All questions of Physics for BPSC (Bihar) Exam

Understanding the Accelerated Expansion of the Universe
The accelerated expansion of the universe is primarily driven by a mysterious force known as dark energy.
What is Dark Energy?
- Dark energy is a form of energy that permeates all of space and tends to accelerate the expansion of the universe.
- It constitutes about 68% of the total energy density of the universe, making it a dominant component in cosmic dynamics.
Evidence for Dark Energy
- Observations from distant supernovae have shown that the universe is not just expanding, but the rate of expansion is increasing over time.
- The Cosmic Microwave Background radiation and large-scale structure observations further support the existence of dark energy.
Contrast with Other Forces
- Gravitational Pull of Matter: While gravity pulls matter together, it cannot explain the observed acceleration; instead, it would slow down the expansion.
- Electromagnetic Force: This force acts on charged particles and does not play a significant role in cosmic scales.
- Nuclear Force: Relevant at subatomic levels, it does not influence the large-scale structure of the universe.
Conclusion
The concept of dark energy reshapes our understanding of cosmology, suggesting that the universe's fate is tied to this enigmatic force. Its effects are profound, influencing the ultimate fate of the universe and challenging our understanding of physics.

Understanding Endoscopic Processes
Endoscopy is a medical procedure that allows doctors to view the inside of a patient's body using a flexible tube with a camera and light source. The principle that enables this visualization is based on total internal reflection of light.
What is Total Internal Reflection?
- Total internal reflection occurs when light travels from a denser medium to a less dense medium at an angle greater than the critical angle.
- In endoscopes, this principle is utilized to transmit light and images through optical fibers.
How It Works in Endoscopy
- Light Transmission: The endoscope contains numerous optical fibers that guide light. When light is sent through these fibers, it reflects internally, allowing it to bend around corners and maintain brightness.
- Image Capture: The camera at the end of the endoscope captures the light reflected from the tissue, creating a clear image for the physician to analyze.
Advantages of Using Total Internal Reflection
- Minimally Invasive: Endoscopy provides a less invasive alternative to traditional surgical methods, leading to quicker recovery times.
- High-Quality Images: The use of optical fibers ensures high-resolution images, which are crucial for accurate diagnosis.
Conclusion
In summary, the effectiveness of endoscopic procedures is largely due to the principle of total internal reflection, allowing for effective light transmission and high-quality imaging within the human body. This technology has revolutionized diagnostic and surgical techniques in medicine.

The Leaning Tower of Pisa does not fall because:

Explanation:
The Leaning Tower of Pisa is famous for its unintended tilt, which has been attracting tourists from all over the world. Despite its significant lean, the tower has managed to remain standing for centuries. The correct answer to why the tower does not fall is option 'D', which states that the vertical line through the center of gravity of the tower falls within the base. Let's explore this answer in more detail:

Center of Gravity:
The center of gravity is the point through which the entire weight of an object can be considered to act. In a symmetrical object, the center of gravity lies at the geometrical center. However, in an asymmetrical object like the Leaning Tower of Pisa, the center of gravity is shifted due to its tilt.

Effect of Tapering at the Top:
The tower is tapered at the top, which means it becomes narrower as it goes higher. This tapering helps in distributing the weight of the tower more evenly, reducing the stress on the lower parts. It prevents the tower from toppling over due to excessive weight at the higher levels.

Large Base Area:
The tower has a large base area, which provides stability and prevents it from tipping over. The weight of the tower is distributed over a larger surface area, reducing the pressure on the ground and maintaining its equilibrium.

Center of Gravity within the Base:
The most crucial factor that prevents the tower from falling is that the vertical line through the center of gravity of the tower falls within the base. This means that the imaginary line passing through the center of gravity always remains inside the footprint of the tower, ensuring its stability. If the center of gravity were to fall outside the base, the tower would lose its balance and topple over.

Conclusion:
The Leaning Tower of Pisa remains standing due to a combination of factors, including its tapered structure, large base area, and most importantly, the positioning of the center of gravity within the base. These factors work together to maintain the tower's equilibrium and prevent it from falling.

Assertion (A): A piece of ice added to the drink cools it.

Reason (R): Ice takes latent heat from the drink for melting resulting in the cooling of the drink.

The correct code for the given statements is option 'A'.

Explanation:

Understanding the Assertion:
When a piece of ice is added to a drink, it cools the drink. This can be observed in daily life when ice cubes are added to beverages like water, juice, or soda. The drink becomes colder after the ice cubes melt.

Understanding the Reason:
The reason behind this phenomenon lies in the concept of latent heat. Latent heat refers to the heat energy required to change the state of a substance without changing its temperature. In the case of ice, it has to absorb latent heat from its surroundings in order to melt.

When ice is added to a drink, it is at a lower temperature than the drink. As a result, heat energy from the drink flows into the ice, causing it to melt. This transfer of heat energy from the drink to the ice is called the latent heat of fusion. The heat energy is used to break the intermolecular bonds in the ice and convert it from a solid to a liquid state.

During this process, the drink loses heat energy to the ice, resulting in a decrease in the temperature of the drink. This is why the drink becomes colder when ice is added to it.

Explanation of the Code:
The correct code is option 'A' because both the assertion and reason are true, and the reason correctly explains the assertion.

Conclusion:
Adding a piece of ice to a drink cools it because ice absorbs heat energy from the drink for melting, resulting in a decrease in the temperature of the drink. This phenomenon is explained by the concept of latent heat.

• This statement is true. When an electric current passes through a metal wire, the electrical resistance of the wire causes some of the electrical energy to be converted into heat energy, leading to an increase in temperature.

• The collision of metal atoms with each other releases heat energy. This phenomenon is called the Joule effect or Joule heating. When an electric current passes through a metal wire, the free electrons in the wire collide with the metal atoms. This collision transfers kinetic energy to the metal atoms, which manifests as heat.

Flat Shape of the Universe:

The overall shape of the Universe according to scientific observations is considered to be flat. This conclusion is based on a variety of observations and measurements made by astronomers and cosmologists.

Cosmic Microwave Background Radiation:
One of the key pieces of evidence supporting the flat shape of the Universe comes from the Cosmic Microwave Background Radiation (CMB). The fluctuations in the CMB provide valuable information about the geometry of the Universe, and the data collected indicates that the Universe is flat.

Measurements of Large-Scale Structure:
Observations of the large-scale structure of the Universe, including the distribution of galaxies and galaxy clusters, also support the idea that the Universe is flat. These measurements suggest that the overall geometry of the Universe is consistent with a flat shape.

General Relativity:
The theory of General Relativity, proposed by Albert Einstein, also supports the idea of a flat Universe. According to General Relativity, the geometry of the Universe is determined by the distribution of matter and energy, and in a flat Universe, the total energy density is equal to the critical density.

Conclusion:
In conclusion, based on observations of the CMB, measurements of the large-scale structure of the Universe, and the predictions of General Relativity, scientists have determined that the overall shape of the Universe is flat. This has significant implications for our understanding of the cosmos and the fundamental nature of the Universe.

Understanding the Statements
The question presents three statements regarding sound and its propagation. Let's analyze each statement to determine their validity.
Statement 1: Two persons on the surface of the moon cannot talk to each other.
- This statement is correct.
- The moon has no atmosphere, meaning it is effectively a vacuum.
- Sound requires a medium (like air, water, or solids) to travel; without it, sound waves cannot propagate. Therefore, two astronauts would not be able to communicate verbally without the aid of radio equipment.
Statement 2: Sound waves cannot travel through vacuum.
- This statement is also correct.
- Sound is a mechanical wave that travels through the vibration of particles.
- In a vacuum, there are no particles to vibrate, which means sound cannot be transmitted. This is why there is silence in the vacuum of space.
Statement 3: Speed of sound is greater in solid medium than in liquid or gas medium.
- This statement is correct as well.
- The speed of sound varies in different media due to the density and elasticity of the material.
- In general, sound travels fastest in solids (due to closely packed particles facilitating quicker vibrations), followed by liquids, and slowest in gases.
Conclusion
Given that all three statements are correct, the correct answer is indeed option D: 1, 2, and 3 are correct. Each statement accurately reflects the principles of sound propagation and the properties of various media.

The Big Bang Theory:

The Big Bang Theory is a scientific explanation for the origin and evolution of the universe. It proposes that the universe began as an extremely hot and dense point, often referred to as a singularity, and has been expanding ever since. This theory is widely accepted by the scientific community and is supported by various lines of evidence.

Explanation:

1. Origin of the Universe:
The Big Bang Theory suggests that approximately 13.8 billion years ago, all matter and energy in the universe was concentrated in a tiny, infinitely dense point called a singularity. This singularity began to rapidly expand, resulting in the formation of the universe as we know it.

2. Expansion of the Universe:
According to the theory, the universe is constantly expanding. This expansion is evidenced by the observation of distant galaxies moving away from us. The expansion of the universe can be visualized by imagining dots on the surface of a balloon. As the balloon is inflated, the dots move away from each other, just like galaxies in our universe.

3. Background Radiation:
One of the key pieces of evidence supporting the Big Bang Theory is the discovery of cosmic microwave background radiation. This radiation is a faint glow of energy that permeates the entire universe and is thought to be the afterglow of the initial explosion. Its existence and characteristics align with the predictions made by the theory.

4. Abundance of Light Elements:
The Big Bang Theory also explains the abundance of light elements, such as hydrogen and helium, in the universe. It suggests that during the early moments of the universe, the extremely high temperatures and pressures allowed for the formation of these elements. Subsequent processes, such as nuclear fusion in stars, led to the creation of heavier elements.

5. Observable Universe:
The Big Bang Theory provides an explanation for the observed distribution and structure of galaxies in the universe. As the universe expanded, matter began to clump together under the influence of gravity, forming structures like galaxies, stars, and planets. The theory predicts the large-scale structure of the universe, including the existence of galaxy clusters and cosmic filaments.

Overall, the Big Bang Theory is a comprehensive scientific explanation for the origin and evolution of the universe. It provides a framework for understanding the vastness and complexity of the cosmos and is supported by numerous observational and theoretical evidence.

Understanding Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging (MRI) is a powerful diagnostic tool used in medical imaging. The principle behind MRI is based on a specific phenomenon known as nuclear magnetic resonance (NMR).
What is Nuclear Magnetic Resonance (NMR)?
- NMR is a technique that exploits the magnetic properties of atomic nuclei.
- When placed in a strong magnetic field, certain nuclei resonate at specific frequencies when exposed to radiofrequency (RF) radiation.
How MRI Utilizes NMR
- In the human body, hydrogen nuclei (protons) are abundant due to the high water content of tissues.
- MRI machines generate a strong magnetic field, aligning these hydrogen nuclei.
- An RF pulse is then applied, causing the protons to absorb energy and resonate.
Signal Detection and Imaging
- As the RF pulse is turned off, the protons relax back to their original alignment, releasing energy.
- This released energy is detected by the MRI machine and converted into signals.
- The signals are processed to create detailed images of internal structures, highlighting differences in tissue properties.
Significance of MRI
- MRI provides high-resolution images without the use of ionizing radiation, making it a safer alternative to X-rays and CT scans.
- It is particularly useful for imaging soft tissues, such as the brain, muscles, and ligaments.
In summary, the correct answer to why MRI is based on the phenomenon of nuclear magnetic resonance is due to its reliance on the magnetic properties of nuclei, primarily hydrogen in human tissues, to produce detailed diagnostic images.

**Explanation:**

The correct answer is option 'c' - The velocity of sound in air decreases as the humidity increases.

**Velocity of Sound in Air:**

The velocity of sound in air refers to the speed at which sound waves travel through the air. It depends on various factors such as temperature, pressure, and humidity.

**a) The velocity of sound in air increases with the increase of temperature:**

This statement is correct. The velocity of sound in air is directly proportional to the temperature of the air. As the temperature increases, the molecules of air gain more kinetic energy and vibrate more rapidly, which leads to an increase in the speed of sound. This relationship is known as the Gay-Lussac's law.

**b) The velocity of sound in air is independent of pressure:**

This statement is correct. The velocity of sound in air is not affected by changes in pressure. The pressure of the air only affects the density of the air, but not the speed at which sound waves travel through it. Therefore, the velocity of sound in air remains constant regardless of changes in pressure.

**c) The velocity of sound in air decreases as the humidity increases:**

This statement is incorrect. The velocity of sound in air is not significantly affected by changes in humidity. Humidity refers to the amount of water vapor present in the air. While water vapor molecules can absorb some sound energy, the effect of humidity on the velocity of sound is relatively small and negligible compared to the effects of temperature and pressure.

**d) The velocity of sound in air is not affected by the change in amplitude and frequency:**

This statement is correct. The velocity of sound in air is not affected by changes in the amplitude (loudness) or frequency (pitch) of the sound wave. These factors only affect the properties of the sound wave itself, but not the speed at which it travels through the air.

In conclusion, the statement that is NOT correct is option 'c' - The velocity of sound in air decreases as the humidity increases.

Answer:

When a rock is brought from the surface of the moon to the Earth, its weight will change but not its mass. The correct answer is option 'B'.

Explanation:

1. Distinction between Mass and Weight:
Before explaining the answer, it is important to understand the distinction between mass and weight.

- Mass: Mass is a fundamental property of matter and it is a measure of the amount of matter contained in an object. Mass remains constant regardless of the location or the gravitational field.
- Weight: Weight is the force with which an object is attracted towards the center of the Earth (or any other celestial body) due to gravity. Weight depends on the mass of the object and the gravitational field it is in.

2. Effect of Gravity on Weight:
The weight of an object depends on the gravitational field it is in. The gravitational field on the surface of the Moon is about 1/6th of the gravitational field on the surface of the Earth. This means that the Moon's gravitational pull on an object is approximately 1/6th of the Earth's gravitational pull.

3. Impact on Weight:
When a rock is brought from the surface of the Moon to the Earth, its weight will change but not its mass.

- On the surface of the Moon, the rock experiences a weaker gravitational pull compared to the Earth. As a result, its weight on the Moon is 1/6th of its weight on Earth.
- When the rock is brought to the Earth, it will experience a stronger gravitational pull. Therefore, its weight on Earth will be 6 times greater than its weight on the Moon.

4. No Change in Mass:
However, the mass of the rock remains the same throughout the process. The mass of an object is an inherent property and does not change with the location or the gravitational field it is in. So, bringing the rock from the Moon to the Earth does not change its mass.

Therefore, when a rock is brought from the surface of the Moon to the Earth, its weight will change but not its mass.