Physical Science Grade 12(Doppler effect )


Introduction video

Topic: Doppler effect

The below video is the introduction of the lesson which mainly focus on the lesson outcomes and what is to be discussed in class.



Practice Task 

Topic: Doppler Effect 


1. An ambulance is moving towards a stationary listener at a constant speed of 30 m/s. The siren of the ambulance emits sound waves having a wavelength of 0.28 m. TAKE THE SPEED OF SOUND IN AIR AS 340 m/s.

1.1.1 Define Doppler Effect in words.  (2)

1.1.2 Calculate the frequency of the sound waves emitted by the siren as heard by the ambulance driver. (3)

1.1.3 Calculate the frequency of the sound waves emitted by the siren as heard by the listener. (5)

1.1.4 Explain how this Effect can help a blind person waiting to cross the road. (2)

1.1.5 State one use of Doppler Effect  in medicine 


What is Doppler Effect? Definition, Formula, Doppler Effect Example and Applications


•The above links may be used to help you to attempt your given task, They explain how Doppler occur and help you gain more understanding about this phenomenon.

•You need to take note on the Formula of Doppler effect especially signs when the source of sound is moving towards and away. 

•All steps must be shown in calculations 




• Define all questions in full as taught in the classroom.

• Copy Formula as it is. As it will account for 1 mark

• Correct substation 

•Correct answer with the correct units

• Explain fully when asked to


All the above will be checked in order for you to have a mark


The leaners will have to take note of the addition and subtraction sign on which one to use during different motions of the Source of sound.

The leaners must be able to analyze a given statement in order to make sense on what is happening.


Grade 12 Siyavula leaner Book

Grade 12 Solutions for all leaner book



Teacher Page

Name : Azola

Surname: Tyawana

Student number: 219325103