Physics

41. Automobiles are fitted with a device that shows the distance travelled

Automobiles are fitted with a device that shows the distance travelled. Such a device is known as

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Speedometer
Cathetometer
Odometer
Lactometer
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Different devices are used in automobiles to measure various parameters:
– Speedometer: Measures the instantaneous speed of the vehicle.
– Odometer: Measures the total distance traveled by the vehicle.
– Tachometer: Measures the engine’s rotational speed (RPM).
– Fuel gauge: Indicates the amount of fuel in the tank.

A Cathetometer is a laboratory instrument used to measure vertical distances precisely. A Lactometer is an instrument used to check the purity of milk by measuring its density.

Therefore, the device fitted in automobiles that shows the distance traveled is an odometer.

– An odometer is specifically designed to measure the distance covered by a vehicle.
– A speedometer measures speed.
– Other options are not used in automobiles for measuring distance traveled.
Modern odometers are typically digital, while older vehicles used mechanical odometers with rotating number wheels. The term “odometer” comes from the Greek words ‘hodos’ (way or path) and ‘metron’ (measure). Trip meters are usually integrated with the odometer and can be reset to measure distances for specific journeys.

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42. The phenomenon of change of a liquid into vapours at any temperature i

The phenomenon of change of a liquid into vapours at any temperature is known as evaporation, which takes place

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at its boiling point
above its boiling point
below its boiling point
at room temperature
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Evaporation is the process by which a liquid changes into a gas or vapor. This process occurs at the surface of the liquid. Unlike boiling, which happens at a specific temperature (the boiling point) throughout the bulk of the liquid when its vapor pressure equals the surrounding pressure, evaporation can happen at *any* temperature where the liquid exists. Molecules at the surface gain enough kinetic energy to overcome the intermolecular forces holding them in the liquid phase and escape into the gas phase. This process occurs *below* the boiling point of the liquid.
– Evaporation is a surface phenomenon.
– It occurs when liquid molecules gain enough energy to escape into the gas phase.
– Evaporation can take place at any temperature where the liquid is present.
– Boiling is different; it occurs throughout the liquid at a specific temperature (boiling point) where vapor pressure equals external pressure.
Factors affecting the rate of evaporation include temperature (higher temperature, faster evaporation), surface area (larger area, faster evaporation), humidity (lower humidity, faster evaporation), and wind speed (higher wind speed, faster evaporation). Evaporation is a cooling process because the molecules with the highest kinetic energy escape from the liquid surface.

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43. Bose-Einstein Condensate (BEC) is formed by cooling a gas of extremely

Bose-Einstein Condensate (BEC) is formed by cooling a gas of extremely low density, about one-hundredthousandth the density of normal air. This is treated as

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II state of matter
III state of matter
IV state of matter
V state of matter
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The common states of matter are Solid, Liquid, and Gas. Plasma is often considered the fourth state of matter, existing at very high temperatures where electrons are stripped from atoms. Bose-Einstein Condensate (BEC) is a distinct state of matter that occurs when a gas of bosons is cooled to temperatures very close to absolute zero. In a BEC, a large fraction of the bosons occupy the lowest quantum mechanical state, and macroscopic quantum phenomena become apparent. It is typically referred to as the fifth state of matter, following Solid, Liquid, Gas, and Plasma.
– The traditional states of matter are solid, liquid, and gas.
– Plasma is often considered the fourth state.
– Bose-Einstein Condensate (BEC) is a distinct state formed at extremely low temperatures and is considered the fifth state.
Bose-Einstein condensates were first experimentally realized in 1995 by Eric Cornell and Carl Wieman at the University of Colorado at Boulder, using a gas of rubidium atoms. They received the Nobel Prize in Physics in 2001 for this achievement, shared with Wolfgang Ketterle of MIT, who produced BECs in other atoms and demonstrated their properties. Fermionic condensates, a similar state for fermions, are sometimes referred to as the sixth state of matter.

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44. Newton’s law of motion cannot be applicable to the particles moving at

Newton’s law of motion cannot be applicable to the particles moving at a speed comparable to the speed of

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light
sound
rocket
bullet train
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Newton’s laws of motion are fundamental principles of classical mechanics. Classical mechanics provides an accurate description of the motion of objects in everyday life. However, these laws break down and are not applicable under certain extreme conditions:
1. When the speed of the object is comparable to the speed of light (approximately 3 x 10^8 m/s). In this regime, motion must be described by Einstein’s theory of special relativity. Relativistic effects like time dilation and length contraction become significant.
2. When the size of the object is very small (atomic or subatomic scales). In this regime, quantum mechanics is required to describe the behavior of particles.

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The speed of sound, rockets, and bullet trains are all vastly lower than the speed of light, so classical mechanics (and Newton’s laws) apply accurately to objects moving at these speeds.

– Newton’s laws are part of classical mechanics.
– Classical mechanics is an approximation that works well for macroscopic objects at relatively low speeds.
– It fails when speeds approach the speed of light (requiring relativity) or at very small scales (requiring quantum mechanics).
The speed of light is a fundamental constant in the universe. No object with mass can reach or exceed the speed of light. Particles moving at speeds close to light speed are typically subatomic particles accelerated in particle accelerators.

45. Consider the following statements : Statement-I : Giant stars live muc

Consider the following statements :
Statement-I :
Giant stars live much longer than dwarf stars.
Statement-II :
Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.
Which one of the following is correct in respect of the above statements ?

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Both Statement-I and Statement-II are correct and Statement-II explains Statement-I .
Both Statement-I and Statement-II are correct, but Statement-II does not explain Statement-I
Statement-I is correct, but Statement-II is incorrect
Statement-I is incorrect, but Statement-II is correct
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The question asks about the lifespan and nuclear reactions in giant stars compared to dwarf stars.
Statement-I: “Giant stars live much longer than dwarf stars.” This statement is incorrect. Giant stars, being more massive than dwarf stars (like our Sun, a G-type dwarf), have much stronger gravitational forces. This results in higher temperatures and pressures in their cores, which accelerates the rate of nuclear fusion. Although they have more fuel, they burn it at a vastly higher rate, leading to significantly shorter lifespans compared to dwarf stars. Dwarf stars, with their slower rate of fusion, can live for billions or even trillions of years.
Statement-II: “Compared to dwarf stars, giant stars have a greater rate of nuclear reactions.” This statement is correct. As explained above, the higher core temperatures and pressures in giant stars lead to a much higher rate of nuclear fusion reactions (converting hydrogen to helium) compared to dwarf stars. This high reaction rate is responsible for their high luminosity.
Statement I is incorrect, and Statement II is correct. Statement II actually explains *why* Statement I is incorrect (higher reaction rate leads to shorter lifespan). Therefore, Option D is the correct choice.
A star’s lifespan is primarily determined by its mass and luminosity (rate of energy output, which is proportional to the rate of nuclear reactions). More massive stars have more fuel but burn it much faster due to higher core temperatures and pressures, resulting in shorter lives. Less massive stars burn their fuel slowly and live much longer. Giant stars are typically more massive and much more luminous than dwarf stars.
Stars evolve through different stages, including dwarf phases, giant phases (like red giants or supergiants), and eventually remnant stages (like white dwarfs, neutron stars, or black holes), depending on their initial mass. The term “dwarf star” usually refers to main-sequence stars (like the Sun), while “giant star” refers to later evolutionary stages after the star has exhausted the hydrogen in its core and expanded significantly.

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46. Consider the following actions: 1. Detection of car crash/collision

Consider the following actions:

  • 1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously.
  • 2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
  • 3. Detection of the tilt of smartphone which results in the rotation of display between portrait and landscape mode

In which of the above actions is the function of a gyroscope is used?

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1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3
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The correct option is D, indicating that the function of a gyroscope is used in all three actions.
A gyroscope measures angular velocity (rate of rotation). In modern devices, gyroscopes are often used alongside accelerometers (which measure linear acceleration and tilt due to gravity) in Inertial Measurement Units (IMUs) to determine full 3D orientation and motion.
1. **Car crash/collision:** Advanced automotive crash detection systems use IMUs containing both accelerometers and gyroscopes. While accelerometers are crucial for detecting sudden deceleration (impact), gyroscopes can provide data on the vehicle’s rotation (pitch, roll, yaw) during a crash sequence, which is vital for determining the severity and type of crash (e.g., rollover) and optimizing airbag deployment strategies. Thus, the function of a gyroscope is used.
2. **Laptop accidental free fall:** Many modern laptops have sensors to detect free fall and suddenly stop the hard drive head to prevent damage upon impact. While accelerometers are primary in detecting the acceleration due to gravity and the subsequent impact deceleration, gyroscopes can be used in conjunction to better characterize the motion (e.g., determining if the laptop is rotating during the fall), improving the accuracy and reliability of the free fall detection system. Thus, the function of a gyroscope can be used.
3. **Smartphone tilt for display rotation:** While the basic detection of static tilt relative to gravity is done by accelerometers, modern smartphones use gyroscopes in combination with accelerometers (IMU) for more accurate, stable, and responsive orientation sensing. The gyroscope measures angular velocity, allowing the phone to detect rotations quickly and smoothly, distinguish intentional rotations from accidental movements, and provide faster screen transitions between portrait and landscape modes. Thus, the function of a gyroscope is used.
IMUs provide six degrees of freedom (6-DOF) motion sensing (three axes of acceleration, three axes of angular velocity). This combined data allows for robust tracking of movement and orientation in 3D space, enabling these and many other features in various devices.

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47. Consider the following statements : 1. Carbon fibres are used in the

Consider the following statements :

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  • 1. Carbon fibres are used in the manufacture of components used in automobiles and aircraftes.
  • 2. Carbon fibres once used cannot be recycled.

Which of the statements give above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2
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The correct option is A, meaning only statement 1 is correct.
Statement 1 is correct. Carbon fibres and carbon fibre composites (CFRPs) are widely used in high-performance applications due to their high strength-to-weight ratio, stiffness, and corrosion resistance. They are integral in the manufacture of structural components for aircraft (e.g., wings, fuselage parts) and high-end automobiles (chassis, body panels), as well as sports equipment and wind turbine blades.
Statement 2 is incorrect. While challenging and less developed than traditional material recycling, carbon fibre composites *can* be recycled using various methods, including mechanical recycling (shredding/milling), pyrolysis (thermal decomposition), and solvolysis (chemical decomposition). Recycled carbon fibres can then be used in new composite materials. The infrastructure and economic viability are still developing, but it is not true that they *cannot* be recycled.
The recycling of carbon fibre composites is an active area of research and development aimed at reducing waste from manufacturing and end-of-life products and recovering valuable materials.

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48. Which one of the following is a reason why astronomical distances are

Which one of the following is a reason why astronomical distances are measured in light-years?

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Distances among stellar bodies do not change.
Gravity of stellar bodies does not change.
Light always travels in straight line.
Speed of light is always same.
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The correct answer is D) Speed of light is always same.
Astronomical distances are vast, making standard units like kilometres or miles impractical. A light-year is defined as the distance light travels in one year in a vacuum. The use of light-years as a unit of distance in astronomy is based on the fact that the speed of light in a vacuum is a constant (approximately 299,792,458 meters per second). This constant speed provides a reliable basis for measuring extremely large distances across space based on time.
Options A, B, and C are incorrect. Distances between celestial bodies do change (due to cosmic expansion, orbital motion, etc.). Gravity of stellar bodies also changes depending on mass distribution and distance. While light travels in approximately straight lines in uniform media, it can be bent by gravity (gravitational lensing). The constancy of the speed of light is the fundamental principle behind using light-years to measure distance.

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49. With reference to street-lighting, how do sodium lamps differ from LED

With reference to street-lighting, how do sodium lamps differ from LED lamps?

  • 1. Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps.
  • 2. As street-lights, sodium lamps have longer life span than LED lamps.
  • 3. The spectrum of visible light from sodium lamps is almost monochromatic while LED lamps offer significant colour advantages in street-lighting.

Select the correct answer using the code given below.

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3 only
2 only
1 and 3 only
1, 2 and 3
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Statement 1 is correct. Traditional sodium lamps (like high-pressure sodium lamps) emit light omnidirectionally (in all directions), requiring reflectors to direct light downwards onto the street. LED lamps, by contrast, are inherently directional light sources, meaning they emit light primarily in a specific direction (forward). This directional nature allows for more efficient targeting of light where needed. Statement 2 is incorrect. LED lamps generally have a much longer lifespan (typically 50,000 to 100,000+ hours) compared to sodium lamps (typically 20,000 to 30,000 hours). Statement 3 is correct. High-pressure sodium lamps produce a predominantly yellow-orange light, resulting in poor color rendering (objects appear unnatural or monochrome). LED lamps can produce white light with various color temperatures and offer significantly better color rendering index (CRI), which improves visibility, recognition of objects and colors, and safety under street lighting.
– Sodium lamps emit light omnidirectionally, while LEDs are directional.
– LEDs have a significantly longer lifespan than sodium lamps.
– Sodium lamps provide poor color rendering (monochromatic light), while LEDs offer much better color rendering.
LED street lights also offer advantages in terms of energy efficiency (lower power consumption), instant on/off capability, dimmability, and environmental benefits (no mercury). These factors have led to a widespread shift from sodium vapor lamps to LED technology for street lighting globally.

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50. In a pressure cooker, the temperature at which the food is cooked depe

In a pressure cooker, the temperature at which the food is cooked depends mainly upon which of the following?

  1. Area of the hole in the lid
  2. Temperature of the flame
  3. Weight of the lid

Select the correct answer using the code given below.

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1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3
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The temperature at which food is cooked in a pressure cooker depends mainly upon the area of the hole in the lid and the weight of the lid.
– A pressure cooker works by creating a sealed environment that traps steam, increasing the internal pressure.
– The boiling point of water increases with pressure. At standard atmospheric pressure (1 atm), water boils at 100°C (212°F). In a pressure cooker, the pressure can rise to about 2 atm (or more), raising the boiling point to around 120-125°C (248-257°F).
– The maximum pressure inside the cooker is regulated by a pressure release valve, which typically consists of a small hole or vent in the lid covered by a weight or spring mechanism.
– The pressure at which steam is released depends directly on the weight placed on the vent and inversely on the area of the vent hole under the weight. A heavier weight or a smaller hole area will result in higher pressure and thus a higher cooking temperature.
– The temperature of the flame affects the *rate* at which the water heats up and turns into steam, and thus how quickly the desired pressure is reached. However, once the pressure regulator starts venting steam, the temperature inside stabilizes at a level determined by the pressure, not the flame temperature (as long as the heat input is sufficient to maintain that pressure).
– Therefore, the main factors determining the cooking temperature are the weight of the lid (specifically the pressure regulator) and the area of the hole it covers, which together regulate the internal pressure.
Cooking at a higher temperature under pressure significantly reduces cooking time compared to boiling at atmospheric pressure. Different pressure cookers and their regulators are designed to operate at specific pressures, typically “low” or “high” pressure settings, corresponding to different weights or spring tensions.

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