Points to remember in Physics - Part 5

Points to remember in Physics - Part 5

41. Projectile motion does not depend upon mass

Projectile motion is the motion of an object that is launched into the air and then moves under the influence of gravity. The path of the object can be described as a parabolic curve. 

The motion of a projectile is governed by the laws of physics, including Newton's laws of motion and the law of conservation of energy. According to these laws, the mass of an object does not affect its motion in a vacuum (i.e. in the absence of air resistance). Therefore, the motion of a projectile, such as a ball or a bullet, does not depend on its mass.

However, in the presence of air resistance, the motion of a projectile can be affected by its mass. This is because air resistance is a force that opposes motion and is proportional to the surface area and velocity of the object. Therefore, a larger and heavier object would experience more air resistance than a smaller and lighter object, which would affect its motion.

42. Power remains unchanged in the transformer

Actually, power is not exactly "unchanged" in a transformer. A transformer is an electrical device that is used to transfer electrical energy from one circuit to another through electromagnetic induction. 

In a transformer, the power that is transferred is equal to the input power, but the voltage and current levels can be changed. 

The power in a transformer is calculated using the equation P = VI, where V is the voltage and I is the current. In a transformer, the voltage and current on the input side (the primary) are related to the voltage and current on the output side (the secondary) by the transformer's turns ratio, which is the ratio of the number of turns of wire in the primary winding to the number of turns in the secondary winding.

So, although the power in a transformer is conserved, the voltage and current levels are changed depending on the turns ratio of the transformer.

43. Wave nature and particle nature of photons related to its momentum

Actually, power is not exactly "unchanged" in a transformer. A transformer is an electrical device that is used to transfer electrical energy from one circuit to another through electromagnetic induction. In a transformer, the power that is transferred is equal to the input power, but the voltage and current levels can be changed. 

The power in a transformer is calculated using the equation P = VI, where V is the voltage and I is the current. In a transformer, the voltage and current on the input side (the primary) are related to the voltage and current on the output side (the secondary) by the transformer's turns ratio, which is the ratio of the number of turns of wire in the primary winding to the number of turns in the secondary winding.

So, although the power in a transformer is conserved, the voltage and current levels are changed depending on the turns ratio of the transformer.

44. In SONAR we use sound waves.

SONAR (Sound Navigation and Ranging) uses sound waves to detect objects underwater. The basic principle of SONAR is to emit a sound wave (usually a high-frequency pulse) from a transmitter and then measure the time it takes for the sound wave to bounce off an object and return to a receiver. By analyzing the time delay and frequency shift of the reflected sound wave, SONAR can determine the distance, size, and shape of underwater objects.

The sound waves used in SONAR are typically in the ultrasonic range with frequencies of 20 kHz or higher. This high frequency is necessary because sound waves at lower frequencies are absorbed more easily in water and do not travel as far. Additionally, the high frequency allows for better resolution of small objects and features underwater.

45. A perfect black body shows continuous spectrum.

A perfect black body is an idealized object that absorbs all radiation that falls upon it and emits radiation across the entire electromagnetic spectrum, including visible light, infrared radiation, ultraviolet radiation, and even X-rays and gamma rays. 

The radiation emitted by a black body is called blackbody radiation, or sometimes Planck radiation, after the physicist Max Planck who first described it.

The spectrum of radiation emitted by a black body is continuous, meaning that there are no gaps or interruptions in the range of wavelengths emitted. 

The exact shape of the spectrum depends on the temperature of the black body, with hotter objects emitting more high-energy radiation and cooler objects emitting more low-energy radiation.

46. Misconception: Wave nature of light is provided by polarization.

No, the wave nature of light is not provided by polarization. 

Light is an electromagnetic wave, which means that it consists of oscillating electric and magnetic fields that travel through space. The wave nature of light is a fundamental property of electromagnetic radiation and does not depend on its polarization.

Polarization refers to the orientation of the electric field vector of an electromagnetic wave. In a polarized wave, the electric field oscillates in a particular direction, whereas in an unpolarized wave, the electric field oscillates in all possible directions perpendicular to the direction of propagation. 

Polarization is an important property of light, and it can be used to filter, manipulate, and detect light in various applications, but it does not define the wave nature of light.

The wave nature of light can be demonstrated through various phenomena, such as interference, diffraction, and refraction, which cannot be explained by a particle model of light. These phenomena are characteristic of waves and show that light behaves like a wave with a certain frequency, wavelength, and velocity.

47. Misconception: Momentum principle used in solar cells.

The momentum principle, also known as the conservation of momentum, is not directly used in solar cells. 

Solar cells are devices that convert the energy of sunlight into electrical energy by the photoelectric effect, which involves the absorption of photons by a semiconductor material.

The conversion of sunlight into electrical energy in a solar cell is not related to the conservation of momentum, but rather to the conservation of energy and the transfer of energy from photons to electrons.

48. Work done by transition force in Simple pendulum is zero.

The work done by the transition force in a simple pendulum is zero over one complete cycle of motion. 

This is because the transition force, which is the component of the gravitational force that is perpendicular to the pendulum's displacement, is a conservative force. 

A conservative force is one for which the work done over a closed path is zero.

In a simple pendulum, the transition force acts to restore the pendulum bob to its equilibrium position as it swings back and forth. As the pendulum bob swings from its highest point to its lowest point, the transition force is in the direction opposite to the displacement of the bob. As the bob swings back from its lowest point to its highest point, the transition force is in the direction of the displacement of the bob.

Because the transition force is perpendicular to the displacement of the pendulum bob at its highest and lowest points, no work is done by the transition force on the pendulum bob at those points. 

As the pendulum bob swings from its highest point to its lowest point and back again, the transition force alternately acts in the opposite and the same direction as the displacement of the bob, so that the net work done over one complete cycle is zero.

Therefore, the work done by the transition force in a simple pendulum is zero over one complete cycle of motion, and the total energy of the pendulum, which is equal to the sum of its potential and kinetic energy, is conserved.

49. Misconception: Photon when scattered  from the mirror its momentum becomes double.

When a photon is scattered from a mirror, its momentum does not become double. 

In fact, the momentum of the photon is conserved during the scattering process, and it does not change unless an external force acts on it.

Scattering is a process in which a photon interacts with a target, such as a mirror, and changes direction. 

The scattering of a photon from a mirror is an example of elastic scattering, which means that the photon maintains its energy and momentum before and after the interaction.

When a photon is incident on a mirror, it is absorbed by the mirror and then re-emitted in a different direction. The direction of the scattered photon depends on the angle of incidence and the angle of reflection of the mirror, but its momentum is conserved. 

The momentum of the photon before scattering is equal to its momentum after scattering, as required by the law of conservation of momentum.

50. Radiation exchange occurs in vacuum.

The statement is teue. Radiation exchange can occur in vacuum. In fact, radiation is one of the three modes of heat transfer, the other two being conduction and convection. 

While conduction and convection require a medium for heat transfer, radiation can occur in vacuum as well as in a medium.

Radiation is the transfer of energy through electromagnetic waves, which can travel through vacuum. 

In vacuum, there are no particles to collide with or conduct heat, so radiation is the only mode of heat transfer. This is why objects in outer space, which is essentially a vacuum, lose heat through radiation.