iGCSE Physics (0625) 3.4 Sound-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
An echo is the reflection of sound. To hear an echo, the sound must travel from the student to the wall and back again.
If the distance to the wall is $d$, the total distance travelled by the sound is $2d$.
Using the formula for speed, $v = \frac{\text{total distance}}{\text{time}}$, we have $v = \frac{2d}{t}$.
Rearranging to find the distance between the student and the wall: $2d = v \times t$.
Therefore, $d = \frac{v \times t}{2}$, which is expressed as $(v \times t) \div 2$.
This matches Option C.
▶️ Answer/Explanation
Detailed solution:
Sound is a longitudinal wave consisting of oscillations in the medium’s pressure and density.
A compression is a region where the particles are pushed closer together, resulting in high pressure and a higher density ($\rho$).
Conversely, a rarefaction is a region where the particles are spread further apart, leading to low pressure and a lower density.
Wavelength ($\lambda$) is defined as the distance between two successive compressions or rarefactions, not a property of a single region.
Thus, the density of air is greater in a compression than in a rarefaction, making option C the correct choice.
▶️ Answer/Explanation
Detailed solution:
The loudness of a sound wave is determined by its amplitude; a decrease in amplitude results in a quieter sound.
The pitch of a sound is determined by its frequency, where f= T 1 .
When the frequency decreases, the number of vibrations per second is lower, resulting in a lower pitch.
Since the question states both properties decrease, the sound becomes both quieter and lower in pitch.
This corresponds exactly to the description provided in Option D.
Therefore, the observed change is a quieter sound with a lower pitch.