Edexcel A-Level Physics A2 Unit 6 Practical Skills II

Practise Edexcel A-Level Physics A2 Unit 6 Practical Skills II with graphical methods, experimental design, temperature control and data critique.

[Maximum number: 12]

A student added small lead spheres to a test tube. The student placed the test tube in a small beaker of water. The test tube floated as shown.

Figure for Question Unit 6: Practical Skills in Physics II question 1 — Edexcel A-Level Physics A2

The student gave the test tube a small vertical displacement. The test tube then oscillated vertically.

(a)

The student measured the time period T of the oscillations using a stopwatch. She repeated the measurement of T and calculated a mean.

[ 5 ]

(i)

Describe two other techniques she should use to determine T.

[ 2 ]

(ii)

The measurements are $5T/\mathrm{s}=3.43,3.36,3.28,3.49$ . Calculate the mean value of T and its uncertainty.

Figure for Question (ii) — Edexcel A-Level Physics A2

[ 3 ]

The mean is $T= rac{3.43+3.36+3.28+3.49}{5 imes4}=0.678\,\mathrm{s}=0.68\,\mathrm{s}.$ The half-range uncertainty is $(3.49-3.28)/(5 imes2)=0.021\,\mathrm{s}=0.02\,\mathrm{s}.$ Thus $T=0.68\pm0.02\,\mathrm{s}$ .

(b)

The student estimated that the diameter of the test tube was approximately 2 cm .

Explain why vernier calipers are a suitable instrument to measure the diameter. Your answer should include a calculation.

Figure for Question (b) — Edexcel A-Level Physics A2

[ 2 ]

(c)

The student replaced the water with another liquid. The period is given by $T=\sqrt{ rac{16\pi m}{D^2 ho g}},$ where D is the test-tube diameter, m is the mass of the test tube and spheres, and ho is the liquid density.

[ 5 ]

(i)

Show that the percentage uncertainty in ho is about $4\%$ .

[ 3 ]

Because $ho\propto D^{-2}T^{-2}$ , $%U( ho)=2 rac{0.01}{2.38} imes100+2 rac{0.01}{0.61} imes100=4.12\%,$ about $4\%$ .

(ii)

The density of glycerol is $1260\,\mathrm{kg\,m^{-3}}$ . Deduce whether the liquid could be glycerol.

[ 2 ]

The upper limit is $1190(1+0.041)=1239\,\mathrm{kg\,m^{-3}}$ , below $1260\,\mathrm{kg\,m^{-3}}$ . Therefore the liquid may not be glycerol.

[Maximum number: 3]

Two identical capacitors were connected in series and charged. They were then discharged through a resistor and ammeter.
A student investigated how the current in the resistor varied as the capacitors discharged.

(a)

State one safety precaution the student should take.

[ 1 ]

(b)

The student repeated the investigation but used a data logger instead of a stopwatch and an ammeter.

Suggest why using a data logger would improve this investigation.

[ 2 ]

[Maximum number: 11]

A student investigated the damping of a rotational pendulum using the apparatus shown.

Figure for Question Unit 6: Practical Skills in Physics II question 3 — Edexcel A-Level Physics A2

When the metal rod is rotated through an angle and released, the rod performs angular oscillations about a vertical axis through the wire. The plastic sheets dampen the oscillations as they move through the air.

(a)

The student displaced the metal rod by a large angle. He recorded the maximum displacement angle every 10 oscillations.

n	$heta/^{\circ}$
10	124
20	82
30	55
40	37
50	25
60	16

Figure for Question (a) — Edexcel A-Level Physics A2

[ 11 ]

(i)

Plot a graph of $\ln heta$ against n on the grid opposite. Use the additional column for your processed data.

[ 5 ]

(ii)

Determine the value of $\lambda$ from the graph.

[ 3 ]

Using a large triangle on the best-fit line gives a gradient of about -0.0405. Since the gradient is $-\lambda$ ,

$\lambdapprox0.041$

(to 2 or 3 significant figures, with no unit).

(iii)

The student claimed that the initial displacement angle was greater than $180^{\circ}$ . Deduce whether this claim is correct.

[ 3 ]

From $\ln heta=\ln heta_0-\lambda n$ ,

$\ln heta_0=\ln heta+\lambda n=3.2+(0.041)(50)=5.25,$

so $heta_0=e^{5.25}=191^{\circ}$ . This is greater than $180^{\circ}$ , so the claim is correct.

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Covered syllabus points

Unit 6: Practical Skills in Physics II question 1

Question (a)

Question (i)

Question (ii)

Question (b)

Question (c)

Question (i)

Question (ii)

Unit 6: Practical Skills in Physics II question 2

Question (a)

Question (b)

Unit 6: Practical Skills in Physics II question 3

Question (a)

Question (i)

Question (ii)

Question (iii)