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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date: 2022-01-20 19:31
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title: Physics - The Nuclear Atom