# 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.

……………………………………………………………………………………………………………………. 

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

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

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

elementary charge.



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

………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………. 
(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.

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

nucleon number = ………………………………………………………
proton number = ………………………………………………………


(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.

………………………………………………………………………………
……………………………………………………………………………………… 
(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 

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

……………………………………………………….  [Total: 6]