IB PHYSICS SL (Standard level)- 2024 – Practice Questions- All Topics
Topic 7.3 – The structure of matter
Topic 7 Weightage : 7%
All Questions for Topic 7.3 – Quarks, leptons and their antiparticles , Hadrons, baryons and mesons , The conservation laws of charge, baryon number, lepton number and strangeness , The nature and range of the strong nuclear force, weak nuclear force and electromagnetic force, Exchange particles, Feynman diagrams, Confinement, The Higgs boson
Question
A particle reaction is
Which conservation law is violated by the reaction?
A Baryon number
B Charge
C Lepton number
D Momentum
▶️Answer/Explanation
Ans: B
Considering Charge on the both sides of equation:
\(p= +1,\; \bar{e}=-1 \; \bar{\nu _\mu} =0\)
on right side
\(n= 0\; \mu^+ =+1 , \nu _e =0\)
Hence \(1-1+0 \neq 0+1+0\)
Hence Charge Conservation is violated.
Question
Which Feynman diagram shows beta-plus (β+) decay?
▶️Answer/Explanation
Markscheme
A
In beta-plus (β+) decay process, a positron and a neutrino are created and emitted from the nucleus.
\(p\rightarrow n+e^{+} + \nu_e\)
we look deeper and see that a proton (uud) can change into a neutron (udd) by changing a up quark into an down quark.We now view the fundamental beta-decay process as
\(u\rightarrow d+e^{+} + \nu_e\)
Question
The Feynman diagram shows a particle interaction involving a W– boson.
Which particles are interacting?
A. U and Y
B. W– boson and Y
C. X and Y
D. U and X
▶️Answer/Explanation
Markscheme
C
Neutron-neutrino Interaction
When a neutron interacts with a neutrino, a W– boson is released as the exchange particle, which in turn interacts with the neutrino to form the β– particle.
Question
The reaction p+ + n0 → p+ + \(\pi \)0 does not occur because it violates the conservation law of
A. electric charge.
B. baryon number.
C. lepton number.
D. strangeness.
▶️Answer/Explanation
Markscheme
B
Baryon number of all other particle is 0
Now in given equation we have
for left side of equation
for \( p^+ , B = 1\)
for \(n^0, B =1\)
For right side of equation
for \(p^+ , B = 1\)
for \(\pi^0\)
Hence \( 1+1 \neq 1+0\)
Question
As quarks separate from each other within a hadron, the interaction between them becomes larger. What is the nature of this interaction?
A. Electrostatic
B. Gravitational
C. Strong nuclear
D. Weak nuclear
▶️Answer/Explanation
Markscheme
C
Particles with electric charge interact through the electromagnetic force by exchanging virtual photons. Leptons can also interact with each other and with quarks through the weak force, via massive W and Z particles as messengers. In addition, quarks interact with each other through the color force. The electromagnetic and weak forces are different manifestations of the same force, called the electroweak force.
The Strong Force
A theory of the strong force—that is, the force that acts between quarks to bind hadrons together The messenger particles in this case are called gluons and, like the photon, they are predicted to be massless.The theory assumes that each “flavor” of quark comes in three varieties that, for convenience, have been labeled red, yellow, and blue. Thus, there are three up quarks, one of each color, and so on.The antiquarks also come in three colors, which we call antired, antiyellow, and antiblue.
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