MATERI FISIKA SMA KELAS 11 | GELOMBANG BUNYI | EFEK DOPPLER

Summary

In this educational video, the presenter explains the Doppler Effect in sound waves. The Doppler Effect describes how the frequency of sound changes as the source or observer moves. Through a practical example involving an ambulance, the video demonstrates how the frequency of sound heard by an observer changes when the source is moving towards or away from them. Key concepts like the Doppler Effect formula, sign conventions for moving sources and observers, and step-by-step calculations are discussed, helping viewers understand the effect and its real-world applications.

Takeaways

• 😀 The Doppler Effect is the change in frequency or wavelength of a sound wave relative to an observer, caused by the motion of the source or observer.
• 😀 The example used in the script involves an ambulance with a sound frequency of 900 Hz, where two observers, Ani and Citra, hear different frequencies.
• 😀 Ani hears a frequency of 958 Hz, while Citra hears 848.5 Hz due to the Doppler Effect.
• 😀 The Doppler Effect equation is: VP = V * (VP / (V + VS)) * FS, where VP is the observer's velocity, VS is the source velocity, and FS is the frequency of the sound source.
• 😀 The equation’s variables need to be adjusted for whether the observer or source is moving towards or away from each other.
• 😀 VP (the observer's velocity) is positive when the observer moves towards the source and negative when moving away.
• 😀 VS (the source velocity) is positive when the source moves away from the observer and negative when it moves towards the observer.
• 😀 The script explains the usage of signs for the velocity variables through a diagram with defined directions (positive for right, negative for left).
• 😀 The first example in the script calculates the frequency heard by an observer (Siti) when the ambulance is approaching and receding.
• 😀 When the ambulance approaches, the frequency heard by Siti is 987 Hz; when it recedes, the frequency is 822 Hz, giving a frequency ratio of 1.2.
• 😀 The frequency difference (Doppler shift) for Siti is 165 Hz, calculated by subtracting the frequencies heard in the two scenarios.

Q & A

What is the Doppler Effect?

The Doppler Effect is the phenomenon where there is a difference in the frequency of sound waves heard by an observer due to the motion of the source of the sound relative to the observer.

How does the frequency of sound change when the source is moving toward the observer?

When the sound source moves toward the observer, the frequency of the sound increases. This is because the sound waves are compressed as the source moves closer.

How does the frequency of sound change when the source is moving away from the observer?

When the sound source moves away from the observer, the frequency of the sound decreases. The sound waves are stretched as the source moves away.

What is the formula for the Doppler Effect?

The formula for the Doppler Effect is: VP = V * (VP / (V + Vs)) * FS, where VP is the speed of the observer, Vs is the speed of the source, FS is the frequency of the source, and V is the speed of sound in the medium.

What do the signs of the velocities (VP and Vs) represent in the Doppler Effect equation?

In the Doppler Effect equation, the velocity of the observer (VP) is positive when moving toward the source and negative when moving away. The velocity of the source (Vs) is positive when moving away from the observer and negative when moving toward the observer.

How do you determine when to use positive or negative signs in the Doppler Effect equation?

You determine the signs based on the relative direction of movement between the observer and the source. If the observer is moving toward the source, their velocity is positive, and if the source is moving toward the observer, its velocity is negative.

What are the variables involved in the Doppler Effect equation, and what do they represent?

The variables in the Doppler Effect equation are VP (speed of the observer), Vs (speed of the source), FS (frequency of the source), and V (speed of sound in the medium).

In the example involving an ambulance, what is the frequency heard by the observer when the ambulance is approaching?

When the ambulance is approaching, the frequency heard by the observer is 987 Hz.

In the example with the ambulance, what is the frequency heard by the observer when the ambulance is moving away?

When the ambulance is moving away, the frequency heard by the observer is 822 Hz.

What is the frequency shift or change when the ambulance is approaching and moving away in the example?

The frequency shift (or change) is 165 Hz, calculated as the difference between the frequency heard when the ambulance is approaching (987 Hz) and the frequency heard when the ambulance is moving away (822 Hz).