote: »
    nobody answered this so:

    Pion (π) and the kaon (K)


    What is the thermometric property of a thermocouple? Give two other examples of thermometric properties.

    emf

    liquids=mercuery and alcohol
    crystals = strips which change colour corresponding to temprature range

    who invented the first circular particle acceleator, what did it consist of?


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    #54
    cartman444
    Closed Accounts Posts: 125 ✭✭cartman444


    salman85 wrote: »
    emf

    liquids=mercuery and alcohol
    crystals = strips which change colour corresponding to temprature range

    who invented the first circular particle acceleator, what did it consist of?

    ??????

    em does anyone know why zinc of 4eV is unsuitable for use in photocell??(mock q!)


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    #55
    Peleus
    Registered Users Posts: 784 ✭✭✭Peleus


    cartman444 wrote: »
    ??????

    em does anyone know why zinc of 4eV is unsuitable for use in photocell??(mock q!)

    zinc of 4eV ??? don't know what the electron volts signify there. maybe the work function of it. But if is says it unsuitable then maybe the work function is too high for the light that is shining on the cell.

    i think the photocell is for visable light and visable light is not high enough frequency to knock elctrons off a zinc plate. Zinc needs UV light (high freq).
    salman85 wrote: »
    who invented the first circular particle acceleator, what did it consist of?

    no idea who invented it but it was a linear particle accelerator and accelerated particles using high tension volatages. I think the cockroft and walton experiment was the first particle accelerator. so yea, cockroft and walton invented it!


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    #56
    salman85
    Closed Accounts Posts: 135 ✭✭salman85


    cartman444 wrote: »
    ??????

    em does anyone know why zinc of 4eV is unsuitable for use in photocell??(mock q!)

    not on the course ... its a mock question dunno if we had it on our mock but our mock was the most retarded mock ever, our teacher scraped all 18 mocks and gave us another one on a later date


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    #57
    Decerto
    Registered Users Posts: 309 ✭✭Decerto


    what conditions need to be present for motion to be classed as SHM and when does this apply to a simple compound pendulum


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    #58
    cd17
    Closed Accounts Posts: 1 ✭cd17


    anyone know what is the reason for using glycerol instead of water in the experiment to measure the variation of resistance of a thermistor/metal wire...?


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    #59
    Peleus
    Registered Users Posts: 784 ✭✭✭Peleus


    cd17 wrote: »
    anyone know what is the reason for using glycerol instead of water in the experiment to measure the variation of resistance of a thermistor/metal wire...?

    water has a high specific heat capacity so it takes alot of energy to raise the temp of i kg of water by one degree. glycerol has a low specific heat capacity so it takes low ammounts of heat to raise its temp. so gylcerol will heat faster and give a better and more accurate result. something like that.
    Decerto wrote: »
    what conditions need to be present for motion to be classed as SHM and when does this apply to a simple compound pendulum

    a body is moving in SHM if it's acceleration is directly proportional to it's displacement from a fixed point on it's path and
    it is always accelerating towards that point.

    a simple compund pendulum will execute SHM for small angles (< 5degrees)

    describe briefly how a photocell works and give two applications of it.


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    #60
    Decerto
    Registered Users Posts: 309 ✭✭Decerto


    light shines on the cathode, releasing electrons by photoelectric effect, these are then attracted to the anode, this creates a current in the circuit

    It is used in burgular and smoke alarms and in automatic doors

    Explain how a photocopier works


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    #61
    Peleus
    Registered Users Posts: 784 ✭✭✭Peleus


    Decerto wrote: »
    light shines on the cathode, releasing electrons by photoelectric effect, these are then attracted to the anode, this creates a current in the circuit

    It is used in burgular and smoke alarms and in automatic doors

    Explain how a photocopier works

    i think i know this one. using lazers a static charge is induced on certain points on the page. the places on the page that need to have text on them are charged. The ink particles and attracted to these points due to static electricity and they stick to them. thats basically the jist of it.


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