**Solution: **For the closed pipe,

Similarly, v = fλ ⇒ f = v/λ. Put in the above equation,

And for open pipe,

So f^{’} = v/λ^{’} now implies,

(11)If the amplitude of a wave is doubled, then its intensity is,

(A) Doubled | (B) Halved | (C) __ Quadrupled__ | (D) One-fourth |

**Explanation:** Intensity of a wave is proportional to the amplitude of the wave. So when the amplitude doubles, intensity is quadrupled (i-e, becomes 4 times).

12. A sound source is moving towards a stationary listener with 1/10 of the speed of the sound. The ratio of apparent to real frequency is:

(A) 11/10 | (B) (11/10)^{2} | (C) (9/10)^{2} | (D) __10/9__ |

**Solution:** The apparent frequency is given by the relation,

[See question 9 (1).]

The ratio of frequencies is, therefore,

(From the above equation)

Put the values

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