What is echo?

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Jasmine Grover

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In acoustics, an echo is a reflection of sound waves off a surface back to the listener after a delay of a few seconds or more.

  • Echo is the reflection of sound reaching the listener after some time.
  • It often creates a repetitive, distorted, and sometimes amplified effect.
  • It can occur naturally in environments with hard surfaces or be deliberately created for artistic or communication purposes using specialized equipment.

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CBSE CLASS XII Related Questions

  • 1.
    What is displacement current (\( i_d \))? Considering the case of charging of a capacitor, show that \( i_d = \varepsilon_0 \frac{d\Phi_E}{dt} \). What is the value of \( i_d \) for a conductor across which a constant voltage is applied?


      • 2.
        Four independent waves are expressed as \[ (i)\; y_1=A_1\sin\omega t, \] \[ (ii)\; y_2=A_2\sin 2\omega t, \] \[ (iii)\; y_3=A_3\cos\omega t, \] \[ (iv)\; y_4=A_4\sin\left(\omega t+\frac{\pi}{3}\right) \] The interference between two of these waves is possible in

          • (i) and (iii) only
          • (iii) and (iv) only
          • (i), (iii) and (iv) only
          • All of them

        • 3.
          A square loop of side 0.50 m is placed in a uniform magnetic field of 0.4 T perpendicular to the plane of the loop. The loop is rotated through an angle of 60° in 0.2 s. The value of emf induced in the loop will be:

            • 5 V
            • 3.5 V
            • 2.5 V
            • Zero V

          • 4.
            If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.


              • 5.
                Write any two features of nuclear forces.


                  • 6.
                    Assertion (A) : The mass of a nucleus is less than the sum of the masses of the constituent nucleons. Reason (R) : Energy is absorbed when the nucleons are bound together to form a nucleus.

                      • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
                      • Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
                      • Assertion (A) is true, but Reason (R) is false.
                      • Both Assertion (A) and Reason (R) are false.
                    CBSE CLASS XII Previous Year Papers

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