Paper 3 Practicals

Question 1

What equipment is required for the Investigation into the variation of the frequency of stationary waves on a string with length, tension and mass per unit length of the string

Answer 1

○ Signal generator
○ Vibration generator
○ Stand
○ Pulley
○ Wooden bridge
○ 100g masses with holder
○ Metre ruler
○ 1.5m long string
○ Balance

Question 2

What is the method for the Investigation into the variation of the frequency of stationary waves on a string with length, tension and mass per unit length of the string

Answer 2

○ Set up the apparatus as shown in the diagram.
○ Adjust the length l so that it is 1.000m, measured using the metre ruler.
○ Increase the frequency f until the string oscillates at the first harmonic. Read and
record f.
○ Reduce l by 0.100m and adjust f again until it oscillates at the first harmonic.
Measure and record f and repeat this, reducing l by 0.100m each time down to
0.500m.
○ Repeat the experiment twice more and find and record the mean f for each l.
○ Measure the mass of the string on the balance and record it.

Question 3

Explain the graphs and calculations for the Investigation into the variation of the frequency of stationary waves on a string with length, tension and mass per unit length of the string

Answer 3

Plot a graph of the mean value of f against 1/l and draw a line of best fit. The wave
speed will be two times the gradient.
2f
○ λ = 2l ⇒ v = 2f l = 1 = 2G where G is the gradient.

○ The tension of the string is equal to the weight of the hanging mass (if 100g, 0.981N) and its mass per unit length can be found by dividing the mass of the string by its length (1.5m).

The speed of the wave is also given by v = √ T/μ ​which can be compared to the value obtained from the graph

Question 4

Identical ring magnets A and B are arranged on a cylindrical wooden rod. The magnets’ magnetic poles are on their largest faces. When placed with like poles in opposition, the magnets repel one another as shown in Figure 1.
The plan and sectional views in Figure 1 identify the dimensions of these magnets.
Each magnet has a circular cross-section and the central hole is circular
State precautions the student should take to reduce the effect of systematic and random errors when making this measurement.

Answer 4

to reduce the impact of systematic error: tare [zero] the callipers before use
OR
take reading with callipers fully closed (at some stage) and subtract from readings 1✔
to reduce the impact of random error: take measurement several times for different diameters/directions and calculate mean
OR
take measurement several times for different diameters to check for anomalies

Question 5

This question is about an experiment with a retractable steel tape measure.
The tape measure is placed at the edge of the bench and about 1 m of the steel tape is extended so that it overhangs the bench.
The tape is then locked in this position to stop it from retracting.
A student measures the dimensions x and y, the horizontal and vertical displacements of the free end of the tape, as shown in Figure 1.
Describe a suitable procedure the student could use to measure y

Answer 5

technique:
at least one instance seen where a metre ruler is made vertical using a set-square in contact with the floor 1✔
strategy:
(use a metre ruler to) measure the height of the free end of the tape (above the floor) and the height of the tape at the bench [height of the bench];
y = difference between these heights 2