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].

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.

(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.

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

When a body vibrates under a periodic force, the vibrations of the body are always: (a) natural vibrations (b) damped vibrations (c) forced vibrations (d) resonant vibrations

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

Assertion (A) : As the level of water in a tall measuring cylinder kept under running tap rises, the pitch of sound gradually increases. Reason (R) : Frequency of sound is inversely proportional to the length of the water column. (a) Both (A) and (R) are true and (R) is correct explanation of (A). (b) Both (A) and (R) are true and (R) is not the correct explanation of (A). (c) (A) is true but (R) is false. (d) (A) is false but (R) is true.

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) 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.

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.

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