PHY6 Questions Watch

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qqqwwweee
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What are the similarities and differences between electric and gravitational fields?

I try to list some below:
similarities
  • field and force obey inverse square law
  • act at all distances including infinity
  • force proportional to both properties of objects
  • field due to the object proportional to its property


differences
  • gravitational is always attractive, but electric can be repulsive as well
  • gravitational due to mass, electric due to charge
  • Electrostatic shielding is possible but gravitational (i am not sure about ths)


what else?
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Nylex
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There isn't shielding from gravitational fields. Another difference is that electric fields are a lot stronger than gravitational ones.
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The Albatross
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this is what i have in my notes:

SIMILARITIES
  • Gravitational fields affect all masses, electric fields affect all charges
  • Gravitational forces are proportional to mass. elecrtic forces are proportional to charge.
  • Gravitational field strength is force per unit mass, Electric field strength force per unit charge.
  • Gravitational Equipotentials: lines of equal gravitational energy. Electrical equipotentials: lines of equal electrical energy.
  • Forces between point masses obey inverse square law, as do the forces between point charges. (similarity of Newton's/Coulomb's laws)
  • Point masses and spherical masses produce radial fields. Point and spherical charges produce radial fields.
  • Near to a spherical body, there is a uniform gravitaional field. Near to a spherical charge there is a uniform parallel field.
DIFFERENCES
  • There is also a uniform parallel field between two plates. this cannot happen with gravity.
  • All masses attract. there are no repulsive forces with gravity. Electric fields can have repulsive and attractive forces. Like charges repel, unlike charges attract.
  • There is nothing you can do to shield a mass from the gravitational effect of other masses. You can shield a charge so that it has no effect on another charge - by putting a metal container connectted to earth around it.
there, i hope this is useful!
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S1M
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(Original post by scarlet ibis)
SIMILARITIES
  • Gravitational fields affect all masses, electric fields affect all charges
  • Gravitational forces are proportional to mass. elecrtic forces are proportional to charge.
  • Gravitational field strength is force per unit mass, Electric field strength force per unit charge.
  • Gravitational Equipotentials: lines of equal gravitational energy. Electrical equipotentials: lines of equal electrical energy.
thanks... but these seem like differences to me...
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qqqwwweee
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thanks all!

I ve got others questions.

Is the potential of a Van de Graaff generator positive or negative?
How does a Van de Graaff produce particles of high energy?

What are fixed target experiments and colliding beam experiments?

How does a drift chamber work? Is it similar to a spark chamber?
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The Albatross
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(Original post by S1M)
thanks... but these seem like differences to me...
they are only different in that gravitaional forces affect masses and electric forces affect charges. they way in which they affect them is the same.
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The Albatross
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(Original post by keisiuho)
thanks all!

I ve got others questions.

Is the potential of a Van de Graaff generator positive or negative?
How does a Van de Graaff produce particles of high energy?

What are fixed target experiments and colliding beam experiments?

How does a drift chamber work? Is it similar to a spark chamber?
ooh questions to answer, yay!

See the attatched diagram of a Van de graaf accelerator. its quite good i think. the belt removes negative charge from the sphere, causing it to become highy positively charged.
an ion source, at the same potential as the dome, produces ions which enter a column of cylidrical electrodes. each one is at a lower potential than the one above, so the ions are accellerated by the electric fields in the gaps between the electrodes.

Fixed target experiments are ones where the beam of particles (from an accelerator) collides with a stationary target. because of conservation of momentum, the total momentum of the particles after the collision must be equal to that of the incident particle. therefore most of the energy of the incident particle can't be used to create new particles.
In colliding beam experiments, beams of particles collide with their antiparticles, moving in the opposite direction at the same speed. the momentum after is zero. so all the energy is used to create new particles. however, the disadvantage is that the collision rates are lower.

will post about spark chambers in a minute!
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The Albatross
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not quite sure what you mean by drift chambers, keisiuho.:confused:

'drift tube accelerator' is another name for a linear accelerator, which is not at all similar to a spark chamber.

but cloud chambers and bubble chambers are very similar to spark chambers in that they are all used to detect beams of charged particles.

cloud chambers are filled with supersaturated alcohol vapour, which will condense on ionised atoms in preference to neutral atoms. the beam of charged particles ionises the atoms, so the path of the beam shows up as a series of drops of condensation.
bubble chambers work in a similar way. the chamber contains superheated liquid hydrogen (at a higher temp that it would normally be as a liquid) the ions produced by the passage of charged particles act as nucleating site on which the bubbles form. the path of a beam shows up at a trail of bubbles, which can be photographed.
spark chambers consist of a wire mesh anode at a high potential in comparison to a nearby metal plate. when a charged particle passes between them, the air becomes conducting, and a spark jumps across the gap, which shows the presence of the particle. a beam of charged particles would show up as a trail of sparks.

phew!
well i hope this answers your questions!
writing these actually helps me loads with my revision, so if anyone has any more questions...
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qqqwwweee
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(Original post by scarlet ibis)
not quite sure what you mean by drift chambers, keisiuho.:confused:
I found this term in the specification along with spark chambers.
So they may be the same thing
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[_Z_]
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Can someone pls find out what a drift chamber is?.....
its mentioned along with spark, cloud and bubble chambers in the edexcel syllabus .....no idea what it is!! :confused:
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[_Z_]
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Does ne one have the jan 2004 phy 6 paper?? If so pls post it... of email it to me...
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The Albatross
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(Original post by [_Z_])
Can someone pls find out what a drift chamber is?.....
its mentioned along with spark, cloud and bubble chambers in the edexcel syllabus .....no idea what it is!! :confused:
i haven't got anything in my notes about it.
here's something about them on a website
http://www.nobel.se/physics/educatio...2/chamber.html
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