# Physics Interview Questions and Answers

In this article, we are going to learn about the Physics Interview Questions and Answers in a very detailed manner. These basic physics questions for interviews have covered are most important for interviews.

Table of Contents

## Physics Interview Questions and Answers

### Q.1 Classify the sound based on frequency.

Answer: Based on frequency, sound waves are classified as

1. Infra sound (f < 20 Hz)
2. Audible sound (20 Hz < f < 20 KHz)
3. Ultrasound (f > 20 KHz)

### Q.2 Define Music and noise. Also, give examples.

Answer: The sound that produces a pleasing effect on the ear is called musical sound. Example: Sound produced by musical instruments like sitar, violin, etc.

The sound which produces a jarring effect on the ear and is unpleasant to hear is called noise. Example: Crackers sound, road traffic, etc.

### Q.3 What is loudness? Give the relation between loudness and intensity of sound.

Answer: Loudness of a sound is the degree of sensation produced on the ear.

The relation between loudness and intensity is given by Weber-Fechner law.

L = K \log_{10} I

that is loudness is directly proportional to the logarithmic intensity of sound.

### Q.4 Define intensity level. Give its unit or define sound intensity level and write its unit.

Answer: The intensity level or relative intensity of a sound is defined as the logarithmic ratio of the intensity of a sound to standard intensity I0.

I_L = K \log_{10} (\frac{I}{I_0})

The unit of intensity level is dB.

### Q.5 Define bel and decibel.

Answer: Bel is the intensity level of a sound whose intensity is 10 times the standard intensity. One decibel is one-tenth of a bel, i.e. 1 dB = 1/10 bel.

### Q.6 What is threshold intensity? Give its value.

Answer: The minimum sound intensity that a human ear can sense is called the threshold intensity. Its value is 10-12 Wm-2.

### Q.7 What is the threshold of feeling?

Answer: The sound of intensity level 120 dB which produces a pain in the ear is called the threshold of feeling.

### Q.8 Define absorption coefficient. Give its unit.

Answer: The absorption coefficient is defined as the ratio of sound energy absorbed by a sound-absorbing material to that absorbed by an equal area of an open window.

The absorption coefficient unit is sabine or O.W.U.

### Q.9 Define reverberation time.

Answer:

Definition 1: It is defined as the time taken by a sound intensity to fall to one-millionth of its initial intensity after the source stops emitting sound.

Definition 2: It is defined as the time taken by the sound to fall below the minimum audibility level after the source stops sounding.

### Q.10 Define reverberation.

Answer: It is the persistence or prolongation of sound in a hall even though the source of sound is cut off.

### Q.11 Mention a few important conditions to be satisfied for good acoustics.

Answer:

1. The loudness of the sound should be uniform throughout the hall or auditorium either by direct system or by using a public address system.
2. The hall should have a proper reverberation time.
3. The external noises should not enter the hall or auditorium.
4. There should not be any echelon effect.

### Q.12 What are ultrasonic waves?

Answer: Sound waves having a frequency greater than 20 kHz are called ultrasonic waves.

### Q.13 Why are ultrasonics not produced by passing high-frequency alternating current through a loudspeaker?

Answer: At high frequencies, the inductive effect of a loudspeaker coil is so huge that practically no current passes through it. Moreover, the diaphragm cannot vibrate at such high frequencies.

### Q.14 Explain the magnetostriction effect. or what is the magnetostriction effect?

Answer: When a rod of ferromagnetic material like iron, cobalt, and nickel is magnetized longitudinally, the rod undergoes a small change in length. This is called the magnetostriction effect.

### Q.15 What is the piezoelectric effect?

Answer: When pressure is applied to one pair of opposite faces of crystals like quartz, tourmaline, Rochelle salt, etc., cut with their faces perpendicular to their optic axis, equal and opposite charges appear across its other faces. This is known as the piezoelectric effect.

### Q.16 What is the inverse piezoelectric effect?

Answer: If an alternating voltage is applied to one pair of opposite faces of the crystal, mechanical contractions, and expansions are produced across the other opposite faces. This phenomenon is known as the inverse piezoelectric effect.

### Q.17 Are the ultrasonic waves electromagnetic waves? Give proper reasons to support your answer.

Answer:

(a) Ultrasonic waves are not electromagnetic waves because they are sound waves.

(b) Electromagnetic waves travel with the velocity of light but ultrasonic waves travel with the velocity of sound.

Answer:

### Q.19 What are the methods of detecting ultrasonic waves?

Answer:

1. Kundt’s tube method
2. Sensitive flame method
3. Thermal methods
4. Piezo-electric method

### Q.20 What is acoustic grating?

Answer: When ultrasonic waves propagate in a liquid medium, the alternating compression and rarefactions change the density of the medium. This change in density results in a variation of the refractive index of the liquid. Under this condition, if a parallel beam of monochromatic light is passed through them at right angles to the waves, the liquid causes the light to undergo diffraction. Such a liquid column behaving like a grating is called acoustic grating.

### Q.21 What is a SONAR?

Answer:

SONAR is a device that stands for Sound Navigation and Ranging. It is based on the echo-sounding technique of ultrasounds.

It is the acoustical technique used for finding the distance and direction of submarines, depth of sea, depth of rocks in the sea, the shoal of fish in the sea, etc.

### Q.22 Expand SONAR. Give its use.

Answer: SONAR stands for SOund NAvigation and Ranging which uses highly directional ultrasonic waves to find objects and determine their distance under the sea. It is based on the principle of the echo-sounding technique of ultrasound.

### Q.23 What is the principle of SONAR?

Answer: When ultrasonic waves are transmitted through water, they get reflected by the object in the water and produce an echo signal. The distance of the object can be easily calculated by noting the time interval between the generation of the ultrasonic pulse and the reception of the echo signal.

### Q.24 How can the depth of the sea be measured using ultrasonic waves?

Answer: A pulse of ultrasonic waves is produced by the ultrasonic transducer and transmitted towards the bed of the sea. The waves reflected back from the sea bed (called echo) are collected by the receiver.

The time interval ‘t’ between the emitted signal and the received echo is measured by an oscillograph.

Knowing the velocity of sound ‘v’ through seawater, the depth of the sea ‘d’ can be calculated using the relation: d = vt/2

### Q.25 What are the applications of ultrasonics in the industry?

Answer:

• Ultrasonic waves are used to detect flaws or defects in metal structures. This is known as non-destructive testing of materials.
• Ultrasonic waves are used for material processing, that is, soldering, cutting, welding, and drilling

Hello friends, my name is Trupal Bhavsar, I am the Writer and Founder of this blog. I am Electronics Engineer(2014 pass out), Currently working as Junior Telecom Officer(B.S.N.L.) also I do Project Development, PCB designing and Teaching of Electronics Subjects.

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