Two persons A and B are standing in front of a cliff in the same line, 170 m apart, as shown in the diagram.

Person B fires a gun and hears the echo in 3 s. Then person A, standing in front of B, fires the gun. (Speed of sound in air = 340 m s⁻¹)

(a) Calculate: (1) the distance of B from the cliff; (2) the minimum time in which B hears the gunshot fired by A.

(b) Fill in the blank: The echo is softer than the original sound due to the decrease in …………… [amplitude / frequency] of the wave.

Three cylindrical jars A, B and C contain equal volumes of water up to different heights. Their radii satisfy rB < rA < rC. Which jar produces the shrillest sound when air is blown across its mouth? (a) A (b) B (c) C (d) All produce the same sound

Complete the following by choosing the correct answers from the bracket: (a) A car is moving in uniform circular motion. The direction of friction between the tyres and the path is ............... [towards the centre / tangential to the path]. (b) When a ray of light passes from a denser to a rarer medium, its wavelength ............... [decreases / increases]. (c) The lid of a calorimeter minimises heat loss by ............... [convection / radiation]. (d) Quality of sound depends on its ............... [amplitude / waveform]. (e) A substance whose resistance becomes almost negligible at a temperature near absolute zero is called a ............... [semiconductor / superconductor]. (f) ............... radiation deviates minimum in a magnetic field [Alpha / Beta].

(a) Define natural vibrations. (b) How is this vibration different from damped vibrations in terms of their amplitudes?

(a) One end of a plastic foot ruler is held tightly at the edge of a table and the other end is plucked. Name the vibrations produced in the ruler. (b) Now the ruler is pushed inside partially and plucked again from its free end. State with a reason whether the frequency of vibration increases or decreases.

We are able to see the T.V. channels clearly when we set T.V. on auto-tuning. (a) Which phenomenon led to the clear visibility of the channels, due to auto tuning? (b) Define the above phenomenon mentioned by you. (c) Give any one more example of this phenomenon.

The diagrams given below show two sound boxes A and B with wires of the same length (l) and tension (10 kgf) but different cross-sectional areas. Simultaneously, vibrating tuning forks of frequency 300 Hz are placed on boxes A and B. The paper rider falls off in case of B but not in case of A. (a) Name and explain the phenomenon responsible for the falling off of the paper rider in B. (b) The wire A resonates with a tuning fork of frequency ‘f’. Is ‘f’ greater than, less than or equal to 300 Hz? Justify your answer.

Rohan conducted experiments on echo in different media. He observed that a minimum distance of ‘x’ meters is required for the echo to be heard in oxygen and ‘y’ meters in benzene. Compare ‘x’ and ‘y’. Justify your answer. Speed of sound in oxygen: 340 ms-1 Speed of sound in benzene: 200 ms-1

(a) Which characteristic of sound is affected due to the larger surface of a school bell? (b) Calculate the distance covered by the Ultrasonic wave having a velocity of 1.5 km s⁻¹ in 14 s, when it is received after reflection by the receiver of the SONAR.

When the stem of a vibrating tuning fork is pressed on a table, the tabletop starts vibrating. These vibrations are definitely an example of: (a) resonance (b) natural vibrations (c) forced vibrations (d) damped vibrations

The displacement–time graph of a sound wave produced by a vibrating wire is shown below. (a) How will you adjust the tension in the wire, to reduce the length of PR? (b) Which characteristic of sound is affected by the reduction in the length of PR?

A metal foot ruler is held at the edge of a table. It is pressed at its free end and then released. It vibrates. (a) Name the vibrations produced. (b) State one way to increase the frequency of these vibrations.

Two notes are produced from two different musical instruments, such that they have same loudness and same pitch. The produced notes differ in their: (a) Waveform (b) Frequency (c) Wavelength (d) Speed