DP Physics (first assessment 2025)

Question EXE.2.HL.TZ0.1

Date	Example questions Example questions	Marks available	[Maximum mark: 20]	Reference code	EXE.2.HL.TZ0.1
Level	HL	Paper	2	Time zone	TZ0
Command term	Calculate, Determine, Estimate, Explain, Outline, Show that, State	Question number	1	Adapted from	N/A

[Maximum mark: 20]

EXE.2.HL.TZ0.1

A nuclear power station uses uranium-235 ( ${}_{92}^{235}U$ ) as fuel. One possible fission reaction of ${}_{92}^{235}U$ is

${}_{92}^{235}U + {}_{0}^{1}n \to {}_{52}^{132}{Te} + {}_{40}^{101}{Zr} + 3 {}_{0}^{1}n$

(a.i)

State the principal energy change in nuclear fission.

[1]

Markscheme

Mass-energy «of uranium» into kinetic energy of fission products ✓

(a.ii)

The energy released in the reaction is about 180 MeV. Estimate, in J, the energy released when 1 kg of ${}_{92}^{235}U$ undergoes fission.

[3]

Markscheme

Mass of uranium nucleus $\approx 235 u$ ✓

$\frac{energy}{mass} = \frac{180 \times 10^{6} \times 1.60 \times 10^{- 19}}{235 \times 1.661 \times 10^{- 27}}$ ✓

$7.4 \times 10^{13}$ «J» ✓

One of the products of the reaction is a nucleus of tellurium-132 ( ${}_{52}^{132}{Te}$ ). The diagram shows the location of ${}_{52}^{132}{Te}$ in a table of nuclides in which the proton number of a nuclide is plotted against its neutron number. The nuclides shown in black are stable.

(b.i)

State and explain the decay mode of ${}_{52}^{132}{Te}$ .

[2]

Markscheme

beta minus decay ✓

${}_{52}^{132}{Te}$ has more neutrons / higher $\frac{N}{Z}$ ratio than stable nuclides of similar A «and beta minus reduces $\frac{N}{Z}$ » ✓

A sample of pure ${}_{52}^{132}{Te}$ is extracted from some spent nuclear fuel from the reactor. The graph shows how the natural logarithm of the activity A of the sample varies with time t.

(b.ii)

Calculate, in s⁻¹, the initial activity of the sample.

[1]

Markscheme

$e^{25} = 7.2 \times 10^{10}$ «s⁻¹» ✓

(b.iii)

Show that the decay constant of a nuclide is given by −m, where m is the slope of the graph of lnA against t.

[1]

Markscheme

Takes ln of both sides of $A = A_{0} e^{- λ t}$ , leading to $\ln A = \ln A_{0} - λ t$ ✓

«hence slope $= - λ$ » ✓

(b.iv)

Determine, in days, the half-life of ${}_{52}^{132}{Te}$ .

[2]

Markscheme

Slope =«−» $2.5 \times 10^{- 6}$ «s⁻¹» ✓

$T_{\frac{1}{2}} =$ « $\frac{\ln 2}{2.5 \times 10^{- 6} \times 60 \times 60 \times 24} =$ » 3.2 «days» ✓

The nuclear power station uses high-pressure gas to power an electrical generator. The gas circulates between the heat exchanger and the turbine of the generator.

(c.i)

Outline the role of the heat exchanger in a nuclear power station.

[1]

Markscheme

Collects thermal energy from the coolant and delivers it to the gas ✓

Prevents the «irradiated» coolant from leaving the reactor vessel ✓

The working gas of the turbine undergoes a cyclic change that can be modelled as the cycle ABCDA shown in the pressure-volume diagram.

The cycle consists of an isobaric expansion AB, adiabatic expansion BC, isobaric compression CD and adiabatic compression DA. The cycle is drawn for a quantity of 1.0 mol of monatomic ideal gas.

(c.ii)

Calculate the maximum temperature of the gas during the cycle.

[3]

Markscheme

Correct read offs of pressure and volume at B ✓

$8.0 \times 10^{6} \times 1.6 \times 10^{- 3} = 1.0 \times 8.31 \times T$ ✓

$T = 1500$ «K» ✓

The following data are given about the work W done by the gas and thermal energy Q transferred to the gas during each change:

Change	W / kJ	Q / kJ
AB	8.23	20.58
BC	9.11	0
CD	−4.32	−10.81
DA	−3.25	0

(c.iii)

Outline why the entropy of the gas remains constant during changes BC and DA.

[1]

Markscheme

From $Δ S = \frac{Δ Q}{T}$ , the change in entropy is zero when $Δ Q = 0$ ✓

(c.iv)

Determine the efficiency of the cycle.

[2]

Markscheme

Net work done = « $8.23 + 9.11 - 4.32 - 3.25$ » 9.77 «kJ» ✓

Efficiency =« $\frac{9.77}{20.58} =$ » 0.47 ✓

During a maintenance shutdown of the reactor, the gas supply to the turbine is cut off and the turbine gradually comes to rest. The diagram shows how the angular speed of the turbine varies with time t.

(d)

Show that the rotational kinetic energy of the turbine decreases at a constant rate.

[3]

Markscheme

Rotational KE is proportional to $ω^{2}$ ✓

Calculation of $ω^{2}$ for at least four points, e.g. {96.1, 76.7, 57.6, 38.4, 19.3}×10³

Shows that the differences in equal time intervals are approximately the same, e.g. {19.4, 19.1, 19.2, 19.1, 19.3}×10³✓

Allow a tolerance of ±1×10³s⁻² from the values stated in MP2.