Why is the strong nuclear force needed to hold atomic nuclei together?

Neutrons are negatively charged and need to be held away from the positive protons Protons are all positively charged and repel each other electromagnetically — the strong force must overcome this repulsion Without the strong force, electrons would enter the nucleus and cancel the protons The strong force is needed because gravity cannot hold nucleons together

What are quarks, and how does the strong force relate to them?

Quarks are subatomic particles that carry negative charge; the strong force repels them from the nucleus Quarks are fundamental constituents of electrons; the strong force is their electromagnetic interaction Quarks are the fundamental constituents of protons and neutrons; the strong force (via gluon exchange) binds quarks together inside these particles Quarks are types of photons that the strong force uses to transmit energy

What is the particle that carries the strong nuclear force between quarks?

The photon The gluon The W boson The pion

Why can isolated quarks never be observed — only quarks bound inside protons, neutrons, or other hadrons?

Quarks are too small to be detected by any instrument Colour confinement: the strong force becomes stronger as quarks are pulled apart, making it impossible to separate them Quarks move too fast to be isolated — they always combine before detection Isolated quarks decay immediately into electrons, which are then observed instead

What role do neutrons play in stabilising atomic nuclei?

Neutrons add negative charge to balance the protons' positive charge Neutrons slow down the protons to reduce their repulsive energy Neutrons add strong force binding without adding electromagnetic repulsion — they act as a 'buffer' between protons Neutrons block the electromagnetic force between protons

The strong force becomes repulsive at very short distances (less than ~0.8 fm). What is the consequence of this short-range repulsion?

It causes nucleons to emit gamma radiation when compressed It prevents nucleons from collapsing into each other, giving nucleons a definite size It causes alpha particles to be ejected from the nucleus It creates the electromagnetic repulsion between protons

Which of these describes 'nuclear binding energy'?

The kinetic energy of protons moving inside the nucleus The energy that must be supplied to completely separate all the nucleons in a nucleus — it equals the mass defect × c² The energy released when an electron jumps to a lower energy level The force between protons measured in joules per metre

Why does nuclear fusion release energy for light elements (like hydrogen and helium) but nuclear fission releases energy for heavy elements (like uranium)?

Fusion always releases energy; fission always absorbs energy Fission releases energy because splitting creates smaller, faster particles Iron-56 has the maximum binding energy per nucleon — nuclei on both sides of iron can release energy by moving toward iron (fusion for lighter, fission for heavier) The energy comes from the electromagnetic repulsion between protons, not the strong force

Evidence for quarks came from deep inelastic scattering experiments at SLAC (Stanford) in the 1960s. What did these experiments show?

Protons were found to be made of electrons and positrons High-energy electrons fired at protons scattered at large angles, indicating hard, point-like scattering centres (quarks) inside the proton Protons were confirmed to be fundamental, indivisible particles The experiments showed that the strong force does not exist inside the proton

A proton is made of two up quarks and one down quark. If up quarks have charge +2/3 e and down quarks have charge −1/3 e, what is the total charge of a proton?

+2/3 e 0 (neutral) +1 e +3 e