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Medical Physics > Dipole > Flashcards

Dipole Flashcards

1
Q

What is an electric field defined by?

A

1) electric field strength
2) electric potential

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2
Q

What is the symbol for the “electric field strength”?

A

E with an arrow on top

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3
Q

What is the equation for calculating the electric field strength?

A

E (arrow) = F (arrow) / q

E (arrow)- electric field strength
F (arrow)- net electric force
q- magnitude (of the test charge)

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4
Q

What do fields do? What does that cause?

A

they superimpose each other, forming a single net field.

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5
Q

What does the vector specify? What is a vector?

A

The vector specifies the magnitude of the net field at any point.
It is the vector sum of the values of fields due to each individual source.

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6
Q

What is Coulombs law? What does it explain?

A

Coulomb’s law describes the strength of the electrostatic force (attraction or repulsion) between two charged objects.

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7
Q

What is the Coulombs law equation?

A

E= k*q / Er^2

E- electric field
k- permitivity constant
q- charge
E-
r- radius

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8
Q

What is the symbol for potential?

A

φ
o with a vertical line going across it.

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9
Q

What is the electric potential?

A

The amount of work needed to move a unit charge from a low potential region to a high potential region against an electric field.

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10
Q

What is the equation for electric potential?

A

φ=W/q

φ- electric potential
W- work
q- charge

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11
Q

What does q stand for?

A

charge

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12
Q

What does W stand for

A

work

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13
Q

What is the equation for the potential φ of charge q?

A

φ = kq / (er)

φ- potential
k- constant
q- charge
e- emittance
r- radius

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14
Q

How to express the electric field strength as a ratio in regards to potential difference?

A

E (arrow) = -dφ / dr
E (arrow) = - gradient φ

E (arrow) - electric field strength
φ - potential

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15
Q

What does the minus sign represent in the ratio of the gradient of potential to the electric field strength?

A

the field strength direction coincides with a decrease in potential.

field strength and potential are inversely correlated.

NOTE: the greater the field strength (closer together), the smaller the electric potential (less work had to be done to carry the “ball” up).

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16
Q

What does a dipole consist of?

A
  • two charges
  • equal magnitude
  • opposite charge
  • held at a fixed distance
  • make up a single unit
17
Q

What is magnitude?

A

The absolute or relative direction or size in which an object moves in the sense of motion.

18
Q

What constitutes to the dipole moment?

A

the product of the charges or their seperation.

19
Q

What is the equation for the dipole moment?

A

p (arrow) = (q*1) (arrow)

p- vector quantity (pointing fro the negative charge to the positive charge)

20
Q

What are the units of the dipole moment?

A

C×m

21
Q

Why do some molecules have a dipole moment?

A

Because they exhibit a charge seperation.

22
Q

Why does water have an electric dipole moment?

A

Because the electrons in a water molecule spend most of their time in the proximity of oxygen.

23
Q

Why does a molecule develop a dipole moment?

A

Random fluctuations in the configuration of a molecule lead to charge separation causing a molecule to develop a dipole moment.

24
Q

What does a dipole moment give rise to? What is the further effect?

A

Dipole moments give rise to electric fields which cause charge separation in nearby molecules, giving them a dipole moment as well.

25
Q

What are induced dipoles?

A

The dipole molecules which were formed due to a surrounding molecule being a dipole (having random fluctuations in configuration) and generating an electric field.

26
Q

What is the equation used to calculate the potential of the dipole electric field?

A

φ = k * p * cos⊜ / (e*r^2)

φ- potential of the dipole
k- contant
p- vector quantity
⊜- angle between teh dipole axis and the line seperating the given point
e- emmitence
r- radius

27
Q

How is the dipole model useful?

A

It is useful in biomedical descriptions of electric fields, generated by single cells and electrograms.

28
Q

How can one measure the dipole effect?

A

Using a plate filled with wet sand, a galvanometer, a DC source, and two point-like electrodes.

29
Q

What is the source of the electric field in the wet-sand box procedure?

A

the DC source

30
Q

Which direction do electric field signs travel?

A

from the positive pole to the negative pole.

31
Q

What does the charge trace coincide with?

A

The charge trace coincides with the electric field lines (As electric charges flow along the lines of electric fields).

32
Q

How can the sand bath potential difference be detected?

A

using a galvanometer

33
Q

When is no current detected?

A

when there is zero magnitude.

34
Q

What is the equation for calculating the electric field strength between electrodes?

A

E = -∆φ / ∆s

E- electric field strength
φ- potential (estimated by the galvanometer)
s- separation of arms

35
Q

What is ∆φ in other words?

A

∆φ = I * R

∆φ- electric potential
I - current
R- resistivity (ohms)

36
Q

What is the principal method of investigating the dipole moment?

A

1) The sand in a plate is moistened (not too much), then the surface is smoothed and pressed.
2) connect the DC to the poles L1 and L2.
3) Divide the line between the poles into
eight equidistant intervals.
4) Put one arm of the galvanometer to
point 1, another - some distance apart in such a way such that the pointer would be at its initial (zero deflection) place (change in potential=0).
Draw a line connecting the points (all these points have the same potential).
5) Repeat the analogous operation for points 2,….,7.
6) Calculate the electric field strength between electrodes using the
formula:

E = -∆φ / ∆s

Medical Physics (8 decks)

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