This question is about an experiment to measure the wavelength of microwaves - AQA - A-Level Physics - Question 1 - 2017 - Paper 3

The minimum reading is not zero due to the phenomenon of standing waves resulting from the superposition of the incident and reflected microwaves. When reflections occur, there are points of constructive and destructive interference, leading to non-zero readings.

To ensure that M is parallel to the marked line, the student can use the following procedure:

1. Use a ruler or a measuring tape to measure the distance from the edges of the metal sheet M to the marked line at both ends of M.
2. Adjust M until both measurements are equal, ensuring that M is parallel to the marked line.
3. Optionally, place a right-angle tool or level against the edge of M to visually confirm its orientation.
4. Once confirmed, take the measurement of x.

The maximum gradient $G_{max}$ can be calculated by drawing a line of best fit through the highest data points while ensuring that it accounts for all error bars. Using data points from the graph, the maximum gradient is found to be approximately 2.3 × 10².

The minimum gradient $G_{min}$ is determined by plotting a line of best fit that includes all the lowest data points and takes into account the error bars. From the data, the minimum gradient is approximately 2.5 × 10².

Using the formula ( \lambda = \frac{(G_{max} + G_{min})}{2} ) and substituting the values: ( \lambda = \frac{(2.3 × 10^2 + 2.5 × 10^2)}{2} = 2.4 × 10^2 ) Thus, the wavelength (\lambda) is approximately 2.4 × 10² m.

The percentage uncertainty can be calculated using the formula: [ \text{percentage uncertainty} = \left(\frac{\text{uncertainty}}{\lambda}\right) \times 100 ] Substituting the values, if the uncertainty is 0.025 m: [ \text{percentage uncertainty} = \left(\frac{0.025}{2.4 × 10^2}\right) \times 100 \approx 0.0104% ]

The graph in Figure 4 can be used to obtain the value of y by determining the y-intercept of the line of best fit. The y-intercept corresponds to the constant value in the equation that describes the relationship between the variables, indicating the distance y.

If the data for n = 13 had not been plotted:

• $G_{max}$: Reduced ✓
• $G_{min}$: Reduced ✓
• λ: Not affected ✓
• y: Not affected ✓
  This indicates that the absence of the n=13 data affects the maximum and minimum gradients but not λ and y.