Materials assessed Homework

 

3.4 Materials MS

 

M1.          (a)    The candidate’s writing should be legible and the spelling, punctuation and grammar should be sufficiently accurate for the meaning to be clear. The candidate’s answer will be assessed holistically. The answer will be assigned to one of three levels according to the following criteria.

High Level (Good to excellent): 5 or 6 marks

The information conveyed by the answer is clearly organised, logical and coherent, using appropriate specialist vocabulary correctly. The form and style of writing is appropriate to answer the question.

Candidate must suggest

·        drawing a graph of F vs ΔL (or vice versa)

·        AND that k is in some way linked to the gradient

·        AND use of a suitable named instrument to measure or determine extension

·        AND 1 further means of reducing uncertainty: repeats / minimum 8 different readings / use of vernier scale / check values of mass with balance / parallax elimination with set square, pointer in contact with scale, mirror.

For 6 marks:

must also give suitable range at least up to 10N but not beyond 20N (accept ‘up to 20N’ / ‘not beyond 20N’)

AND minimum 8 different readings OR parallax elimination must be included

AND repeats must be included

AND correctly explains how k is obtained from their graph.

Intermediate Level (Modest to adequate): 3 or 4 marks

The information conveyed by the answer may be less well organised and not fully coherent. There is less use of specialist vocabulary, or specialist vocabulary may be used incorrectly. The form and style of writing is less appropriate.

Candidate must suggest:

·        to measure / determine extension OR initial and final length

·        AND to use F = k ΔL or k = F / ΔL
OR drawing a graph of F vs ΔL (or vice versa)

·        AND use of suitable instrument to measure extension
OR 1 means of reducing uncertainty:
repeats / use of vernier scale / check values of mass with balance / parallax elimination with set square,    pointer in contact with scale,
mirror / minimum 8 different readings / graphical approach

For 4 marks, uncertainty comment AND instrument required

Low Level (Poor to limited): 1 or 2 marks

The information conveyed by the answer is poorly organised and may not be relevant or coherent. There is little correct use of specialist vocabulary. The form and style of writing may be only partly appropriate.

Any relevant statement from the marking points above

For 2 marks: must mention minimum two points including:

·        to measure / determine extension OR initial and final length

6

(b)     (i)     (k = 2 × 85 = 170 (N m^–1) )

(ΔL = F / k =) 15 / 170 ( or 7.5 / 85 )

= 0.088  (m) (0.0882)

2

(ii)     (k = ½ × 85 = 42.5 )

(ΔL = F / k = ) 15/42.5 ( or 2 x 15/85)

= 0.35  (m) (0.3529)

2

(iii)     (W = ½ FΔL or ½ k ΔL²)

= ½ × 15 × 0.0882 ( or 2 x ½ × 7.5 × 0.0882)  ecf 5bi

= 0.66  (J) (0.6615) ecf 5bi

2

(iv)     (series) greater  ecf for answer ‘less’ or ‘same’ where candidates
incorrect answers to bi and bii support this.

extension is more (in series) and the force is the same
(in both situations)

AND quotes Energy stored = ( ½ )Fs or ½ FΔL OR energy proportional to
extension

3

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M2.          (a)     tensile stress: (stretching) force (applied) per unit
cross-sectional area (1)
tensile strain: extension (produced) per unit length (1)

2

 

(b)     Hooke’s law (or stress  strain) obeyed up to point A (1)
A is limit of proportionality  (1)
elastic limit between A and region B (1)
region C shows plastic behaviour or wire is ductile  (1)
region B to C wire will not regain original length  (1)
beyond region C necking occurs (and wire breaks) (1)

max 5

QWC

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M3.          (a)    

Suitable scale on both axes (eg not going up in 3s) and > ½ space used

≥ points correct (within half a small square)

line is straight up to at least stress = 2.5 × 10⁸ and curve
is smooth beyond straight section

3

(b)     understanding that E = gradient (= Δy/Δx)

allow y/x if line passes through origin

= 1.05 × 10¹¹ (Pa) (allow 0.90 to 1.1) ecf from their line in (a)
if answer outside this range and uses a y value ≥ 2

when values used from table;

•        two marks can be scored only if candidates line passes
through them

•        one mark only can be scored if these points are not on their line

2

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