What is the minimum distance required to hear a distinct echo? (Assuming speed of sound in air is 344 m/s)
A. 17.2 meters
B. 34.4 meters
C. 25.6 meters
D. 10 meters
Answer: Option A
Solution (By JKSSB Mock Tests)
The human ear retains the sensation of sound for about 0.1 seconds (persistence of hearing). To hear a distinct echo, the reflected sound must reach the ear after at least 0.1 s. Distance traveled by sound = Speed × Time = 344 m/s × 0.1 s = 34.4 m. Since this is the total distance (go and return), the minimum distance to the obstacle is 34.4 / 2 = 17.2 meters.
Explanation:
The formula for capacitors in series is exactly the opposite of resistors. 1/C_eq = 1/C1 + 1/C2 + 1/C3. Here, all are 3 uF. So, 1/C_eq = 1/3 + 1/3 + 1/3 = 3/3 = 1. Therefore, C_eq = 1 microfarad. When identical capacitors are in series, you simply divide the capacitance by the number of capacitors (3/3 = 1).
Explanation:
Ionosphere contains ions and free electrons, reflects radio waves back to Earth, enabling long-distance radio communication. Used in skywave propagation. Troposphere weather layer.
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