Physics Year 11 - Module 3 - Lesson 12
The Doppler Effect
1. Key Ideas
When a siren rushes past, the pitch seems higher on approach and lower as it moves away. That apparent frequency shift is the Doppler effect, and it underpins police radar, weather Doppler systems, astronomy, and medical ultrasound.
- What the Doppler effect is
- Why wavefronts bunch up in front of a moving source
2. Success Criteria
By the end, you should be able to:
- What the Doppler effect is
- That approaching motion raises observed frequency
- That receding motion lowers observed frequency
3. Key Terms
4. Activity: Build the Lesson Map
Use the lesson to complete the table. Keep answers brief but specific.
| Prompt | Your answer |
|---|---|
| Main concept | |
| Important example | |
| Common mistake to avoid | |
| How this links to the next lesson |
5. Short Answer Questions
1. 7. Explain why an approaching source produces a higher observed frequency.
2. 8. A 600 Hz siren moves towards a stationary observer at 30 m/s. Take the speed of sound as 340 m/s. Find the observed frequency.
3. 9. Distinguish the moving-source and moving-observer Doppler equations, and explain one technological use of the effect.
6. Extend: Apply the Idea
A student gives a memorised answer about The Doppler Effect but does not use evidence or reasoning.
Improve the answer by writing a stronger response that uses accurate terminology, a relevant example and a clear explanation.
7. Multiple Choice
1. What is the best first step when answering a question about The Doppler Effect?
A. Identify the key concept being tested
B. Write every fact from memory
C. Ignore the command word
D. Skip examples and evidence
2. Which answer would show stronger understanding of The Doppler Effect?
A. An answer with accurate terms and reasoning
B. A copied definition only
C. A single-word response
D. An answer with no example
3. What should you do if a question asks you to explain?
A. Link the idea to a reason or cause
B. List unrelated facts
C. Only draw a diagram
D. Write the shortest possible answer
8. Success Criteria Proof
Finish with evidence that you can do each success criterion.