Points to remember in physics - Part 12

Points to remember in physics - Part 12

117. According to wien's law, temperature and wave length are inversely related.✔️

According to Wien's displacement law, there is an inverse relationship between the temperature of an object and the wavelength at which the object emits the maximum intensity of radiation.

Wien's displacement law is mathematically represented as:

λ_max = b / T,

where λ_max is the wavelength at which the object emits the maximum intensity of radiation, T is the temperature of the object in Kelvin, and b is Wien's displacement constant.

The constant b in the equation is approximately equal to 2.898 × 10^(-3) meters per Kelvin. It is a proportionality constant that relates the temperature and the peak wavelength of the blackbody radiation emitted by an object.

From the equation, we can see that as the temperature T increases, the wavelength λ_max at which the object emits the maximum intensity of radiation decreases. In other words, higher temperature objects emit radiation at shorter wavelengths, such as visible light or even shorter wavelengths like ultraviolet or X-rays.

Conversely, as the temperature T decreases, the wavelength λ_max at which the object emits the maximum intensity of radiation increases. Lower temperature objects emit radiation at longer wavelengths, such as infrared or even longer wavelengths like radio waves.

So, indeed, according to Wien's law, temperature and wavelength are inversely related.

118. Projectile motion of an object on earth is always parabolic.❌

Projectile motion is the motion of an object thrown into the air that only experiences the force of gravity. Its path is called its trajectory and depends on its initial speed, launch angle, and acceleration due to gravity. The object’s inertia carries it forward along a curved path. The shape of this path is a parabola.

However, this is only an idealized situation where we ignore the effects of air resistance and other forces. In reality, air resistance can significantly alter the trajectory of the motion and make it deviate from a parabola. For example, a bullet fired from a gun will experience drag force from the air that will slow it down and make it fall faster than expected. Therefore, the projectile motion of an object on Earth is not always parabolic.

119. The sum of absorption and transmission of light in a medium is equal to Incident light.❌

Absorption of light is the process by which light energy is converted into another form of energy, such as heat, by the atoms and molecules of a medium.

Transmission of light is the process by which light passes through a medium without being absorbed.

Reflection of light is the process by which light bounces off a surface.

The sum of absorption and transmission of light in a medium is equal to incident light only if there is no reflection of light.

However, most surfaces reflect some amount of light, so the sum of absorption and transmission is usually less than the incident light. The fraction of incident light that is reflected by a surface is called the reflectance. The fraction of incident light that is transmitted by a medium is called the transmittance. The fraction of incident light that is absorbed by a medium is called the absorbance.

Therefore, a more accurate statement would be that the sum of absorption, transmission and reflection of light in a medium is equal to incident light.

120. The interference of green photon to red photon will cause no effect. ❌

That’s also not entirely true. Interference of photons is the phenomenon where two or more photons combine to produce a new intensity distribution that depends on their relative phases.

Interference can occur for photons with the same or different frequencies (colors), as long as they are indistinguishable in other degrees of freedom, such as polarization, spatial mode, and temporal mode.

Interference of photons with different colors can be observed in a modified Hong-Ou-Mandel (HOM) experiment, where two photons with different frequencies enter a beam splitter that can mix photons of different energies.

The output intensity distribution will depend on the frequency difference and the phase difference between the input photons. If the frequency difference is zero, the usual HOM interference effect will occur, where the two photons will exit together in the same output port. If the frequency difference is nonzero, the interference pattern will be modulated by a sinusoidal function that depends on the frequency difference.

Therefore, the interference of green photon to red photon will cause some effect, depending on their relative phases and frequency difference.

121. Everything that moves, will eventually come to a stop. Rest is the "natural" state of all objects. ❌

The statement that "everything that moves will eventually come to a stop" is not entirely accurate. In the absence of external forces, an object in motion will continue to move with a constant velocity due to its inertia.

According to Newton's first law of motion, an object will remain in a state of uniform motion unless acted upon by a net external force.

Rest can indeed be considered a "natural" state for objects in the absence of any applied forces. If an object is at rest, it will remain at rest unless a force is applied to it. This concept is also described by Newton's first law of motion, often referred to as the law of inertia.

However, it's important to note that in the presence of external forces, objects can continue to move indefinitely or undergo changes in velocity. For example, in the vacuum of space, where there is no air resistance or other significant external forces, objects can continue moving with a constant velocity.

In the real world, objects experience various forces such as friction, air resistance, and gravitational forces, which can cause them to slow down and eventually come to a stop. These forces act as a form of resistance that opposes the object's motion and gradually dissipates its kinetic energy.

Thus, while rest may be the natural state in the absence of external forces, in the presence of such forces, objects can continue to move or eventually come to a stop depending on the circumstances.

122. The value of g is not constant. However Average value of g is a constant.✔️

The value of acceleration due to gravity, often denoted as "g," is not a constant everywhere on Earth. It can vary slightly depending on several factors such as location, altitude, and local geological conditions.

The average value of acceleration due to gravity on the surface of the Earth is approximately 9.8 meters per second squared (m/s²). This value is often used as an approximation in physics calculations and is considered a constant for most practical purposes.

However, it's important to note that the value of g can deviate slightly from this average value due to factors such as variations in Earth's gravitational field caused by differences in the distribution of mass and elevation above sea level. In different locations around the globe, the value of g can range from about 9.78 m/s² to 9.83 m/s².

For precise calculations or in more specialized contexts, local variations in the value of g may need to be taken into account. Nonetheless, for most everyday scenarios and introductory physics problems, treating the average value of g as a constant is a reasonable approximation.

123. A continuous force is needed for continuous motion ❌

In general, to sustain continuous motion, the presence of a continuous force is required. According to Newton's first law of motion, an object will remain at rest or continue moving in a straight line with a constant velocity unless acted upon by an external force.

When a force is applied to an object, it can accelerate and experience continuous motion as long as the force is present. Once the force is removed or balanced by opposing forces, the object will eventually come to a stop due to the natural tendency of objects to maintain their state of rest or uniform motion.

It's important to consider that in the absence of external forces (such as friction or air resistance), an object in motion will maintain its velocity due to its inertia. In such ideal conditions, no continuous force is needed to sustain the motion, as no external forces are acting to oppose it.

However, in most real-world situations, various forces come into play, such as friction, air resistance, or gravitational forces. These forces act as resistive or opposing forces that require a continuous application of force to maintain continuous motion.

So, while there may be instances where continuous motion can be sustained without a continuous force (in the absence of external forces), in practical scenarios, continuous motion generally necessitates the presence of a continuous force to overcome resistive forces and sustain the motion.

124. An object is hard to push because it is heavy❌

The statement that "an object is hard to push because it is heavy" is not entirely accurate. The difficulty of pushing an object is not solely determined by its weight (mass). While weight can certainly contribute to the resistance encountered when trying to move an object, it is not the only factor at play.

The difficulty of pushing or moving an object is influenced by various factors, including not only its weight but also the presence of friction and the force required to overcome inertia.

Let's consider these factors:

1. Weight: The weight of an object does affect the force required to lift or support it against the pull of gravity. However, when it comes to pushing an object horizontally on a surface, the weight alone doesn't directly determine the difficulty. It is the normal force between the object and the surface that matters. The normal force is equal in magnitude but opposite in direction to the weight, and it counteracts the weight to keep the object at rest or in equilibrium.

2. Friction: The frictional force between the object and the surface it rests on can significantly influence the difficulty of pushing. Friction opposes the relative motion between two surfaces in contact. The greater the friction, the harder it is to overcome and move the object. Factors such as the nature of the surfaces in contact and the presence of lubricants or roughness affect the frictional force.

3. Inertia: Inertia refers to an object's resistance to changes in its state of motion. When an object is at rest, it requires a greater force to overcome its inertia and initiate motion. Once in motion, the inertia of the object tends to keep it moving, requiring a smaller force to sustain the motion. The difficulty of pushing an object is influenced by its inertia, which is related to its mass.

So, while the weight of an object can contribute to the resistance encountered when pushing it, other factors such as friction and inertia also play significant roles. It's important to consider the combined effects of these factors when assessing the difficulty of pushing an object

125. There is no gravity in outer space❌

There is indeed gravity in outer space, although its effects may be different compared to what we experience on Earth's surface.

Gravity is a fundamental force of nature that exists throughout the universe. It is responsible for the attraction between objects with mass or energy. Even in the vast expanse of outer space, gravity still plays a crucial role.

In space, the force of gravity is what keeps celestial bodies like planets, moons, and stars in their orbits. It governs the motion of objects within the universe. Astronauts aboard spacecraft or at the International Space Station (ISS) also experience the effects of gravity, although they may perceive it differently due to the absence of Earth's atmosphere and other factors.

However, it is true that in certain regions of space, such as deep interstellar space, the gravitational forces between celestial bodies might be relatively weak or negligible. This can give the impression of microgravity or weightlessness. But even in these circumstances, gravitational forces still exist, albeit at reduced levels.

So, while the effects of gravity may vary depending on location and the masses involved, it is incorrect to state that there is no gravity in outer space. Gravity is a fundamental force that operates throughout the universe, shaping the motion of celestial objects and affecting the behavior of astronauts and spacecraft.

126. Planets move in circular orbits around the Sun❌

Planets do not move in perfectly circular orbits around the Sun. Instead, they follow elliptical orbits. An elliptical orbit is a slightly elongated circle, where the Sun is located at one of the two foci of the ellipse.

This understanding of planetary motion is derived from Kepler's laws of planetary motion, formulated by the astronomer Johannes Kepler in the early 17th century. Kepler's first law states that the planets orbit the Sun in elliptical paths, with the Sun at one of the foci.

In an elliptical orbit, the planet's distance from the Sun varies throughout its orbit. At the point of closest approach to the Sun (called perihelion), the planet is at its shortest distance. At the farthest point (called aphelion), it is at its greatest distance.

While the elliptical orbits of planets can appear close to circular, especially when their eccentricity (a measure of how elongated the ellipse is) is small, they are not perfectly circular. The eccentricity of a circular orbit is zero, while for an elliptical orbit, it is greater than zero.

The elliptical nature of planetary orbits helps explain various observations, such as the varying brightness of planets throughout the year and the differences in their orbital speeds at different points in their orbits.

127. Electrons orbit around the nucleus like planets orbiting the Sun❌

The idea that electrons orbit around the nucleus in a manner similar to planets orbiting the Sun is an outdated model of atomic structure. This model, known as the "planetary model" or "Rutherford-Bohr model," was proposed in the early 20th century and was a significant step in understanding atomic structure at that time.

According to the Rutherford-Bohr model, electrons were considered to be particles moving in well-defined circular orbits around the nucleus, similar to planets orbiting the Sun. However, this model had limitations and could not fully explain certain phenomena observed in atomic systems.

In modern physics, the understanding of electrons in atoms is described by quantum mechanics. According to quantum mechanics, electrons do not orbit the nucleus in classical orbits as depicted in the planetary model. Instead, electrons are described by wave functions and exist in electron clouds or orbitals that represent the probability distribution of finding an electron at a particular location around the nucleus.

The behavior of electrons is better understood through concepts such as energy levels, electron shells, and electron configurations. These concepts explain how electrons occupy specific energy levels or shells around the nucleus, and their behavior is governed by quantum mechanical principles.

In summary, while the planetary model provided a helpful conceptual framework in the early stages of atomic theory, our current understanding based on quantum mechanics suggests that electrons do not orbit the nucleus like planets orbiting the Sun. The behavior of electrons is more accurately described by their probabilistic distribution in electron clouds or orbitals.