IB Physics HL S: Physics Skills

Practise IB Physics HL skills through shared-core and HL work on units, uncertainties, graphs, instruments and measurements in physical contexts.

Covered syllabus points

S1.1 Experimental techniques S1.2 Technology S1.3 Mathematics S2.1 Exploring and designing S2.2 Collecting and processing data S2.3 Concluding and evaluating

[Maximum number: 4]

This question is about the use of radioactive isotopes.

(a)

Radiologists working with radioactive sources wear a film badge. Discuss the function of a film badge.

[ 3 ]

(b)

One of the side effects of the use of Sr -89 is the reduction of white blood cells in the body, leaving the patient prone to infections. Outline one ethical implication of the choice between using Sr-89 to treat bone cancer and not carrying out treatment.

[ 1 ]

[Maximum number: 2]

This question is in two parts. Part 1 is about solar power and climate models. Part 2 is about digital storage of data.

A charge-coupled device (CCD) enables large amounts of photographic data to be captured and stored.

Outline how the image on a CCD is digitized.

[Maximum number: 1]

A girl rides a bicycle that is powered by an electric motor. A battery transfers energy to the electric motor. The emf of the battery is 16 V and it can deliver a charge of 43 kC when discharging completely from a full charge.

The maximum speed of the girl on a horizontal road is $7.0 \mathrm{~m} \mathrm{~s}^{-1}$ with energy from the battery alone. The maximum distance that the girl can travel under these conditions is 20 km .

Show that the time taken for the battery to discharge is about $3 \times 10^{3} \mathrm{~s}$ .

time taken $\frac{2.0 \times 10^{4}}{7} \boldsymbol{<} \boldsymbol{=} \mathbf{2 8 6 0} \boldsymbol{\mathrm { s }} \boldsymbol{>} \boldsymbol{>} \boldsymbol{=} \mathbf{2 9 0 0} \boldsymbol{<} \boldsymbol{\mathrm { s }} \boldsymbol{>} \boldsymbol{>} \boldsymbol{}$

Must see at least two s.f.

[Maximum number: 8]

A group of students is trying to determine the density and the viscosity of a liquid.

To determine the density, they use a balance to read the mass m of a sphere in air and immersed in the liquid.

They use a sphere of volume $V=1.827 \times 10^{-7} \mathrm{~m}^{3}$ .
The readings are $m_{\text {air }}=1.427 \mathrm{~g}$ in air and $m_{\text {immersed }}=1.208 \mathrm{~g}$ in the liquid.
The readings are different due to buoyancy. The buoyancy force $F_{\mathrm{b}}$ is given by

F_{\mathrm{b}}=\rho V g

where V is the volume of the sphere and $\rho$ is the density of the liquid.

(a)

State the level of precision in the measurement of m.

[ 1 ]

(b)

To determine the viscosity, they immerse the sphere in the liquid and drop it from rest.
They collect values and plot a graph of the position d of the sphere from the moment they drop it. They verify that the sphere reaches terminal velocity $v_{t}$ after 0.5 s .

Draw the line of best fit on the graph.

[ 2 ]

(c)

They repeat the experiment several times and estimate an average for

v_{\mathrm{t}}=(0.71 \pm 0.05) \mathrm{ms}^{-1}

They use the equation

\eta=\frac{m_{\mathrm{air}} g-\rho V g}{6 \pi r v_{\mathrm{t}}}

where
r= radius of the sphere,
$v_{\mathrm{t}}=$ terminal velocity of the sphere,
$\eta=$ viscosity of the liquid.
The radius r of the sphere is 3.520 mm .

Calculate the viscosity of the liquid and its absolute uncertainty. Ignore uncertainties in the mass, radius and volume of the sphere. Give your answer in the form $\eta \pm \Delta \eta$ , to an appropriate number of significant figures, including units.

[ 4 ]

$\begin{aligned} \eta=0.2512 7 \% \text { OR } 0.02 \eta=0.25 \pm 0.02 \text { Pa s OR } \mathrm{kg} \mathrm{~m}^{-1} \mathrm{~s}^{-1} \end{aligned}$

MP1 and MP2 are for the calculations, accept any number of SF,

MP3 is for the matching precision of the value and its uncertainty. ECF may apply but uncertainty may only have 1 SF .

Allow other suitable units such as $\mathrm{Nm}^{-2} \mathrm{~s}$

(d)

The students search literature values and find the viscosity of this liquid to be 0.24 , when expressed in SI base units.

Suggest a conclusion reached by the students.

[ 1 ]

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Covered syllabus points

S Skills in Physics question 1

Question (a)

Question (b)

S Skills in Physics question 2

S Skills in Physics question 3

S Skills in Physics question 4

Question (a)

Question (b)

Question (c)

Question (d)