AQA AS Level Physics Paper 2, June 2022: Question 18

✅ Correct Answer: C

The oscillations at two adjacent antinodes are in antiphase.

As the string oscillates, all points between two adjacent nodes (including the antinode) reach their maximum displacement at the same time, but adjacent antinodes (separated by a node) move in opposite directions. When one antinode is at its maximum positive displacement, the adjacent antinode is at its maximum negative displacement—meaning they are out of phase by 180 degrees (antiphase).

💡 Key Knowledge

• Nodes: Points of zero amplitude where destructive interference occurs permanently.
• Antinodes: Points of maximum amplitude where constructive interference occurs.
• Distance Rules: Distance between adjacent nodes = lambda / 2; distance between adjacent node and antinode = lambda / 4.
• Phase: All parts of a stationary wave between two adjacent nodes are in phase with each other. Crossing a node results in a 180 degree (pi radians) phase shift.
• Time Period: Every point on the stationary wave (except nodes) oscillates with the exact same frequency and time period.

🧠 Exam Technique

For multiple-choice conceptual questions:

1. Rapidly evaluate each option by visualising or sketching a fundamental or harmonic wave loop.
2. Rule out definitive false statements first (e.g., nodes have zero amplitude, not maximum amplitude).
3. Check your phase definitions carefully: points separated by a single node are always in antiphase.

❌ Common Errors to Avoid

• Confusing nodes with antinodes regarding amplitude (thinking nodes have maximum movement).
• Believing the distance between adjacent nodes is equal to a full wavelength (lambda) rather than half a wavelength (lambda / 2).
• Assuming different sections of a stationary wave oscillate at different frequencies or time periods.