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Physics > The Nucleus COPY > Flashcards

The Nucleus COPY Flashcards

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1
Q

What conclusions could be reached from the Rutherford Scattering experiment? (4)

A
  • Most of the atom is empty space
  • The positive charge is concentrated in a very small space
  • The alpha particles that were deflected had to be travelling in a line with the nucleus
  • They were deflected by the electrostatic repusion of the positive nucleus of the positive alpha particle
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2
Q

What was the model of the atom before the Rutherford scattering experiment?

A

The plum pudding model - negative electrons in a thinly spread positive charge

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3
Q

Give a brief explanation of the Rutherford scattering experiment

A

A beam of alpha particles are beamed at a thin sheet of gold. Some alpha particles were deflected.

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4
Q

Why must the gold be thin in the Rutherford scattering experiment?

A

Alpha particles cannot penetrate thick materials

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5
Q

Why must there be a vacuum in the Rutherford scattering experiment?

A

Alpha particles can only travel 2-3 cm in air so may not even reach the foil

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6
Q

Why must the beam of electrons be narroe in the Rutherford scattering experiment?

A

So you can measure the angle of deflection more easily

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7
Q

What happened to most of the alpha particles hitting the foil in Rutherford scattering experiment?

A

They travel through undeflected

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8
Q

When alpha particles are shot at a thin sheet of gold most travel through undeflected, what does this say about the positive charge in a nucleus?

A

It is in a very small and concentrated point

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9
Q

What happened to a few particles in the Rutherford scattering experiment?

A

They were deflected by great angles

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10
Q

What did the Rutherford scattering experiment suggest about the mass and charge of the nucleus?

A
  • Charge is in a small and highly concentrated spot to be able to deflect alpha particles
  • The mass of the nucleus must be great so that the gold atoms are not pushed out of the metal. If the masses were similar they would behave ‘like snooker balls’
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11
Q

How would the results of the Rutherford scattering experiment change is silver foil was used rather than gold. Silver has a lower mass and atomic number than gold.

A

The cherge will be lower and so the alpha particles won’t be deflected as much.

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12
Q

How would the results of the Rutherford scattering experiment eb different if a more energetic alpha particle was used?

A

If the particle is more energetic then it will spend less time near the posirtive charge and so will be deflected less.

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13
Q

Draw the path of an alpha particle hitting a nucleus head on

A
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14
Q

Draw the path of an alpha particle:

a) Hitting the nucleus not head on
b) Hitting the nucleus in the same direction as (a) but with more energy
c) Hitting the nucleus with the same energy as (a), but further away from the nucleus

A
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15
Q

Why do alpha particles slow down as they approach a nucleus?

A

It experiences an electrostatic repulsion which slows it down

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16
Q

Derive the formula for the closest distance of approach of an alpha particle.

A
17
Q

What are the assumptions / inaccuracies made with the formula for the closest distance of approach? (4)

A
  • The alpa partical is assumed to be a point charge (not true)
  • The nucleus does not recoil and gain kinetic energy (which it will do)
  • The scattering is by the electrostatic force and the alpha particles do not get close enough to the nucleus to feel the strong force (they probably will if they have high enough energy)
  • The alpha particles do not penetrate the nucleus and so the true it less than d (d gives too high a value for the radius)
18
Q

Calculate the least distance of approach of an alpha particle to a gold nucleus (Z=79) if the initial kinetic energy of the alpha particle is 8.0x10-13J

A
19
Q

What does the De Broglie wavelength of an electron need to be to have a noticable diffraction pattern?

A

About the same size as the nucleus

20
Q

What is deep inelastic scattering?

A

High energy electrons are fired at protons and are diffracted by the quarks inside the protons

21
Q

How was the diameter of a proton measured?

A
  • Electrons of energy 1000MeV at liquid hydrogen.
  • Hydrogen atoms have a proton as their nucleus
  • From the diffraction pattern produced, the diameter was abled to be measured
22
Q

How does the diffraction pattern of electrons change if the accelerating voltage is increased?

A

The rings become closer

23
Q

What does the diffraction pattern of electrons look like?

A

A circular pattern

24
Q

How do you show the existance of quarks?

A
  • The wavelength of the electrons need to be about the same size of quarks to show a good diffraction pattern
  • To have such a small wavelength, the electrons need a high momentum and thus a high kinetic energy.
  • The fact that there is a diffraction pattern proves quarks.
25
Q

Draw a diagram that shows the method for calculating the size of a nucleus from electon diffraction

A
26
Q

Draw a graph of the intensity of diffracted electrons against diffraction angle

A
27
Q

Why is the estimation of nuclear radius by electron diffraction a more accurate method than alpha scattering ?

A
  • Electrons react with nuclei only through electromagnetic interaction which is better understood than the strong interaction involved in alpha scattering. Electrons are not affected by the strong nuclear force.
  • Electrons penetrate the nucleus but alpha particles do not because because they are repelled by the nucleus before they reach it so electrons give a better value for the radius of the nucleus.
  • There is less recoil of the nucleus when electrons hit it (due to their lower mass). The recoil can complicate calculations.
28
Q

What does the values of the nucleus vary between?

A

About 1 fm - 10 fm

29
Q

Why do values for the radius of the nucleus vary when different methods are used?

A

The nucleus doesn’t have a well defined edge

30
Q

What is the equation for the radius of a nucleus that contains the mass number?

A

R = r0A1/3

R = radius

r0 = constant (different for different methods)

A = mass number

31
Q

Draw the graph of radius against mass number

A
32
Q
  • Draw the graph of radius against (mass number)1/3.
  • What is the gradient?
A
33
Q

Draw the graph of (radius)3 against mass number.

What is the gradient?

A
34
Q

Draw the graph of log(radius) against log(mass number).

What is the gradient? What is the y-intercept?

A
35
Q

If mn is the mass of the nucleon, derive a formula for the density of the nucleus.

A
36
Q

Why do all nuclei have the same density?

A

Density doesn’t depend on the mass number

37
Q
A
  • The density of the nucleus doesn’t depend on the mass number, all nuclei have the same density
  • This means that the separation of nucleons must be constant in all nuclei
38
Q

Determine the radius and the density of a copper-63 nucleus, assuming R = r0A1/3 and taking r0=1.4fm

A
39
Q
A

Physics (15 decks)

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