Define nucleon number .

Nucleon number ( A ) is the total number of protons and neutrons in the nucleus. It is also called the mass number.

Define proton number .

Proton number ( Z ) is the total number of protons in the nucleus. It is also called the atomic number.

An isotope is an atom of the same element with the same number of protons but a different number of neutrons .

How do you calculate the number of neutrons in a nucleus from its nucleon number and proton number?

number of neutrons = nucleon number − proton number

Deuterium and tritium are both isotopes of hydrogen with a proton number of 1. Deuterium has one neutron and tritium has two. What is the nucleon number of each?

Deuterium has a nucleon number of 2 . Tritium has a nucleon number of 3 .

In Chemistry, the nucleon number is referred to as the .......... .

In Chemistry, the nucleon number is referred to as the mass number .

True or False? In a neutral atom, the number of protons is equal to the number of neutrons.

False. In a neutral (uncharged) atom, the number of protons equals the number of electrons , not neutrons. The number of neutrons is found from A − Z .

What is the plum pudding model ?

J.J. Thomson's model of the atom: a sphere of uniformly distributed positive charge , with negatively charged electrons embedded within it, like currants in a pudding.

In the alpha particle scattering experiment, what did it suggest that most alpha particles passed straight through the gold foil undeflected?

That the atom is mainly empty space .

What did the small number of alpha particles deflecting back at angles greater than 90° suggest about the nucleus?

That the nucleus is extremely small and dense , with the atom's mass and positive charge concentrated in one location.

Put these atomic models in chronological order: Rutherford's nuclear model, the quantum mechanical model, Thomson's plum pudding model, Bohr's shell model.

Thomson's plum pudding model (1897) → Rutherford's nuclear model (1909–1911) → Bohr's shell model (1913) → quantum mechanical model (1926)

Bohr improved on Rutherford's model by showing that electrons occupy .......... , at particular distances from the nucleus.

Bohr improved on Rutherford's model by showing that electrons occupy shells (or energy levels), at particular distances from the nucleus.

Which scientist discovered the neutron, and in what year?

James Chadwick discovered the neutron in 1932 .

True or False? The Rutherford scattering experiment showed that atoms are almost entirely solid matter.

False. The experiment showed the opposite: most alpha particles passed straight through the gold foil undeflected, meaning atoms are almost entirely empty space with a tiny, dense nucleus.

Define thermionic emission .

Thermionic emission is the process by which electrons in a heated metal gain enough thermal energy to leave the metal's surface.

How does thermionic emission differ from the photoelectric effect?

In thermionic emission , electrons gain enough energy to leave the metal from thermal energy (heating). In the photoelectric effect , electrons absorb energy from incident photons .

Once electrons are released from a heated metal surface, how are they typically given further energy?

They are accelerated by electric or magnetic fields .

Electrons are emitted from the (negative) .......... , and accelerated toward the (positive) anode.

Electrons are emitted from the (negative) cathode , and accelerated toward the (positive) anode.

True or False? Thermionic emission occurs because electrons absorb energy from photons.

False. Thermionic emission occurs when electrons gain sufficient thermal energy from heating to leave the metal surface. It is the photoelectric effect that involves electrons absorbing energy from photons.

Define linear accelerator (LINAC) .

A particle accelerator that uses electric fields between a series of hollow tubes to accelerate ions in a straight line .

A particle accelerator with two hollow semicircular electrodes ('dees') that uses an electric field (to accelerate ions across the gap) and a magnetic field (to keep ions moving in a spiral path).

Why must the tubes in a LINAC become progressively longer along its length?

The AC supply switches polarity at a constant frequency , and since the ions are speeding up , each tube must be longer so the ion spends the same time under acceleration in each one.

Why is an alternating, rather than direct, potential difference needed to accelerate ions across the gap in a cyclotron?

If the potential difference were not alternated, the ions would only be accelerated in one direction . Alternating it ensures the ions are accelerated every time they cross the gap.

What are the two main physical principles by which particle detectors, such as Geiger-Muller tubes and cloud chambers, detect charged particles?

Ionisation of the surrounding medium and deflection (scattering) of the particle by applied electric fields.

In a cyclotron, the two hollow semicircular electrodes are called .......... .

In a cyclotron, the two hollow semicircular electrodes are called dees .

True or False? A cyclotron uses only a magnetic field to accelerate charged particles.

False. A cyclotron uses both a magnetic field (to curve the ions into a spiral path) and an alternating electric field (in the gap between the dees) to speed them up — the magnetic field alone only changes direction, not speed.

Why does a charged particle moving perpendicular to a uniform magnetic field travel in a circular path?

The magnetic force on it is always perpendicular to its velocity, so it acts as a centripetal force , directed toward the centre of the circular orbit.

How does the radius of a charged particle's path change if the magnetic field strength B is increased, with all else constant?

The radius decreases , since r ∝ 1/ B .

Particles with a larger momentum move in .......... circles, since r ∝ p .

Particles with a larger momentum move in larger circles, since r ∝ p .

True or False? A charged particle with a greater charge moves in a larger circular radius in a magnetic field.

False. Radius is inversely proportional to charge ( r ∝ 1/ q ), so a particle with a greater charge moves in a smaller circle, not a larger one.

What does the radius of curvature of a charged particle's track in a detector indicate?

Its momentum — a larger radius indicates a larger momentum, and a smaller radius indicates a smaller momentum.

Why does the radius of a charged particle's track typically decrease as it spirals inward through a detector?

The particle loses kinetic energy (and therefore momentum) by ionising other particles along its path, so r decreases since r ∝ p .

What does the direction of curvature of a particle's track indicate, and what rule is used to determine it?

The sign of the particle's charge . Fleming's Left Hand Rule is used to determine it.

Define pair creation , as seen in particle tracks.

When a particle track appears to begin 'out of nowhere', splitting into two tracks curving in opposite directions with the same radius — indicating the creation of a particle-antiparticle pair.

Why do particle and antiparticle tracks created in a pair-creation event have the same radius but curve in opposite directions?

They have the same mass (and therefore momentum), giving the same radius, but opposite charges , so the magnetic force — and hence curvature — acts in opposite directions.

Charge, energy and .......... are always conserved in interactions between particles.

Charge, energy and momentum are always conserved in interactions between particles.

True or False? A charged particle track with an increasing radius indicates the particle is losing energy.

False. An increasing radius indicates the particle's momentum (and kinetic energy) is increasing ; a decreasing radius indicates energy loss through ionisation.

Why can high energy electron beams be used to determine the diameter of a nucleon?

Because at high energies, electrons have a de Broglie wavelength comparable to the size of the nucleon, so the scattering pattern produced can be analysed to determine the nucleon's diameter.

Why do electrons give a more precise measurement of nucleon size than alpha particles?

Electrons do not experience the strong nuclear force , so they can get extremely close to nucleons without interacting; alpha particles are made of protons and neutrons, which do interact via the strong force.

The de Broglie wavelength of an electron is .......... proportional to its velocity.

The de Broglie wavelength of an electron is inversely proportional to its velocity.

True or False? Alpha particles give a more precise measurement of nucleon diameter than high energy electrons, because alpha particles are made of protons and neutrons.

False. Electrons do not experience the strong nuclear force and so can approach nucleons without interacting, giving a more precise measurement; alpha particles do interact via the strong force, making them less precise probes.

Define annihilation .

When a particle meets its equivalent antiparticle , both are destroyed and their mass is converted into energy in the form of two gamma-ray photons emitted in opposite directions.

Define pair production .

When a photon interacts with a nucleus (or atom) and its energy is used to create a particle–antiparticle pair .

When a particle and its antiparticle annihilate, their mass is converted into energy in the form of two .......... emitted in opposite directions.

When a particle and its antiparticle annihilate, their mass is converted into energy in the form of two gamma-ray photons emitted in opposite directions.

True or False? A single photon with enough energy can undergo pair production on its own, without a nucleus present.

False. A nearby nucleus (or nucleon) is essential so that both energy and momentum are conserved; a single photon alone cannot produce a particle–antiparticle pair without violating momentum conservation.

How do you convert an energy between joules and electronvolts?

Multiply electronvolts by 1.6 × 10 -19 to get the energy in joules; divide joules by 1.6 × 10 -19 to get the energy in electronvolts.

1 eV is equivalent to .......... J.

1 eV is equivalent to 1.6 × 10 -19 J.

True or False? 1 GeV is a smaller unit of energy than 1 MeV.

False. 1 GeV = 10 9 eV and 1 MeV = 10 6 eV, so 1 GeV is 1000 times larger than 1 MeV.

Define time dilation .

The effect whereby a clock (and hence a particle's measured lifetime) moving at relativistic speed runs slower relative to a stationary observer.

Define length contraction .

The effect whereby the length of an object moving at relativistic speed is measured to be shorter , in the direction of motion, than when at rest.

International A Level (IAL)PhysicsEdexcelFlashcards4. Further Mechanics, Fields & ParticlesExploring the Structure of Matter

Exploring the Structure of Matter (Edexcel International A Level (IAL) Physics): Flashcards

Exam code: YPH11

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FrontNucleon & Proton Number
Define nucleon number.

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Cards in this collection (64)

Define nucleon number.
Nucleon number (A) is the total number of protons and neutrons in the nucleus. It is also called the mass number.
Define proton number.
Proton number (Z) is the total number of protons in the nucleus. It is also called the atomic number.
Define isotope.
An isotope is an atom of the same element with the same number of protons but a different number of neutrons.
How do you calculate the number of neutrons in a nucleus from its nucleon number and proton number?
number of neutrons = nucleon number − proton number
Deuterium and tritium are both isotopes of hydrogen with a proton number of 1. Deuterium has one neutron and tritium has two. What is the nucleon number of each?
Deuterium has a nucleon number of 2. Tritium has a nucleon number of 3.
In Chemistry, the nucleon number is referred to as the ...........
In Chemistry, the nucleon number is referred to as the mass number.
True or False?
In a neutral atom, the number of protons is equal to the number of neutrons.
False.
In a neutral (uncharged) atom, the number of protons equals the number of electrons, not neutrons. The number of neutrons is found from A − Z.
What is the plum pudding model?
J.J. Thomson's model of the atom: a sphere of uniformly distributed positive charge, with negatively charged electrons embedded within it, like currants in a pudding.
In the alpha particle scattering experiment, what did it suggest that most alpha particles passed straight through the gold foil undeflected?
That the atom is mainly empty space.
What did the small number of alpha particles deflecting back at angles greater than 90° suggest about the nucleus?
That the nucleus is extremely small and dense, with the atom's mass and positive charge concentrated in one location.
Put these atomic models in chronological order: Rutherford's nuclear model, the quantum mechanical model, Thomson's plum pudding model, Bohr's shell model.
Thomson's plum pudding model (1897) → Rutherford's nuclear model (1909–1911) → Bohr's shell model (1913) → quantum mechanical model (1926)
Bohr improved on Rutherford's model by showing that electrons occupy .........., at particular distances from the nucleus.
Bohr improved on Rutherford's model by showing that electrons occupy shells (or energy levels), at particular distances from the nucleus.
Which scientist discovered the neutron, and in what year?
James Chadwick discovered the neutron in 1932.
True or False?
The Rutherford scattering experiment showed that atoms are almost entirely solid matter.
False.
The experiment showed the opposite: most alpha particles passed straight through the gold foil undeflected, meaning atoms are almost entirely empty space with a tiny, dense nucleus.
Define thermionic emission.
Thermionic emission is the process by which electrons in a heated metal gain enough thermal energy to leave the metal's surface.
How does thermionic emission differ from the photoelectric effect?
In thermionic emission, electrons gain enough energy to leave the metal from thermal energy (heating). In the photoelectric effect, electrons absorb energy from incident photons.
Once electrons are released from a heated metal surface, how are they typically given further energy?
They are accelerated by electric or magnetic fields.
Electrons are emitted from the (negative) .........., and accelerated toward the (positive) anode.
Electrons are emitted from the (negative) cathode, and accelerated toward the (positive) anode.
An electron is accelerated from rest through a potential difference V. Write an expression for the kinetic energy it gains, in terms of its charge e.
$\frac{1}{2} m v^{2} = e V$
True or False?
Thermionic emission occurs because electrons absorb energy from photons.
False.
Thermionic emission occurs when electrons gain sufficient thermal energy from heating to leave the metal surface. It is the photoelectric effect that involves electrons absorbing energy from photons.
Define linear accelerator (LINAC).
A particle accelerator that uses electric fields between a series of hollow tubes to accelerate ions in a straight line.
Define cyclotron.
A particle accelerator with two hollow semicircular electrodes ('dees') that uses an electric field (to accelerate ions across the gap) and a magnetic field (to keep ions moving in a spiral path).
Why must the tubes in a LINAC become progressively longer along its length?
The AC supply switches polarity at a constant frequency, and since the ions are speeding up, each tube must be longer so the ion spends the same time under acceleration in each one.
Why is an alternating, rather than direct, potential difference needed to accelerate ions across the gap in a cyclotron?
If the potential difference were not alternated, the ions would only be accelerated in one direction. Alternating it ensures the ions are accelerated every time they cross the gap.
What are the two main physical principles by which particle detectors, such as Geiger-Muller tubes and cloud chambers, detect charged particles?
Ionisation of the surrounding medium and deflection (scattering) of the particle by applied electric fields.
In a cyclotron, the two hollow semicircular electrodes are called ...........
In a cyclotron, the two hollow semicircular electrodes are called dees.
True or False?
A cyclotron uses only a magnetic field to accelerate charged particles.
False.
A cyclotron uses both a magnetic field (to curve the ions into a spiral path) and an alternating electric field (in the gap between the dees) to speed them up — the magnetic field alone only changes direction, not speed.
Why does a charged particle moving perpendicular to a uniform magnetic field travel in a circular path?
The magnetic force on it is always perpendicular to its velocity, so it acts as a centripetal force, directed toward the centre of the circular orbit.
State the equation for the radius r of the circular path of a charged particle of mass m, velocity v and charge q in a magnetic field of flux density B.
$r = \frac{m v}{B q}$
Express the radius equation $r = \frac{m v}{B q}$ in terms of the particle's momentum p.
$r = \frac{p}{B q}$
How does the radius of a charged particle's path change if the magnetic field strength B is increased, with all else constant?
The radius decreases, since r ∝ 1/B.
Particles with a larger momentum move in .......... circles, since r ∝ p.
Particles with a larger momentum move in larger circles, since r ∝ p.
True or False?
A charged particle with a greater charge moves in a larger circular radius in a magnetic field.
False.
Radius is inversely proportional to charge (r ∝ 1/q), so a particle with a greater charge moves in a smaller circle, not a larger one.
What does the radius of curvature of a charged particle's track in a detector indicate?
Its momentum — a larger radius indicates a larger momentum, and a smaller radius indicates a smaller momentum.
Why does the radius of a charged particle's track typically decrease as it spirals inward through a detector?
The particle loses kinetic energy (and therefore momentum) by ionising other particles along its path, so r decreases since r ∝ p.
What does the direction of curvature of a particle's track indicate, and what rule is used to determine it?
The sign of the particle's charge. Fleming's Left Hand Rule is used to determine it.
Define pair creation, as seen in particle tracks.
When a particle track appears to begin 'out of nowhere', splitting into two tracks curving in opposite directions with the same radius — indicating the creation of a particle-antiparticle pair.
Why do particle and antiparticle tracks created in a pair-creation event have the same radius but curve in opposite directions?
They have the same mass (and therefore momentum), giving the same radius, but opposite charges, so the magnetic force — and hence curvature — acts in opposite directions.
Charge, energy and .......... are always conserved in interactions between particles.
Charge, energy and momentum are always conserved in interactions between particles.
True or False?
A charged particle track with an increasing radius indicates the particle is losing energy.
False.
An increasing radius indicates the particle's momentum (and kinetic energy) is increasing; a decreasing radius indicates energy loss through ionisation.
Define de Broglie wavelength.
The wavelength associated with a moving particle, given by $λ = \frac{h}{m v}$ , where h is the Planck constant, m is mass and v is velocity.
Why can high energy electron beams be used to determine the diameter of a nucleon?
Because at high energies, electrons have a de Broglie wavelength comparable to the size of the nucleon, so the scattering pattern produced can be analysed to determine the nucleon's diameter.
Why do electrons give a more precise measurement of nucleon size than alpha particles?
Electrons do not experience the strong nuclear force, so they can get extremely close to nucleons without interacting; alpha particles are made of protons and neutrons, which do interact via the strong force.
What can be resolved inside a nucleon using an electron beam of very high energy (and hence very small de Broglie wavelength)?
Individual quarks.
The de Broglie wavelength of an electron is .......... proportional to its velocity.
The de Broglie wavelength of an electron is inversely proportional to its velocity.
True or False?
Alpha particles give a more precise measurement of nucleon diameter than high energy electrons, because alpha particles are made of protons and neutrons.
False.
Electrons do not experience the strong nuclear force and so can approach nucleons without interacting, giving a more precise measurement; alpha particles do interact via the strong force, making them less precise probes.
Define annihilation.
When a particle meets its equivalent antiparticle, both are destroyed and their mass is converted into energy in the form of two gamma-ray photons emitted in opposite directions.
Define pair production.
When a photon interacts with a nucleus (or atom) and its energy is used to create a particle–antiparticle pair.
What is the energy carried by each photon produced when a particle and its antiparticle annihilate, in terms of the rest mass Δm of one particle?
$E_{p h o t o n} = h f = \frac{h c}{λ} = c^{2} Δ m$
What is the minimum total energy a photon must have to undergo pair production, in terms of the rest mass Δm of one particle produced?
$2 Δ E = 2 c^{2} Δ m$ , i.e. at least twice the rest mass energy of one particle.
When a particle and its antiparticle annihilate, their mass is converted into energy in the form of two .......... emitted in opposite directions.
When a particle and its antiparticle annihilate, their mass is converted into energy in the form of two gamma-ray photons emitted in opposite directions.
True or False?
A single photon with enough energy can undergo pair production on its own, without a nucleus present.
False.
A nearby nucleus (or nucleon) is essential so that both energy and momentum are conserved; a single photon alone cannot produce a particle–antiparticle pair without violating momentum conservation.
Define electronvolt.
The amount of energy transferred to an electron accelerated through a potential difference of 1 V. $1 eV = 1.6 \times 10^{- 19} J$
How do you convert an energy between joules and electronvolts?
Multiply electronvolts by 1.6 × 10^-19 to get the energy in joules; divide joules by 1.6 × 10^-19 to get the energy in electronvolts.
Why are units such as MeV/c² and GeV/c² convenient for particle physicists?
Because energy and mass are related by Einstein's mass-energy relation, $Δ m = \frac{Δ E}{c^{2}}$ so mass can be expressed in units of energy divided by c², which is useful in reactions such as annihilation and pair production.
What is 1 GeV/c² equivalent to, in kilograms?
$1 \frac{GeV}{c^{2}} = 1.78 \times 10^{- 27} kg$
1 eV is equivalent to .......... J.
1 eV is equivalent to 1.6 × 10^-19 J.
True or False?
1 GeV is a smaller unit of energy than 1 MeV.
False.
1 GeV = 10⁹ eV and 1 MeV = 10⁶ eV, so 1 GeV is 1000 times larger than 1 MeV.
Define time dilation.
The effect whereby a clock (and hence a particle's measured lifetime) moving at relativistic speed runs slower relative to a stationary observer.
Define length contraction.
The effect whereby the length of an object moving at relativistic speed is measured to be shorter, in the direction of motion, than when at rest.
Why are muons created high in the atmosphere, with a lifetime of only about 2 μs, detected in large numbers at sea level?
Because muons travel at relativistic speeds (e.g. 0.98c), so time dilation increases their observed lifetime to much longer than 2 μs, allowing them to survive the journey to sea level.
At approximately what fraction of the speed of light do relativistic effects on particle lifetime become significant?
Above about 90% of the speed of light (0.9c).
Length contraction means that particles moving at very high velocities travel .......... through detectors than expected without relativistic effects.
Length contraction means that particles moving at very high velocities travel further through detectors than expected without relativistic effects.
True or False?
Time dilation means a muon's own internal clock runs faster when it travels close to the speed of light, extending its lifetime.
False.
From a stationary observer's frame, the muon's clock appears to run slower, not faster; it is not that the muon's own clock speeds up, but that time passes more slowly for it relative to the observer, so its lifetime appears extended.

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