A-LevelPhysicsSuperposition9702/32 · May/June 2018 · Q220 Marks

In this experiment, you will investigate stationary wave patterns.

(a)You are provided with two pieces of string of different diameters. Each piece of string has a 10g mass attached to one end. Using the thinner string, assemble the apparatus as shown in [Figure 2.1]. The length of string between the hacksaw blade and the 10g mass is L, as shown in [Figure 2.1]. Measure and record L. L = [1]
(b)The length of hacksaw blade outside the blocks is x, as shown in [Figure 2.2]. When the end of the hacksaw blade is moved a small distance to one side and released, the string vibrates. For certain values of x, the string vibrates in stationary wave patterns. Examples of these patterns are shown in [Figure 2.3]. • Press down on the unclamped wooden block. • Move the end of the hacksaw blade a small distance to one side and release it. • Change x in small steps. Keep changing x, testing for a pattern at each step, until the pattern B with three loops is clearly produced. • Measure and record x. x = [2]
(c)Estimate the percentage uncertainty in your value of x. percentage uncertainty = [1]
(d)Calculate the value of λ in metres, using λ = 2L/3. λ = m[1]
(e)Justify the number of significant figures you have given for your value of λ.[1]
(f)You are provided with a card stating the mass per unit length μ of the string. • Record the value of μ from the card. μ = kg m⁻¹ • Calculate the frequency f of the vibrations, using f = 1/λ * sqrt(mg/μ) where m = 0.010kg and g = 9.81 ms⁻². f = Hz[1]
(g)Repeat (a), (b), (d) and (f) using the thicker string. L = x = λ = m μ = kgm⁻¹ f = Hz[3]
(h)(i)It is suggested that the relationship between f and x is f = k/x² where k is a constant. Using your data, calculate two values of k. first value of k = second value of k = [1]
(h)(ii)Explain whether your results support the suggested relationship.[1]
(i)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment. 1. 2. 3. 4.[4]
(i)(ii)Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures. 1. 2. 3. 4.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[1] (a) Value for L to nearest mm with unit and in range 50.0–75.0 cm.
[1] (b) Value for x with unit.
[1] (b) Raw value(s) of x to nearest mm and value on answer line in range 100–200 mm.
[1] (c) Absolute uncertainty in x value of 0.2-0.5cm and correct method of calculation to obtain percentage uncertainty. If repeated readings have been taken, then the absolute uncertainty can be half the range (but not zero) if the working is clearly shown.
[1] (d) Correct calculation of λ to the number of significant figures used by the candidate.
[1] (e) Justification linking s.f. in λ to s.f. in L.
[1] (f) Correct calculation of f.
[1] (g) Second values of L and x.
[1] (g) Quality: x increases as λ increases.
[1] (g) Second values of λ and f.
[1] (h)(i) Two values of k calculated correctly.
[1] (h)(ii) Valid comment consistent with the calculated values of k, testing against a numerical criterion specified by the candidate.
[1] (i)(i) Two readings are not enough to draw a (valid) conclusion (not "not enough for accurate results", "few readings”).
[1] (i)(i) Difficult to see string pattern.
[1] (i)(i) String pattern dies away quickly.
[1] (i)(i) Difficult to produce exact pattern required.
[1] (i)(i) Difficulty with wooden block e.g. doesn't grip blade/hard to hold down block and oscillate blade/view pattern at same time.
[1] (i)(i) Hacksaw/mass not at a node in the string pattern.
[1] (i)(ii) Take many readings and plot a graph or take more values of k and compare (not "repeat readings” on its own).
[1] (i)(ii) Put contrasting/black/white background behind string.
[1] (i)(ii) Use photo/video to assess pattern or description of workable method of producing continuous oscillations.
[1] (i)(ii) Add a scale/marks to hacksaw blade.
[1] (i)(ii) Clamp/put weight on the movable wooden block.
[1] (i)(ii) Workable solution to allow a node e.g. move excitation point away from node/use heavier mass.