Tag: physics

Questions Related to physics

A string is under tension so that its length is increased by $1/n$ times its original length. The ratio of fundamental frequency of longitudinal vibrations and transverse vibrations will be

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. $1:n$

  2. ${n}^{2}:1$

  3. $\sqrt{n}:1$

  4. $n:n+1$

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Correct Option: D

Motion that moves to and fro in regular time intervals is called _________________ motion.

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. Vibratory

  2. Translatory

  3. Rotatory

  4. Accelerating

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Correct Option: A
Explanation:

Sounds are made by vibrations. Some vibrations are easy to see. The vibrations that create sound must travel through a medium, such as air or water, or anything made of molecules. With each forward motion, air molecules pulse outward, pushing other air molecules and crowding them together. With each backward motion, the molecules get less crowded. The forward and backward vibration of the glass creates a chain reaction of crowded and not-so-crowded molecules that ripples through the air. This traveling vibration is called a sound wave. 
Motion that moves to and fro in regular time intervals is called vibratory or oscillatory motion.

When we hear a sound, we can identify its source from : 

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. Amplitude of sound

  2. Intensity of sound

  3. Wavelength of sound

  4. Overtones present in the sound

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Correct Option: D
Explanation:

Answer is D.

When we hear a sound, we can identify its source from overtones present in the sound.
The fundamental is the frequency at which the entire wave vibrates. Overtones are other sinusoidal components present at frequencies above the fundamental. All of the frequency components that make up the total waveform, including the fundamental and the overtones, are called partials. Together they form the harmonic series.
Overtones which are perfect integer multiples of the fundamental are called harmonics. When an overtone is near to being harmonic, but not exact, it is sometimes called a harmonic partial, although they are often referred to simply as harmonics. Sometimes overtones are created that are not anywhere near a harmonic, and are just called partials or inharmonic overtones.

The vibrations produced by the body after it is into vibration is called ....................

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. Force Vibrations

  2. Free or Natural Vibrations

  3. Damped Vibrations

  4. None of these

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Correct Option: B

The length of a stretched string is $2 m$. The tension in it and its mass are $10 N$ and $0.80 kg$ respectively. Arrange the following steps in a sequence to find the third harmonic of transverse wave that can be created in the string.
(a) Find the linear mass density ($m$) using the formula, $m$ $\displaystyle = \dfrac{mass (M)  of \ the \  string}{length (l)  of \ the \  string}$
(b) Collect the data from the problem and find the length($l$) tenstion ($T$) and mass ($M$) of the stretched string.
(c) The fundamental frequency of a stretched vibrating string is given by $n$ $=\displaystyle \dfrac{1}{2l} \sqrt{\dfrac{T}{m}}$
(d) The frequency of $2^{nd}$ overtone or $3^{rd}$ harmonic is given by $n _2\displaystyle = \dfrac{3}{2l}\sqrt{\dfrac{T}{m}}=3n$.

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. a b c d

  2. d b c a

  3. b a c d

  4. b d c a

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Correct Option: C
Explanation:

Collect the data from the problem and find the length ($l$), tension ($T$) and mass ($M$) of the stretched string (b). 

Find the linear mass density (m) using the formula, m $= m/l$  (a).
The fundamental frequency of a stretched vibrating string is given by, n $=\displaystyle \dfrac{1}{2l} \sqrt{\dfrac{T}{m}}$ (c).
The frequency of $2^{nd}$ overtone or $3^{rd}$ harmonic is given by $n _2=\displaystyle \dfrac{3}{2l} \sqrt{\dfrac{T}{m}}=3n$ (d)

All overtones are stationary wave.

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. True

  2. False

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Correct Option: B
Explanation:

All overtones are not stationary waves. Only those overtones which match the frequencies of the harmonics act as stationary waves.

All harmonics in a stringed instrument are

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. Standing waves

  2. Progressive wave

  3. Electromagnetic waves

  4. Transverse waves

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Correct Option: A
Explanation:

All harmonics in a stringed instrument are stationary or standing waves

The correct option is (a)

nth overtone and (n/2) harmonic are always equal

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. True

  2. False

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Correct Option: B
Explanation:

$n^{th}$ overtone is always equal to (n+1) harmonic.

For example :
First overtone = second overtone 
Second overtone = third overtone 

All harmonics are possible in a string fixed at one end

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. True

  2. False

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Correct Option: B
Explanation:

In a string fixed at one end, only odd harmonics are allowed

A set of 3 standing waves 5, 10 and 15 Hz are to be setup on a string fixed at one end. One of these frequencies are suppressed, while passing through it. Identify them:

physics oscillations and waves standing waves in strings standing waves reflection of waves

  1. 5 Hz

  2. 10 Hz

  3. 15 Hz

  4. All the frequencies will pass through them

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Correct Option: B
Explanation:

In a string fixed at one end, only odd harmonics are allowed and even harmonics are suppressed.

Thus the 10Hz standing wave is suppressed,
The correct option is (b)