# CIE AS & A Level Physics : 11.2 Fundamental particles – Exam style question – Paper 2

### Question

(a) A proton in a nucleus decays to form a neutron and a $$β^+$$ particle.
(i) State the name of another lepton that is produced in the decay.

……………………………………………………………………………………………………………………. [1]

(ii) State the name of the interaction (force) that gives rise to this decay.

……………………………………………………………………………………………………………………. [1]
(iii) State which of the three particles (proton, neutron or $$β^+$$ particle) has the largest ratio of

charge to mass.
……………………………………………………………………………………………………………………. [1]
(iv) Use the quark model to show that the charge on the proton is +e, where e is the

elementary charge.

[2]

(v) The quark composition of the proton is changed during the decay.
Describe the change to the quark composition.

………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. [1]
(b) A nucleus X and a nucleus Y are accelerated by the same uniform electric field.

(i) Determine the ratio

ratio = …………………………………………………
(ii) Determine the ratio

ratio = …………………………………………………

(iii) Nucleus X is at rest in the uniform electric field at time t = 0.
The field causes nucleus X to accelerate so that it moves through the field.
On Fig. 6.1, sketch the variation with time t of the acceleration a of nucleus X due to the

field.

Ans:

(a)(i) (electron) neutrino

(a)(ii) weak (nuclear force/interaction)

(a)(iii) $$β^+$$ (particle)

(a)(iv) (quark structure is) up up down or uud
$$(2 / 3)e + (2 / 3)e– (1 / 3)e = (+)e$$

(a)(v) up up down changes to up down down or uud→ udd

or
up changes to down or u→ d

(b)(i) F = Eq C
ratio = 6 / 8 = 0.75

(b)(ii) ratio = 0.75 × (16 / 12) = 1.0

(b)(iii) horizontal straight line at a non-zero value of a

### Question

(a) A nucleus of sodium-22  decays by emitting a $$β^+$$ particle. A different nucleus is formed by the decay.
(i) State the name of another lepton that is produced by the decay.

…………………………………………………………….. [1]
(ii) Determine the nucleon number and the proton number of the nucleus that is formed by the decay.

nucleon number = ………………………………………………………
proton number = ………………………………………………………
[2]

(iii) The quark composition of a nucleon in the sodium-22 nucleus is changed during the decay.

Describe the change to the quark composition of the nucleon.

………………………………………………………………………………
……………………………………………………………………………………… [1]
(b) A baryon consists of quarks that are the same flavour (type). The charge of the baryon is –2e, where e is the elementary charge.

(i) Calculate, in terms of e, the charge of each quark.

charge = ……………………………………………… e [1]

(ii) State a possible flavour (type) of the quarks.

………………………………………………………. [1] [Total: 6]