Applied Physics Unit-1 PDF

Subject- Applied Physicss **UNIT-1** **SOUND & HEAT** **Sound-** sound is a vibration that propagates through a medium in the form of waves. It is generated by vibrating body. The medium in which it propagates can either be a solid, liquid or gas. Sound waves are longitudinal waves. This means...

Subject- Applied Physicss **UNIT-1** **SOUND & HEAT** **Sound-** sound is a vibration that propagates through a medium in the form of waves. It is generated by vibrating body. The medium in which it propagates can either be a solid, liquid or gas. Sound waves are longitudinal waves. This means that the propagation of vibration of particles is parallel to the energy propagation direction. When the atoms are set in vibration they move back and forth. This continuous back-and-forth motion results in a high-pressure and low-pressure region in the medium. This high-pressure and low-pressure region is termed as **compression** and **rarefaction**. These regions are transported to the surrounding medium resulting in the sound waves travelling from one medium to another medium. **Nature of sound waves** The sound waves produce by different source have different characteristics. Example- the sound produced by a guitar is different from the sound produced by drum. Sound can be characterized by its frequency wavelength and amplitude. **Frequency of sound wave-** The number of rarefaction and compression that occurs per unit time is known as frequency of a sound wave. The formula of the frequency of a wave is given as: F=1/T Where f is the frequency of sound wave The frequency range for the human ear is 20Hz-20,000Hz. **Wavelength of sound wave-**  The disturbance between the successive compression and rarefaction is known as wavelength of sound wave. The formula for the wavelength of sound wave is given as: λ=v/F where F is the frequency of sound wave v is the velocity of sound wave **Amplitude of sound wave-** the amplitude of sound wave is the magnitude of maximum disturbance in a sound wave. Higher the amplitude higher the energy in sound wave. **Speed of sound wave-** The speed at which sound wave propagates through a medium is known as the speed of sound. The speed of sound is different in different media. The speed of sound is highest in solid because the atoms in solid are highly compressed. **C=d/t** Where d is the distance travelled by sound t is the time taken to cover the distance **Medium** **Speed of sound** -------------- -------------------- Water 1481 m/s Air 343.2 m/s Metal 4600 m/s Glass 4540 m/s Soft tissues 1540 m/s **Reflection of sound-** Reflection of sound is similar to the reflection of light. The reflection of sound obeys the following laws of reflection- The angle of incident is equal to the angle of reflection. The incident sound and the normal sound all lie in the same plane. NCERT Class 9 Science Lab Manual - Sound - CBSE Tuts **Interference-** Interference is the phenomenon in which two or more waves superpose to form a resultant wave of greater, lower, or the same amplitude. There are two types of interference A. Constructive Interference B. Destructive Interference **Constructive Interference-** When two waves of same phases meet, their resultant amplitude increased is called constructive interference. **Destructive interference-** When two waves of different phases meet, their resultant amplitude decreases is called destructive interference. The resultant amplitude of the wave, which undergoes destructive interference is equal to the difference in the individual amplitudes of the waves.  **Ultrasonic waves-** Ultrasound waves are sound waves whose frequencies are higher than those waves normally audible to humans (i.e. from 20 Hz -20,000Hz). Ultrasonic waves are used in the detection. **Production of ultrasonic waves-** 1\. Piezoelectric crystal -Inside the ultrasound probe there is a piezoelectric crystal. This crystal has a unique property, it can change its shape when an electrical voltage is applied to it. 2\. Electric Voltage -- When an electric voltage is applied to the piezoelectric crystal, it undergoes rapid expansion and contraction due to the inverse piezoelectric effect. This rapid movement generates high-frequency sound waves. 3\. Sound wave Emission -- These sound waves are typically in the ultrasonic range, meaning they have a frequency higher than what the human ear can hear. The crystal emits these waves as a focused beam into the body. 4\. Body interaction -- These ultrasonic waves travel into the body, and when they encounter different tissues with varying intensities, some of the waves are reflected back to the transducer. 5\. Echo Reception -- the same piezoelectric crystal now acts as a receiver. It detects the reflected waves(echoes) as they return to the probe. 6\. Data Analysis -- the time it takes for the echoes to return and strength provides information about the depth, size, and density of the structure inside the body. 7\. Image formation -- a computer processes this data and forms a 2D and 3D image on the ultrasound machines screen. **Doppler's effect-** The **Doppler effect** or **Doppler shift** (or simply **Doppler**) is the apparent change in [frequency](https://en.wikipedia.org/wiki/Frequency) of a [wave](https://en.wikipedia.org/wiki/Wave) in relation to an [observer](https://en.wikipedia.org/wiki/Observer_(physics)) moving relative to the wave source.  It is named after the [Austrian](https://en.wikipedia.org/wiki/Austria) physicist [Christian Doppler](https://en.wikipedia.org/wiki/Christian_Doppler), who described the phenomenon in 1842. Example- It is similar to a siren on a fire truck; the sound is high pitched as the truck approaches the listener (λ is compressed), and shifted to a lower pitch as it moves away from the listener (λ is expanded) Doppler Effect Demonstrations and Animations **Doppler ultrasound-** Comparison of incident US frequency with the reflected US frequency from the blood cells, gives the velocity of blood. It also helps measurement of blood flow (indirect), create color blood flow maps of vasculature, etc. The change of frequency is proportional to the velocity of the interface. Higher the transducer frequency or faster the interface moves, greater the change in frequency. A doppler ultrasound can help to determine the blood pressure in your arteries. **[HEAT ]** Heat is a form of internal energy, which can be transferred from one part of the body to another. Eg. - If a hot body and a cold body are placed in close contact, the hot body will transfer some of its heat energy to the cold body until the temperature of the two become equal. There are three methods of heat transfer, namely, conduction, convection and radiation. **Conduction-** It is the process in which heat energy is transferred by collisions between neighbouring atoms, without the visible motion of the particles. Conduction takes place in solids, liquids and gases.  **Convection-** It is the process in which heat energy is transferred by the actual motion of the particles of the body. Heat in liquid causes the fluid to expand and making it less dense and starts rising. Convection takes place in liquids and gases. **Radiation-** It is the process by which heat energy is transmitted from one place to another without the aid of any material medium. When a body has internal energy, its atoms and molecules vibrate and emits electromagnetic radiation, which can transport energy across a vacuum, e.g. heat reaches the earth from the sun **Heat capacity-** The heat capacity of a material is the heat required to raise its temperature by 1 K. It is independent of material size or shape and expressed in JK--1. **Specific heat capacity** The heat required to raise the temperature of a 1 kg material by 1K is called specific heat capacity, and it is expressed in Jkg--1 K--1. **Thermal conductivity-** Thermal conductivity refers to the ability of a given material to conduct/transfer heat. It is generally denoted by the symbol 'k' but can also be denoted by 'λ' and 'κ'. The reciprocal of this quantity is known as thermal resistivity. **K = (QL)/(AΔT)** Where - K is the thermal conductivity in W/m.K - Q is the amount of heat transferred through the material in Joules/second or Watts - L is the distance between the two isothermal planes - A is the area of the surface in square meters - ΔT is the difference in temperature in Kelvin Metals in general are good conductors of heat, e.g. silver, copper, etc. Nonmetals are bad conductors of heat, e.g. glass, rubber, wood, etc. What is thermal conductivity? (article) \| Khan Academy **Thermal expansion** refers to the phenomenon where materials, such as solids, liquids, and gases, increase in size (expand) when they are heated and decrease in size (contract) when they are cooled. This occurs because the particles that make up these materials gain or lose kinetic energy as their temperature changes. Key points about thermal expansion include: 1. **Linear Expansion:** In the case of solids, there are different types of thermal expansion. Linear expansion refers to the increase in length of a solid material when heated or its decrease in length when cooled. 2. **Volume Expansion**: For most materials, not only do they expand in length but also in volume when heated. The coefficient of volume expansion (β) is used to describe this property. 3. *Area expansion* occurs is the change in area due to temperature change.  4. **Application**s: Understanding thermal expansion is crucial in engineering and construction. It is considered when designing structures, pipelines, and any component that experiences temperature variations. Engineers must account for the expansion and contraction of materials to prevent damage or structural failure due to temperature changes. 5. **Examples**: Common examples of thermal expansion include the expansion of railroad tracks on hot days, the expansion of metals in thermostats to control temperature, the cracking of pavement due to temperature changes, and the use of expansion joints in buildings to allow for movement caused by temperature fluctuations. 6. **Anomalous Expansion**: While most materials expand when heated, some substances, like water, exhibit anomalous behavior. Water expands as it is heated from freezing temperatures to around 4 degrees Celsius and then contracts as it is heated further. This unique behavior is a result of the structure of water molecules. **Temperature**- the measure of hotness or coldness expressed in terms of any of several [arbitrary](https://www.britannica.com/dictionary/arbitrary) scales and indicating the direction in which [heat](https://www.britannica.com/science/heat) [energy](https://www.britannica.com/science/energy) will spontaneously flow---i.e., from a hotter body (one at a higher temperature) to a colder body (one at a lower temperature). Three temperature scales are in general use today. - **The [Fahrenheit (°F) temperature scale](https://www.britannica.com/science/Fahrenheit-temperature-scale)** is used in the [United States](https://www.britannica.com/place/United-States) and a few other English-speaking countries. - **The [Celsius (°C) temperature scale](https://www.britannica.com/technology/Celsius-temperature-scale)** is standard in virtually all countries that have adopted the [metric system](https://www.britannica.com/science/metric-system-measurement) of measurement, and it is widely used in the sciences. - **The [Kelvin (K) scale](https://www.britannica.com/science/kelvin)**, an [absolute temperature scale](https://www.britannica.com/science/absolute-temperature-scale) (obtained by shifting the Celsius scale by −273.15° so that [absolute zero](https://www.britannica.com/science/absolute-zero) coincides with 0 K), is recognized as the international standard for scientific temperature measurement. **Newton's Law of Cooling** According to Newton's law of cooling, the rate of loss of heat from a body is directly proportional to the difference in the temperature of the body and its surroundings. Newton's law of cooling is given by, dT/dt = k(T~t~ -- T~s~) Where, - T~t~ = Temperature of the body at time t - T~s~ = Temperature of the surrounding - k = Positive constant that depends on the area and nature of the surface of the body under consideration. Limitations of Newton's Law of Cooling -------------------------------------- - The difference in temperature between the body and surroundings must be small - The loss of heat from the body should be by [radiation](https://byjus.com/jee/radiation/) only - The major limitation of Newton's law of cooling is that the temperature of the surroundings must remain constant during the cooling of the body **Heat radiation:-** Heat radiation, also known as thermal radiation, is a form of electromagnetic radiation that is emitted by any object with a temperature above absolute zero (0 Kelvin or -273.15 degrees Celsius). Heat radiation does not require a medium (such as air or a solid) to transfer heat; it can travel through a vacuum, which makes it different from conduction and convection. Here are some key characteristics and principles of heat radiation: 1. **Electromagnetic Waves**: Heat radiation consists of electromagnetic waves, just like light, radio waves, and microwaves. 2. **Emissivity:** The ability of an object to emit heat radiation depends on its surface properties and its emissivity. Emissivity is a measure of how efficiently an object emits radiation relative to a perfect blackbody (an idealized object that absorbs and emits all radiation). A perfect blackbody has an emissivity of 1, while real-world objects have emissivities less than 1. 3. **Heat Absorption and Emission**: Objects can absorb and emit heat radiation. When an object absorbs more radiation than it emits, its temperature increases. Conversely, when it emits more radiation than it absorbs, its temperature decreases. 4. Applications: Heat radiation has various practical applications, including in heating systems (radiators and heating coils), cooking (microwaves and ovens), thermography (thermal imaging cameras), and in space science (studying celestial objects and the cosmic microwave background radiation).