Applied Physics Exam: Quiz!

When sound waves encounter a high tower or mountain, they bounce back and return to the source. This phenomenon is known as an echo. The reflected sound waves create a distinct repetition of the original sound, with a slight delay. This delay is due to the time it takes for the sound waves to travel to the object and back to the source. Therefore, the correct answer is echo.

When there is a relative motion between the source of sound and the observer, the apparent frequency of the sound heard by the observer is different from the actual frequency of the sound. This phenomenon is known as the Doppler effect. The Doppler effect occurs because the motion of the source or the observer causes a change in the wavelength of the sound waves. If the source is moving towards the observer, the apparent frequency will be higher than the actual frequency, and if the source is moving away from the observer, the apparent frequency will be lower than the actual frequency.

The equation v = nλ represents the relationship between velocity (v), wavelength (λ), and frequency (n) in wave propagation. This equation states that the velocity of a wave is equal to the product of its frequency and wavelength. Therefore, the given answer "v = nλ" is correct as it accurately represents this relationship.

When two waves reach a point in the same phase, it means that their crests and troughs align perfectly. This results in constructive interference, where the amplitudes of the waves add up. As a result, the intensity of the sound increases, leading to a high intensity of sound.

The given answer is correct because short radio waves are not typically in the frequency range of 1Hz to 10⁴Hz. Short radio waves are generally considered to have frequencies ranging from 3MHz to 30MHz, which is much higher than the given frequency range.

The unit watt per meter square (W/m²) is used to represent intensity. Intensity refers to the amount of energy or power per unit area. In the context of sound, intensity represents the strength or loudness of a sound wave. It is measured in watts per square meter, indicating the amount of energy passing through a given area. Therefore, intensity is the most appropriate term represented by the unit W/m².

All of the statements are true about electromagnetic waves. The wavelength range of electromagnetic waves is indeed from 10⁻⁴m to 10⁴m. They also propagate at the velocity of light. Additionally, electromagnetic waves are composed of photons. Therefore, the correct answer is "all of these."

Electromagnetic waves do not require a medium for their propagation. Unlike mechanical waves, such as longitudinal waves and elastic waves, which require a medium (such as air, water, or solids) to travel through, electromagnetic waves can travel through a vacuum, such as outer space. This is because electromagnetic waves consist of oscillating electric and magnetic fields, which can propagate through empty space without the need for a material medium.

Pitch is the property of sound that determines whether it is perceived as high or low. It is determined by the frequency of the sound wave, with higher frequencies corresponding to higher pitches and lower frequencies corresponding to lower pitches. Therefore, pitch is the property that indicates whether a sound is grave (low pitch) or shrill (high pitch). Intensity refers to the amount of energy in a sound wave, loudness refers to the perception of the sound's volume, and quality refers to the unique characteristics of a sound.

Transverse waves are characterized by particles of the medium vibrating perpendicular to the direction of propagation of the wave. In these waves, the motion of the particles is at right angles to the direction in which the wave is moving. This is in contrast to longitudinal waves, where the particles vibrate parallel to the direction of the wave. Harmonic waves refer to a specific type of wave that can be either transverse or longitudinal, so it is not the correct answer. Therefore, the correct answer is transverse waves.

Longitudinal waves are characterized by particles of the medium vibrating in the same direction as the propagation of the wave. In these waves, the displacement of particles is parallel to the direction of the wave. This is in contrast to transverse waves, where particles vibrate perpendicular to the direction of the wave. Electromagnetic waves, on the other hand, are a different type of wave that do not require a medium for propagation and consist of oscillating electric and magnetic fields. Therefore, the correct answer is longitudinal waves.

Light and heat are examples of electromagnetic waves because they both consist of oscillating electric and magnetic fields. Electromagnetic waves do not require a medium to propagate and can travel through a vacuum. They have a wide range of frequencies and wavelengths, with light being a visible form of electromagnetic radiation and heat being a form of infrared radiation.

The given question is asking which pairing is not correctly matched. The correct answer is "x-rays - harshly." This means that the association between x-rays and harshly is not accurate. It is unclear what "harshly" refers to in this context, as x-rays are typically associated with Wilhelm Conrad Roentgen, who discovered them in 1895. Therefore, the pairing of x-rays with "harshly" is incorrect.

The correct answer is "all of these." Ultrasonic waves have various applications, including sending signals, cleaning clothes and machinery parts, measuring the depth of the sea, performing ultrasonography, and removing lamp soot from chimneys.

Sound waves in air are an example of longitudinal waves because they propagate by compressing and expanding the air particles in the same direction as the wave travels. This means that the particles oscillate back and forth parallel to the direction of the wave. Other options such as waves on the surface of water, waves on strings under tension, and light waves are all examples of transverse waves, where the particles oscillate perpendicular to the direction of the wave.

The intensity of sound changes with all of these factors. The intensity of sound is inversely proportional to the square of the distance from the source, meaning that as the distance increases, the intensity decreases. The intensity is also directly proportional to the square of the amplitude, meaning that as the amplitude increases, the intensity increases. Additionally, the intensity is directly proportional to the density of the medium, meaning that as the density increases, the intensity increases. Therefore, all of these factors affect the intensity of sound.

The correct answer is "loudness ∝ log I(intensity)". This means that the loudness of a sound is directly proportional to the logarithm of its intensity. In other words, as the intensity of a sound increases, the loudness also increases, but not in a linear manner. The logarithmic relationship reflects the way our ears perceive sound, as our perception of loudness is not directly proportional to the actual physical intensity of the sound.

When a sound enters from one medium to another medium, its frequency remains constant. This means that the number of vibrations per second, which determines the pitch of the sound, does not change. However, other properties of the sound, such as its speed and wavelength, may vary depending on the characteristics of the new medium.

Waves on strings under tension are an example of transverse waves. In transverse waves, the particles of the medium vibrate perpendicular to the direction of wave propagation. In the case of waves on strings under tension, the string moves up and down (perpendicular to the direction of the wave) as the wave travels along the string. This is different from longitudinal waves, where the particles of the medium vibrate parallel to the direction of wave propagation. Waves on springs and sound waves in air are examples of longitudinal waves, not transverse waves. Therefore, the correct answer is waves on strings under tension.

When the Mach number of a body is greater than 5, it means that the body is traveling at a speed greater than five times the speed of sound in the surrounding medium. In this case, the body is said to be traveling at supersonic speeds, not ultrasonic. Ultrasonic refers to frequencies higher than the upper limit of human hearing, while supersonic refers to speeds greater than the speed of sound. Therefore, the correct statement is "none of these."

The correct answer is "all of these." This means that all of the given options (cathode rays, α-rays, canal rays, β-rays, sound waves, and ultrasonic waves) are not electromagnetic waves. Electromagnetic waves consist of oscillating electric and magnetic fields and include forms of radiation such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. However, the options listed (cathode rays, α-rays, canal rays, β-rays, sound waves, and ultrasonic waves) do not fall under the category of electromagnetic waves.

The mach number is the correct answer because it refers to the ratio of the velocity of an object to the velocity of sound in the surrounding medium. It is used to determine the speed of an object relative to the speed of sound, with a mach number greater than 1 indicating supersonic speeds. The other options, such as Doppler's effect, intensity of waves, and speed of sound, are not directly related to this specific ratio.

The unit "bel" is used to measure the intensity of sound. Intensity refers to the amount of energy that is transmitted through sound waves per unit of time and per unit of area. The bel is a logarithmic unit, and it is commonly used in acoustics to compare the loudness or strength of different sounds. It allows for a more convenient representation of the wide range of sound intensities that can be perceived by the human ear. Therefore, the correct answer is intensity of sound.

The unit of loudness is measured in "phone". The phone is a unit used to quantify the subjective loudness level of a sound. It is a logarithmic scale that represents the loudness level at a specific frequency, typically at 1 kHz. The phone scale is based on the equal loudness contours, which indicate the sound pressure levels that are perceived as equally loud by the average human ear. Therefore, the phone is the appropriate unit for measuring loudness.

The speed of sound does not depend on pressure. The speed of sound in a medium is determined by the properties of the medium itself, such as its temperature and density. Pressure, on the other hand, is a measure of the force exerted on a given area and does not directly affect the speed of sound. Therefore, the correct answer is pressure.