# Physics - The Nuclear Atom

> Source: https://ollybritton.com/notes/a-level/physics/topics/nuclear-atom/ · Updated: 2022-01-20 · Tags: school, physics, particle-physics

## Flashcards
### 2022-01-20
##### What did J. J. Thomson discover in 1897??
The electron.

##### What model did J. J. Thomson propose for the atom??
The plum pudding model.

##### What is the plum pudding model??
The idea that an atom contains negative electrons embedded in a uniform sea of positive charge.

##### What is the one-sentence summary of the alpha-scattering experiment??
Fire alpha particles at a thin gold film and see where the alpha particles are deflected to using a microscope.

##### What was special about the screen surrounding the alpha-scattering experiment setup??
It was fluorescent and would light up when a particle hit it.

##### What is an alpha particle??
A helium nucleus, two protons and two neutrons.

##### What is the charge of an alpha particle in terms of $e$??
$$
+2e
$$

##### How was the microscope set up in the alpha-scattering experiment??
On a swivel so it could see all around the fluorescent screen.

##### What three observations came about because of the alpha-scattering experiment??
* Most alpha particles passed straight through
* 1 in 2000 particles were scattered
* 1 in 10,000 particles were deflected over an angle of 90 degrees

##### What did the observation that most alpha particles passed through the gold foil in the alpha-scattering experiment mean??
That most of an atom is empty space with empty space concentrated in a small region.

##### What did the observation that 1 in 10,000 alpha particles were deflected at angles greater than 90 degrees mean??
That the nucleus of an atom has a positive charge.

##### What is the charge of a nucleus in terms of its atomic number $Z$ and the elementary charge $e$??
$$
+Ze
$$

##### What word other than "collide" should you use when describing the alpha-scattering experiment??
Deflected, as they never actually touch.

### 2022-01-27
##### How did Rutherford calculate an estimate for the size of the nucleus??
Assumed that all the kinetic energy in an alpha particle is transferred to electric potential.

##### What two things would you equate to work out an estimate for the size of a nucleus??
Kinetic energy and electric potential energy.

##### Was Rutherford's estimate for the size of a nucleus an overestimate or underestimate??
An overestimate.

##### What is the approximate size of an atom??
$$
10^{-10} \text{m}
$$

##### What is the approximate size of a nucleus??
$$
10^{-15} \text{m}
$$

##### How many orders of magnitude smaller is a nucleus than an atom??
$$
5
$$

##### Which is bigger: the nucleon number or the proton number??
The nucleon number.

##### What is another word for the nucleon number??
Atomic mass.

##### What is another word for atomic mass??
Nucleon number.

##### What is another word for the proton number??
Atomic number.

##### What is another word for atomic number??
Proton number.

##### What's the difference between atomic mass and atomic number??
Atomic mass is the total amount of things in the nucleus, whereas the atomic number is just the number of protons.

##### How would you work out the number of neutrons in an atom given the proton number and the nucleon number??
$$
\text{nucleon number} - \text{proton number}
$$

##### What determines an element??
The number of protons it has.

##### What's an isotope??
Atoms with the same number of protons but a different number of neutrons.

##### What is $1 \text{u}$??
One atomic mass unit.

##### Where does the definition for $1 \text{u} = 1.661 \times 10^{-27}$ come from??
It is $1/12$ the mass of a nucleus of Carbon-12.

##### Which is heavier: a proton or a neutron??
A neutron.

##### What is the equation for the approximate radius of a nucleus??
$$
R = r_0 \times A^{1/3}
$$

##### In the equation $$R = r_0 \times A^{1/3}$$ what is the value of $r_0$??
$$
1.2 \text{fm} = 1.2 \times 10^{-15}
$$

##### What does $A$ represent in the equation $$R = r_0 \times A^{1/3}$$??
The nucleon number, i.e. the number of atoms in the nucleus.

### 2022-01-31
##### Why is the density of a nucleus independent from the number of nucleons it contains??
Because the value of $A$ cancels out in its equation.

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