Edexcel A-Level Physics AS: Materials

[Maximum number: 4]

A student was given a collection of old coins.
She placed the coins alongside a ruler, as shown, to determine the diameter and thickness of the coins.

Figure for Question 1 — Edexcel A-Level Physics AS

(a)

The mass of the 20 coins shown is 196 g .

Determine the average density of the coins.

Average density =

[ 2 ]

Use of $\rho=m / V$

- $\rho$ between 8000 and $8600 \mathrm{~kg} \mathrm{~m}^{-3}$

Allow ecf for V from 1(a) for both marks.

Example of calculation

$\rho=m / V$ $\rho=0.0098 \mathrm{~kg} / 1.18 \times 10^{-6} \mathrm{~m}^{3}$ $\rho=8300 \mathrm{~kg} \mathrm{~m}^{-3}$

(b)

Determine whether the coins could be made from brass.
density of brass $=8550 \mathrm{~kg} \mathrm{~m}^{-3} \pm 2 \%$

[ 2 ]

[Maximum number: 6]

A student determined the viscosity of a liquid using the falling-ball method.

(a)

When the ball is falling at terminal velocity the following equation applies

\text { drag force }=\text { weight of ball }- \text { upthrust }

The density of the liquid was known.
The student used a balance and a digital calliper to make measurements on the ball.
Describe how the student could use her measurements to calculate a value for the drag force acting on the ball.

[ 4 ]

(b)

When falling through the liquid, the ball reached terminal velocity.

The flow of liquid around the ball was laminar.
Calculate the viscosity of the liquid.
terminal velocity of ball $=5.4 \times 10^{-4} \mathrm{~m} \mathrm{~s}^{-1}$
radius of ball $=0.50 \times 10^{-2} \mathrm{~m}$
drag force $=1.1 \times 10^{-2} \mathrm{~N}$

Viscosity of liquid =

[ 2 ]

[Maximum number: 1]

A student determines the terminal velocity of a ball bearing as it falls through oil. He releases the ball bearing at point V and measures the time taken for it to fall a measured distance.

Figure for Question 3 — Edexcel A-Level Physics AS

Which two points should he use for the measured distance?

A

V and Y

B

W and Y

C

X and Y

D

W and Z

[Maximum number: 4]

A student determined the viscosity of a liquid using the falling-ball method.

When the ball is falling at terminal velocity the following equation applies

\text { drag force }=\text { weight of ball }- \text { upthrust }

The density of the liquid was known.
The student used a balance and a digital calliper to make measurements on the ball.
Describe how the student could use her measurements to calculate a value for the drag force acting on the ball.

[Maximum number: 2]

A student determined the viscosity of a liquid using the falling-ball method.

When falling through the liquid, the ball reached terminal velocity.

The flow of liquid around the ball was laminar.
Calculate the viscosity of the liquid.
terminal velocity of ball $=5.4 \times 10^{-4} \mathrm{~m} \mathrm{~s}^{-1}$
radius of ball $=0.50 \times 10^{-2} \mathrm{~m}$
drag force $=1.1 \times 10^{-2} \mathrm{~N}$

Viscosity of liquid =

[Maximum number: 2]

A student carried out an experiment to determine the Young modulus of constantan.
The student had a constantan wire with cross-sectional area A of $3.97 \times 10^{-7} \mathrm{~m}^{2}$ .
The unstretched length x of the wire was 4.00 m.

The student added slotted masses to the wire and determined the corresponding extensions. The student plotted a graph of force against extension, as shown.

Figure for Question 6 — Edexcel A-Level Physics AS

Show that the stiffness of the wire is about 1.3 x 10^4 N m^-1.

The gradient of the straight-line section is the stiffness. For example, $k=60\,\mathrm N/(4.6\times10^{-3}\,\mathrm m)=1.30\times10^4\,\mathrm{N\,m^{-1}}.$

[Maximum number: 3]

A student carried out an experiment to determine the Young modulus of a sample of stainless steel in the form of a wire. The student added weights to the wire and measured the corresponding extensions.

The wire had an unstretched length of 2.6 m . The diameter of the wire was $5.6 \times 10^{-4} \mathrm{~m}$ .
The student plotted a graph of weight against extension. The graph showed that the limit of proportionality was not exceeded.

The student's graph is shown below.

Weight / N

Figure for Question 7 — Edexcel A-Level Physics AS

Determine the Young modulus of stainless steel using your value for the gradient.
(3)

Young modulus =

Rearranges E= stress / strain to get E= gradient $\times_{\bar{A}}^{x}$

Or Rearranges E = stress / strain to get gradient $=\frac{A_{A}^{A} E}{x}$

Use of $A=\pi r^{2}$

Young modulus $=2 \times 10^{11} \mathrm{~Pa}$

(allow ecf from (b)(i))

Example of calculation

$A=\pi \times\left(2.8 \times 10^{-4}\right)^{2}=2.46 \times 10^{-7} \mathrm{~m}^{2}$ $E=1.85 \times 10^{4} \mathrm{~N} \mathrm{~m}^{-1} \times 2.6 \mathrm{~m} \div 2.46 \times 10^{-7} \mathrm{~m}^{2}=1.95 \times 10^{11} \mathrm{~Pa}$

[Maximum number: 1]

A student carried out an experiment to determine the Young modulus of a sample of stainless steel in the form of a wire. The student added weights to the wire and measured the corresponding extensions.

The wire had an unstretched length of 2.6 m . The diameter of the wire was $5.6 \times 10^{-4} \mathrm{~m}$ .
The student plotted a graph of weight against extension. The graph showed that the limit of proportionality was not exceeded.

State what is meant by the limit of proportionality.

[Maximum number: 3]

A student carried out an experiment to determine the Young modulus of a sample of stainless steel in the form of a wire. The student added weights to the wire and measured the corresponding extensions.

The wire had an unstretched length of 2.6 m . The diameter of the wire was $5.6 \times 10^{-4} \mathrm{~m}$ .
The student plotted a graph of weight against extension. The graph showed that the limit of proportionality was not exceeded.

The breaking stress for this stainless steel is known to be 480 MPa.

Deduce whether it is safe for the student to increase the weight to 100.0 N.

[Maximum number: 9]

A student carried out an experiment to determine the Young modulus of copper. She used the apparatus below to observe the position of a marker as a copper wire extended under increasing applied loads.

Figure for Question 10 — Edexcel A-Level Physics AS

(a)

Describe how the diameter of the wire should have been determined.

[ 3 ]

(b)

Explain why the sample of wire used in this experiment should be long and thin.

[ 6 ]

*16(c)

- This question assesses a student's ability to show a coherent and logically structured answer with linkages and fully-sustained reasoning.

- Marks are awarded for indicative content and for how the answer is structured and shows lines of reasoning.

- The following table shows how the marks should be awarded for indicative content.

Figure for Answer to Question (b) — Edexcel A-Level Physics AS

- The following table shows how the marks should be awarded for structure and lines of reasoning.

Total marks awarded is the sum of marks for indicative content and the marks for structure and lines of reasoning

Indicative content

- For long(er) wire, the extension will be large(r)

- (For the same load) extension is proportional to the original length

Or $\frac{\text { extension }}{\text { original length }}=$ constant

- For a thin(ner) wire, the extension will be large(r)

- (For the same load) extension is inversely proportional to cross-sectional area (may be explained in terms of $E, \sigma$ and $\varepsilon$ )

- The percentage uncertainty in the extension/length will be lower (although this will be greater for the cross-sectional area)

- A small(er) load can be used with a long/thin wire

[Maximum number: 5]

A steel object is held by an electromagnet. The magnetic force prevents the steel object falling.

The electromagnet is suspended from a support by a steel cable, as shown.

Figure for Question 11 — Edexcel A-Level Physics AS

The force-extension graph for the steel cable is shown below.

When the electromagnet is switched off, the steel object falls.
A student states that "the change in elastic strain energy stored in the cable will be transferred to the gravitational potential energy of the electromagnet".

Discuss the student's statement. You should add to the force-extension graph as part of your discussion.

Edexcel A-Level Physics AS 1.4 Materials Questions

Exam points

Covered syllabus points

Covered syllabus points

Question 1

Question (a)

Question (b)

Question 2

Question (a)

Question (b)

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question (a)

Question (b)

Question 11