Normal Modes of a String

Author:D. C. Pandey
JEE Advanced
IMPORTANT

Important Questions on Normal Modes of a String

EASY
IMPORTANT

Two pulses of identical shape overlap such that the displacement of the rope is momentarily zero at all points. What happens to the energy at this time?

EASY
IMPORTANT

A string fastened at both ends has successive resonances with wavelengths of 0.54 m for the nth harmonic and 0.48 m for the (n+1)th harmonic.
(a) Which harmonics are these?
(b) What is the length of the string?
(c) What is the wavelength of the fundamental frequency?

EASY
IMPORTANT

A 160 g rope 4 m long is fixed at one end and tied to a light string of the same length at the other end. Its tension is 400 N.
(a) What are the wavelengths of the fundamental and the first two overtones?
(b) What are the frequencies of these standing waves?
[Note: In this case, fixed end is a node and the end tied with the light string is antinode.]

EASY
IMPORTANT

Figure shows different standing wave patterns on a string of linear mass density 4.0×10-2 kg m-1 under a tension of 100 N. The amplitude of antinodes is indicated in each figure. The length of the string is 2.0 m.

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(i) Obtain the frequencies of the modes shown in figures (a) and (b).
(ii) Write down the transverse displacement y as a function of x and t for each mode. (Take the initial configuration of the wire in each mode to be as shown by the dark lines in the figure).

HARD
IMPORTANT

A wire with mass 40.0 g is stretched so that its ends are tied down at points 80.0 cm apart. The wire vibrates in its fundamental mode with frequency 60.0 Hz and with an amplitude at the antinodes of 0.300 cm.
(a) What is the speed of propagation of transverse wave in the wire?
(b) Compute the tension in the wire.
(c) Find the maximum transverse velocity and acceleration of particles in the wire.

MEDIUM
IMPORTANT

A 1.50 m long rope is stretched between two supports with a tension that makes the speed of transverse waves 48.0 m s-1. What are the wavelength and frequency of
(a) the fundamental?
(b) the second overtone?
(c) the fourth harmonic?

EASY
IMPORTANT

A guitar string is 90 cm long and has a fundamental frequency of 124 Hz. Where should it be pressed to produce a fundamental frequency of 186 Hz?

EASY
IMPORTANT

A sonometer wire has a total length of 1 m between the fixed ends. Where should the two bridges be placed below the wire so that the three segments of the wire have their fundamental frequencies in the ratio 1:2:3?

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IMPORTANT

A string vibrates in 4 segments to a frequency of 400 Hz.
(a) What is its fundamental frequency?
(b) What frequency will cause it to vibrate into 7 segments?

EASY
IMPORTANT

The vibrations from an 800 Hz tuning fork set up standing waves in a string clamped at both ends. The wave speed in the string is known to be 400 m s-1 for the tension used. The standing wave is observed to have four antinodes. How long is the string?

HARD
IMPORTANT

A wire having a linear density of 0.05 g cm-1 is stretched between two rigid supports with a tension of 450 N. It is observed that the wire resonates at a frequency of 420 Hz. The next higher frequency at which the same wire resonates is 490 Hz. Find the length of the wire.

MEDIUM
IMPORTANT

A 60.0 cm guitar string under a tension of 50.0 N has a mass per unit length of 0.100 g cm-1 What is the highest resonance frequency of the string that can be heard by a person able to hear frequencies upto 20000 Hz ?

MEDIUM
IMPORTANT

A string vibrates in its first normal mode with a frequency of 220 vibrations s-1. The vibrating segment is 70.0 cm long and has a mass of 1.20 g.
(a) Find the tension in the string.
(b) Determine the frequency of vibration, when the string vibrates in three segments.

MEDIUM
IMPORTANT

Find the fundamental frequency and the next three frequencies that could cause a standing wave pattern on a string that is 30.0 m long has a mass per unit length of  9.00×10-3 kg m-1 and is stretched to a tension of 20.0 N.

MEDIUM
IMPORTANT

The period of oscillations of a point is 0.04 s and the velocity of propagation of oscillation is 300 m s-1. The difference of phases between the oscillations of two points at distance 10 m and 16 m, respectively, from the source of oscillations is

MEDIUM
IMPORTANT

Three resonant frequencies of string with both rigid ends are 90,150 and 210 Hz. If the length of the string is 80 cm, what is the speed of the transverse wave in the string?

MEDIUM
IMPORTANT

For a certain stretched string, three consecutive resonance frequencies are observed as 105, 175 and 245 Hz, respectively. Then, the fundamental frequency is

EASY
IMPORTANT

If λ1, λ2 and λ3 are the wavelength of the waves giving resonance to the fundamental, first and second overtone modes, respectively, in a string fixed at both ends. The ratio of the wavelengths λ1:λ2:λ3 is

HARD
IMPORTANT

A light string is tied at one end to fixed support and to a heavy string of equal length L at the other end as shown in figure. Mass per unit length of the strings are μ and 9μ and the tension is T. Find the possible values of frequencies such that point A is a node/antinode.

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HARD
IMPORTANT

Three pieces of string, each of length L, are joined together end-to-end, to make a combined string of length 3L. The first piece of string has a mass per unit length μ1, the second piece has a mass per unit length μ2=4μ1 and the third piece has a mass per unit length μ3=μ1/4 

(a) If the combined string is under tension F, how much time does it take a transverse wave to travel the entire length 3L ? Give your answer in terms of L, F and μ1.
(b) Does your answer to part (a) depend on the order in which the three pieces are ioined together? Explain.