Must know facts of Physics

Must know facts of Physics 

1. Electron Volt  is a unit of electric energy.

The electron volt (eV) is a unit of energy commonly used in atomic and nuclear physics, as well as in particle physics. 

It is defined as the amount of energy gained by a single electron when it moves through an electric potential difference of one volt.

In other words, if an electron is accelerated by an electric field with a potential difference of one volt, it will gain one electron volt of kinetic energy. 

The electron volt is a very small unit of energy, with one eV being equivalent to 1.602 x 10^-19 joules. 

It is often used to describe the energy of particles in accelerators and the energy levels of electrons in atoms.

2. "783 keV is the maximum kinetic energy that the electron can have in neutron beta decay."

In beta decay, a neutron in the nucleus of an atom decays into a proton, an electron, and an antineutrino. The electron carries away some of the energy released in the decay as kinetic energy.

The maximum kinetic energy that the electron can have is determined by the energy released in the decay and the mass difference between the neutron and the proton. This maximum kinetic energy is given by the Q value of the decay, which for neutron beta decay is approximately 0.78 MeV (780 keV).

3. Proton and neutron are composed of smaller particles called quark.

Protons and neutrons, which are the particles found in the nucleus of an atom, are made up of smaller particles called quarks. Quarks are elementary particles that are considered to be the building blocks of protons and neutrons, as well as other particles known as hadrons.

There are six types of quarks: up, down, charm, strange, top, and bottom. Protons are composed of two up quarks and one down quark, while neutrons are composed of two down quarks and one up quark.

Quarks are held together by the strong nuclear force, which is one of the four fundamental forces of nature, along with gravity, electromagnetism, and the weak nuclear force. The strong nuclear force is responsible for binding quarks together to form protons and neutrons, as well as for holding the nucleus of an atom together.

4. Misconception: Coherent source of light means single wave length.

Not necessarily. A coherent source of light means that the light waves are all in phase with each other, which can be achieved with a single wavelength of light or with multiple wavelengths.

In other words, coherence refers to the correlation between the phases of different waves, rather than the specific wavelength of the waves themselves. Coherent sources of light can have a single wavelength or a range of wavelengths, as long as the waves are in phase with each other.

For example, a laser is a coherent source of light that typically emits a single wavelength of light, but other types of coherent sources, such as certain types of LEDs or superluminescent diodes, can emit a range of wavelengths.

So, to summarize, a coherent source of light means that the waves are in phase with each other, and it is not necessarily related to the specific wavelength of the light.

5. Woolen clothes keep the body warm because of bad conductivity.

Woolen clothes are good at keeping the body warm because of their low thermal conductivity. Thermal conductivity is a measure of a material's ability to conduct heat, or in other words, to transfer heat from one point to another.

Wool is a good insulator because its fibers are naturally crimped and wavy, creating small pockets of air within the fabric. These pockets of air trap body heat and prevent it from escaping, keeping the body warm.

Additionally, wool fibers have a natural scale-like structure that helps to trap air even more effectively, making wool an even better insulator. 

This is why woolen clothes are often used for cold-weather clothing, as they provide excellent insulation and help to keep the body warm in cold temperatures.

So, to summarize, woolen clothes keep the body warm because of their low thermal conductivity, which allows them to trap body heat and prevent it from escaping.

6. Misconception: If centripetal force is zero then centrifugal force is also zero.

No, that's not correct. In fact, centripetal force and centrifugal force are two different and opposite forces that arise in a circular motion.

Centripetal force is the force that acts on an object moving in a circular path, directing it towards the center of the circle. It is always directed towards the center of the circle and is responsible for maintaining the object's circular motion.

On the other hand, centrifugal force is an apparent force that appears to act on an object moving in a circular path, pushing it away from the center of the circle. It is not a real force, but rather a result of the inertia of the object trying to maintain its original direction of motion.

If the centripetal force acting on an object is zero, it means that there is no force pulling the object towards the center of the circle. This would cause the object to move in a straight line, rather than in a circular path. However, the absence of centripetal force does not necessarily mean that the centrifugal force is zero.

In fact, according to Newton's Third Law, every action has an equal and opposite reaction. So, even if the centripetal force is zero, there would still be an apparent force acting on the object in the opposite direction of its motion, which is the centrifugal force.

Therefore, the statement "If centripetal force is zero then centrifugal also zero" is not correct.

7. Misconception: When the bulb is turned on ohm's law is not applicable.

Ohm's law is a fundamental law in physics that describes the relationship between the voltage across a conductor, the current flowing through it, and its resistance. 

According to Ohm's law, the current through a conductor is directly proportional to the voltage across it, and inversely proportional to its resistance, given by the equation I = V/R, where I is the current, V is the voltage, and R is the resistance of the conductor.

When a bulb is turned on, Ohm's law still applies, but only under certain conditions. When a bulb is off, it has a very high resistance, which means that only a small current will flow through it when a voltage is applied. However, when the bulb is turned on, its resistance decreases significantly, allowing a much larger current to flow through it.

Even though the resistance of the bulb changes, Ohm's law still applies to the bulb circuit as a whole, provided that the voltage and the resistance of the circuit are both constant. 

For example, if a bulb is connected in series with a resistor and a battery, Ohm's law can still be used to calculate the current flowing through the circuit, as long as the voltage across the circuit and the resistance of the circuit are known and constant. 

However, if the voltage or resistance of the circuit changes, Ohm's law may not be applicable and other laws, such as Kirchhoff's laws, may need to be used to analyze the circuit.

8. Negative of potential gradient is equal to electric intensity.

This statement is correct. The potential gradient, also known as the potential difference per unit length, is defined as the change in potential per unit length along a conductor or electric field. The electric field intensity, also known as the electric field strength, is defined as the force per unit charge experienced by a test charge placed in an electric field.

In a uniform electric field, the potential gradient is proportional to the electric field intensity, and the two are related by the equation:

E = - dV/dx

where E is the electric field intensity, dV/dx is the potential gradient, and the negative sign indicates that the electric field is in the direction of decreasing potential.

This relationship can also be written as:

dV = - E dx

which means that the potential difference between two points in an electric field is equal to the negative of the product of the electric field intensity and the distance between the two points. This relationship is often used to calculate the potential difference between two points in an electric field, given the electric field intensity and the distance between the two points.

9. If atomic mass increases, density does not change.

The density of a substance is defined as its mass per unit volume. 

Therefore, if the atomic mass of a substance increases while its volume remains constant, the density of the substance will increase. This is because the mass of the substance is directly proportional to its density, so an increase in atomic mass will result in a corresponding increase in density, assuming the volume remains constant.

However, if the atomic mass of a substance increases while its volume increases proportionally, the density of the substance will remain constant. This is because the increase in atomic mass is exactly balanced by the increase in volume, so the mass per unit volume remains the same.

It's worth noting that the relationship between atomic mass, volume, and density can be more complicated in some cases, especially for materials that undergo significant changes in their structure or composition when their atomic mass changes. 

In general, however, an increase in atomic mass will result in an increase in density if the volume of the substance remains constant.

10. Acceleration in Simple pendulum is always negative to displacement

The motion of a simple pendulum is characterized by the back-and-forth swing of a mass hanging from a fixed point by a string or rod. The motion of the pendulum can be described in terms of its displacement, velocity, and acceleration.

The acceleration of a simple pendulum is not always negative with respect to displacement. In fact, the direction of the acceleration changes with the direction of the displacement, and it is always directed towards the equilibrium position of the pendulum.

When the pendulum is at its maximum displacement, either to the left or the right of the equilibrium position, the acceleration is directed towards the equilibrium position and is therefore negative with respect to the displacement. As the pendulum moves towards the equilibrium position, the acceleration becomes smaller until it reaches zero at the equilibrium position.

As the pendulum continues to move past the equilibrium position, the acceleration begins to increase again, but this time in the opposite direction, towards the opposite maximum displacement. Therefore, the acceleration is negative with respect to the displacement when the pendulum is at its maximum displacement, but positive with respect to the displacement when the pendulum is passing through the equilibrium position.

In summary, the acceleration of a simple pendulum is not always negative with respect to displacement, but changes direction with the direction of the displacement, and is always directed towards the equilibrium position of the pendulum.