All questions of Physics for Computer Science Engineering (CSE) Exam

Mass of 1 a.m.u.
The atomic mass unit (a.m.u.), also known as the unified atomic mass unit, is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state.
- The mass equivalent of 1 a.m.u. is approximately 1.67 x 10^-27 kg.
Energy Equivalent of 1 a.m.u.
Using Einstein's mass-energy equivalence principle (E=mc²), we can convert mass into energy.
- The energy equivalent for 1 a.m.u. is calculated as follows:
- E = mc²
- c (speed of light) = 3 x 10^8 m/s
- Therefore, E = (1.67 x 10^-27 kg) * (3 x 10^8 m/s)²
- This results in approximately 930 MeV.
Conclusion
Thus, the values for 1 a.m.u. are:
- Mass: 1.67 x 10^-27 kg
- Energy: 930 MeV
This confirms that the correct answer is option B.

**Explanation:**

The correct answer is option **B) Distance**.

A light-year is a unit of distance used in astronomy to measure large distances in space. It is defined as the distance that light travels in one year in a vacuum. Since light travels at a constant speed of approximately 299,792 kilometers per second (or about 186,282 miles per second), the distance covered by light in one year is immense.

To better understand the concept of a light-year, let's break down the distance calculation and the significance of using this unit in astronomy:

**Definition of a Light-Year:**
- A light-year is the distance that light travels in one year.
- Light travels at a speed of about 299,792 kilometers per second (or about 186,282 miles per second).
- Therefore, in one year, light can travel about 9.46 trillion kilometers (or about 5.88 trillion miles).

**Importance of Light-Years in Astronomy:**
- The vast distances between celestial objects in space make it impractical to use conventional units like kilometers or miles.
- Astronomers use light-years to measure the distances between stars, galaxies, and other objects in the universe.
- Light-years allow us to comprehend the enormous scale of the universe and the time it takes for light to travel across such vast distances.

**Examples of Light-Years:**
- The nearest star to Earth, Proxima Centauri, is approximately 4.24 light-years away.
- The Andromeda Galaxy, our closest neighboring galaxy, is about 2.537 million light-years away.
- The observable universe is estimated to be about 93 billion light-years in diameter.

In conclusion, a light-year is a unit of distance used in astronomy to measure the vast distances between celestial objects. It represents the distance that light travels in one year and is an essential tool for understanding the scale and size of the universe.

Explanation:
A mirage is an optical illusion that occurs due to the bending of light rays. It is a phenomenon where distant objects appear to be shimmering, distorted, or displaced from their actual position. The correct answer is option 'D' because a mirage fits the description of an optical illusion.

Definition of a Mirage:
A mirage is a phenomenon that occurs when light rays bend due to the variation in air temperature. It usually happens in hot, desert-like environments where the ground is significantly heated. The bending of light causes an apparent displacement of objects, creating the illusion of water or reflections.

Causes of Mirage:
1. Temperature Gradient: Mirages occur due to the temperature gradient in the air. The air close to the ground is hotter than the air higher up. This temperature difference causes the light rays to bend as they pass through the layers of air with varying densities.

2. Total Internal Reflection: When light travels from one medium to another, it bends or refracts. In the case of a mirage, the temperature gradient causes the light rays to bend more than usual, leading to total internal reflection. This reflection creates the illusion of water or a shiny surface.

Types of Mirage:
1. Inferior Mirage: An inferior mirage is the most common type of mirage. It occurs when the air close to the ground is hotter than the air above. This causes the light rays to bend upwards, creating an image of objects below the actual position.

2. Superior Mirage: A superior mirage occurs when the air close to the ground is colder than the air above. In this case, the light rays bend downwards, creating an image of objects above their actual position. Superior mirages are often seen in cold Arctic regions.

Characteristics of a Mirage:
1. Shimmering Effect: Mirages create a shimmering effect, making the reflected image appear unstable or wavering.

2. Displacement: Mirages can displace the position of objects, making them appear higher or lower than their actual location.

3. Illusion of Water: One of the common characteristics of a mirage is the illusion of water. Due to the bending of light, distant objects may appear as if they are reflecting off a water surface.

4. Distance: Mirages often occur at a distance, particularly in desert areas where the ground is heated.

In conclusion, a mirage is an optical illusion that occurs due to the bending of light rays caused by a temperature gradient in the air. It creates the illusion of shimmering, displaced, or distorted objects, often resembling water or reflections.

Galvanizing: Protecting Iron from Rusting

Galvanizing is the method of protecting iron from rusting by coating it with a thin layer of zinc. It is a widely used technique to prevent corrosion and extend the lifespan of iron and steel objects. Let's delve into the details of galvanizing and why it is an effective method of protection.

1. What is Galvanizing?
Galvanizing is a process in which a layer of zinc is applied to the surface of iron or steel to create a protective barrier. The zinc coating acts as a sacrificial anode, meaning it corrodes instead of the iron or steel beneath it. This sacrificial action ensures that the iron or steel remains protected from rusting.

2. How is Galvanizing done?
The galvanizing process involves several steps:

2.1 Surface Preparation:
The surface of the iron or steel object is cleaned to remove any dirt, grease, or oxide layers. This step is crucial as it ensures proper adhesion of the zinc coating.

2.2 Immersion in a Zinc Bath:
The cleaned iron or steel object is immersed in a bath of molten zinc at a temperature of around 450°C. The object is carefully dipped into the bath, allowing the zinc to adhere to its surface.

2.3 Metallurgical Reaction:
During immersion, a metallurgical reaction occurs between the iron or steel and the molten zinc. This reaction forms a series of zinc-iron alloy layers on the surface of the object.

2.4 Cooling and Finishing:
After the object is removed from the zinc bath, it is allowed to cool, allowing the zinc coating to solidify and adhere firmly to the iron or steel surface. The galvanized object is then typically inspected for any defects or imperfections.

3. Advantages of Galvanizing:
Galvanizing offers several advantages as a method of protecting iron from rusting:

3.1 Corrosion Resistance:
The zinc coating provides excellent corrosion resistance to the iron or steel object, preventing rust formation even in harsh environments.

3.2 Longevity:
Galvanized objects have a longer lifespan compared to bare iron or steel. The zinc coating acts as a durable protective layer, extending the life of the object.

3.3 Cost-Effective:
Galvanizing is a cost-effective method of protection as it requires minimal maintenance. The initial investment in galvanizing pays off in terms of reduced repair and replacement costs.

3.4 Aesthetic Appeal:
Galvanized objects have a visually appealing silver-gray finish that is often desirable in architectural and decorative applications.

4. Applications of Galvanizing:
Galvanizing is widely used in various industries and applications, including:

- Construction: Galvanized steel is used in roofing, fencing, structural components, and other construction applications.
- Automotive: Galvanized parts are used in automobile manufacturing to enhance corrosion resistance.
- Agriculture: Galvanized equipment and structures are commonly used in farming and agricultural settings.
- Electrical: Galvanized electrical conduits and cable trays provide protection against corrosion.

In conclusion, galvanizing is a highly effective method of protecting iron from rusting by coating it with a thin layer of zinc. This process creates a barrier that prevents the iron

Understanding Laser Technology
Lasers are specialized devices that produce a specific type of light known as coherent light. Let's delve into why option 'B' is the correct answer.
What is Coherent Light?
- Coherent light consists of waves that are in phase with each other, meaning their peaks and troughs align perfectly.
- This results in a concentrated beam of light that can travel long distances without spreading out significantly.
Characteristics of Laser Light
- Monochromatic: Laser light is typically of a single wavelength, which means it appears as one color. This characteristic is essential in applications like laser surgery and optical communication.
- Highly Directional: Unlike ordinary light sources, lasers emit light in a narrow beam. This directionality allows for precise targeting, making lasers useful in various fields, including medicine and industry.
- High Intensity: The coherent nature of laser light means that it can achieve much higher intensities compared to regular light sources, allowing for powerful applications like cutting and engraving.
Why Not Other Options?
- A) Beam of White Light: White light is composed of multiple wavelengths and is not coherent.
- C) Microwaves: While microwaves are a form of electromagnetic radiation, they do not fall under the category of laser light.
- D) X-rays: X-ray production involves different mechanisms and does not produce coherent light as lasers do.
Conclusion
In summary, lasers are designed to produce coherent light, characterized by its monochromatic, directional, and intense properties, making option 'B' the correct answer. Understanding these features is crucial for grasping how lasers are utilized in various scientific and practical applications.

Explanation:

Density Measurement:
- Pycnometer is an instrument used to measure the density of liquids or solids.
- It is a small glass bottle with a stopper that has a capillary tube attached to it.
- The pycnometer is weighed empty and then filled with the substance whose density is to be measured.
- The weight of the filled pycnometer is then recorded.
- By knowing the weight of the substance and the volume of the pycnometer, the density can be calculated using the formula: Density = Mass/Volume.

Other Options:
- Intensity of solar radiation is measured using instruments like pyranometer or radiometer.
- Intensity of earthquakes is measured using seismometers and seismographs.
- High temperatures are measured using thermometers or pyrometers.
Therefore, the correct answer is option 'A', as pycnometer is specifically designed for measuring density.

Why Tape Recorders Should Not Be Near Magnets
Tape recorders operate by using magnetic tape to record audio. The integrity and quality of the recorded sound are highly dependent on the magnetic properties of the tape. Here's why keeping tape recorders away from magnets is crucial:
1. Magnetic Interference
- Magnets produce a magnetic field that can disrupt the magnetic particles on the tape.
- This interference can lead to distortion or loss of the recorded audio.
2. Data Loss
- Exposure to strong magnetic fields can erase or alter the information stored on the tape.
- Even weak magnets can cause degradation over time, potentially leading to irreversible damage.
3. Recording Quality
- The presence of a magnet can negatively affect the tape's ability to capture sound accurately.
- It may result in poor sound quality, making the recordings unusable.
Additional Considerations
- Other devices like clocks, electrical switchboards, and radios do not typically generate strong magnetic fields that could affect tape recorders.
- Keeping tape recorders away from magnetic sources ensures the longevity and reliability of your recordings.
In conclusion, to maintain the functionality and quality of your tape recordings, it is essential to keep tape recorders away from magnets. This simple precaution can save you from potential data loss and ensure your recordings remain clear and intact.

Explanation:
When two vectors are added, they can either give zero or a resultant vector. However, when three or more vectors are added, they can never give zero as the resultant vector. Let's understand why:

Two vectors:
When two vectors are added, they can either give zero or a resultant vector. If the two vectors are of the same magnitude and opposite in direction, they will give a resultant vector of zero. For example, if two forces of 5 N each are applied in opposite directions, they will cancel out each other and the net force will be zero.

Three vectors:
When three vectors are added, they can never give zero as the resultant vector. The reason is that three vectors can form a triangle, and the sum of any two sides of a triangle is always greater than the third side. Therefore, there will always be a resultant vector when three vectors are added.

Four or more vectors:
When four or more vectors are added, they can never give zero as the resultant vector. The reason is that four or more vectors can form a polygon, and the sum of any two sides of a polygon is always greater than the third side. Therefore, there will always be a resultant vector when four or more vectors are added.

Therefore, the minimum number of unequal vectors which can give zero resultant are two.

The attenuation of light as it passes through a medium.

Understanding the Ozone Layer
The ozone layer, located in the Earth's stratosphere, plays a crucial role in protecting life on our planet by absorbing the majority of the Sun's harmful ultraviolet (UV) radiation.
Impact of Ozone Layer Absence
Without the ozone layer, the following types of rays would have a significant impact on the Earth's atmosphere:

• Infrared Rays: These rays are primarily responsible for heat. They can penetrate the atmosphere without significant absorption by ozone.
• Visible Light: This light is vital for life, as it enables photosynthesis in plants. Visible light can easily pass through the atmosphere and is unaffected by the ozone layer.
• Ultraviolet Rays: This is the key focus. UV rays are divided into three types: UVA, UVB, and UVC. The ozone layer absorbs the majority of UVB and all UVC rays, which are the most harmful. In the absence of the ozone layer, these rays would penetrate the atmosphere, leading to severe consequences for living organisms, including increased skin cancers and cataracts in humans, as well as detrimental effects on ecosystems.
• X-rays: These rays are highly energetic and are mostly blocked by both the ozone layer and the Earth's atmosphere. They would not significantly enter the atmosphere in the absence of the ozone layer.

Conclusion
In summary, the absence of the ozone layer would primarily allow harmful ultraviolet rays to enter the atmosphere, posing serious risks to health and the environment. Hence, option 'C' is correct.

Understanding Audible Sounds
Sounds are classified based on their frequencies, which are measured in Hertz (Hz). The human ear can perceive a specific range of frequencies, which is crucial for communication and interaction with the environment.
Frequency Range of Audible Sounds
- Audible Sounds: The range of sound frequencies that humans can hear is approximately 20 Hz to 20,000 Hz (20 kHz).
- This range is commonly referred to as audible sound.
Other Sound Classifications
- Ultrasonics: Frequencies above 20 kHz (20,000 Hz) are known as ultrasonics. These sounds are inaudible to humans but can be detected by certain animals and used in various technologies (e.g., ultrasound imaging).
- Infrasonics: Frequencies below 20 Hz are classified as infrasonics. These sounds are also inaudible to humans and can occur naturally (e.g., earthquakes) or be generated artificially.
- Megasonics: This term is less commonly used and generally refers to very high-frequency sounds, typically above ultrasonics, often used in specialized applications.
Conclusion
In summary, sounds within the frequency range of 20 Hz to 20,000 Hz are termed audible sounds, making option 'A' the correct answer. This classification helps in understanding how humans interact with sound and its applications in technology, medicine, and environmental studies.

Electrons