Page 133 - Physics - XI

Q2. What is resonance?
Ans. The phenomenon of setting one body into vibrations with its natural frequency with the help of
another body vibrating with the same frequency is called resonance.

Q3. What will be the shape of graphs plotted between: (i) n and 1/l (ii) n and T (iii) l and T?
2
2
Ans. All will be straight lines.
Q4. What is a tuning fork?
Ans. It is a metallic rod bent into U-shape and having a heavy stem attached to the middle of the bent
portion.

Q5. Why are there some holes in a wooden box?
Ans. So that internal air and external air may have a direct contact.
Q6. Why does string of a sonometer vibrate?
Ans. When the vibrating tuning fork is kept on the board of a sonometer, the forced vibrations of the

board communicate energy to string which in turn is set into forced vibrations.
Q7. What is the function of a paper rider?

Ans. Paper rider placed at the middle point is thrown off (antinode) where the amplitude is maximum
when resonance is obtained.
Q8. Why do you start from the minimum length of the wire?
Ans. To make sure that the wire vibrates in the fundamental mode, i.e. wire vibrates making only one
segment or loop.

Q9. What do you mean by unison?
Ans. Two notes are said to be in unison if they have the same frequency.

Q10. What is the natural frequency of a sonometer wire under tension?
Ans. The expression for natural frequency n of a sonometer wire vibrating in one loop is given as

n = 1 T
2l m
where T is the tension, m is the mass per unit length, and l is the resonant length of the wire.

Q11. State the law of mass.

Ans. It is given as v ∝ 1 , when l and T are constant.
m

Q12. State the law of mass and law of diameter.
1 1
Ans. According to the law of mass, v ∝ and according to the law of diameter, v ∝
m D
Q13. What is the principle of superposition of waves? (NCERT)
Ans. According to the principle of superposition of waves, the resultant displacement of a particle is
equal to the vector sum of the individual displacements given to it by superposing waves.

Q14. What are stationary waves? (NCERT)
Ans. Superposition of two waves of same frequency and same amplitude and travelling with same
velocity in opposite direction produce stationary waves.

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