Solved: PHYSICS Question for NEET

NEET PHYSICSEasy

Sound waves travel at $350 \text{ m/s}$ through warm air and at $3500 \text{ m/s}$ through brass. The wavelength of a $700 \text{ Hz}$ acoustic wave as it enters brass from warm air:

increases by factor 20

increases by factor 10

decreases by factor 20

decreases by factor 10

Step-by-Step Solution

Identify the Constant Property: When a wave passes from one medium to another (e.g., from air to brass), its frequency ( $f$ ) remains constant.
Relate Wavelength and Speed: The speed of a wave is given by the formula $v = f\lambda$ . Since the frequency $f$ is constant, the wavelength $\lambda$ is directly proportional to the wave speed $v$ (i.e., $\lambda \propto v$ ).
Calculate the Ratio: We can find the change in wavelength by taking the ratio of the speeds in the two media: $\frac{\lambda_{\text{brass}}}{\lambda_{\text{air}}} = \frac{v_{\text{brass}}}{v_{\text{air}}}$ $\frac{\lambda_{\text{brass}}}{\lambda_{\text{air}}} = \frac{3500 \text{ m/s}}{350 \text{ m/s}} = 10$
Conclusion: The wavelength in brass is 10 times the wavelength in air. Therefore, the wavelength increases by a factor of 10.

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