NSC Physical Sciences Doppler Effect: STATE the Doppler effect in word

STATE the Doppler effect in words - NSC Physical Sciences - Question 6 - 2020 - Paper 1

Question 6

STATE the Doppler effect in words. Does the detector record the frequency of 3 148 Hz when the train moves TOWARDS the detector or AWAY from the detector? Calculat... show full transcript

Worked Solution & Example Answer:STATE the Doppler effect in words - NSC Physical Sciences - Question 6 - 2020 - Paper 1

Step 1

State the Doppler effect in words.

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Answer

The Doppler effect is the change in frequency (or pitch) of a wave in relation to an observer moving relative to the wave source. It occurs because the source of the sound and the observer are in relative motion, leading to an observed change in frequency depending on whether the source is moving towards or away from the listener.

Step 2

Does the detector record the frequency of 3 148 Hz when the train moves TOWARDS the detector or AWAY from the detector?

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Answer

The detector records the frequency of 3 148 Hz when the train moves TOWARDS the detector.

Step 3

Calculate the speed of the train. Take the speed of sound in air as 340 m s⁻¹.

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Answer

To find the speed of the train, we can use the Doppler effect formula. When the source is moving towards the observer:

$f' = \frac{v + v_s}{v - v_o} f$

Where:

$f' = 3 148 Hz$ (observed frequency)
$f = 2 073 Hz$ (actual frequency)
$v = 340 m/s$ (speed of sound)
$v_s$ = speed of the source (train)
$v_o = 0$ (observer is stationary)

Rearranging the equation:

$v_s = \frac{f' v - f v}{f'}$

Substituting the known values:

$v_s = \frac{3148 \times 340 - 2073 \times 340}{3148}$

Calculating gives:

$v_s = 70 \text{ m/s}$

Step 4

The detector started recording the frequency of the moving train's siren when the train was 350 m away.

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Answer

To calculate time t₁ indicated on the graph, we can use the formula:

$t = \frac{d}{v_s}$

Where:

$d = 350 m$ (distance from the detector)
$v_s = 70 m/s$ (speed of the train)

Calculating gives:

$t_1 = \frac{350}{70} = 5 \text{ s}$

STATE the Doppler effect in words - NSC Physical Sciences - Question 6 - 2020 - Paper 1

Worked Solution & Example Answer:STATE the Doppler effect in words - NSC Physical Sciences - Question 6 - 2020 - Paper 1

State the Doppler effect in words.

Does the detector record the frequency of 3 148 Hz when the train moves TOWARDS the detector or AWAY from the detector?

Calculate the speed of the train. Take the speed of sound in air as 340 m s⁻¹.

The detector started recording the frequency of the moving train's siren when the train was 350 m away.

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