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Physics — UPSC Prelims Science & Environment previous year questions

177 solved previous year questions on Physics, papers from 1990 to 2023, drawn from UPSC CSE Prelims, UPPCS, UPSC CDS. Each carries the printed answer key and the explanation from the source compilation.

1. #1UPSC CSE Prelims 2021
   Which one of the following is why astronomical distances are measured in light-years?
   • ADistances among stellar bodies do not change
   • BGravity of stellar bodies does not change
   • CLight always travels in straight line
   • DSpeed of light is always same
   Answer: (D) Speed of light is always same
   Explanation

   Option d is the correct light-year is a measurement of distance in space. distances are measured in light-years speed of light is constant throughout the universe known to high precision. In a vacuum, light travels mph (1,079,252,849 km/h). To find the a light-year, you multiply this speed by the number in a year (8,766). The result: One light-year miles (9.5 trillion km). At first glance, seem like an extreme distance, but the enormous the universe dwarfs this ir, light-years also allows astronomers how far back in time they are viewing. takes time to travel to our eyes, everything we view night sky already happened. In other words, observe something 1 light-year away, you see it as exactly one year ago

2. #2UPSC CSE Prelims 2013
   Many transplanted seedlings do not grow because
   • Athe new soil does not contain favorable minerals
   • Bmost of the root hair grip the new soil too hard
   • Cmost of the root hairs are lost during transplantation
   • Dleaves get damaged during transplantation
   Answer: (C) most of the root hairs are lost during transplantation
   Explanation

   Option c is the correct l is correct: Visible Light Communication light, which is a part of the electromagnetic wavelengths ranging from 375 to 780 2 is incorrect: VLC is not known as wireless communication, but rather as a short range communication technology that works best in Long-range optical wireless refers to free-space optical communication uses infrared or near-infrared light to transmit long distances in outdoor 3 is correct: VLC can transmit large data faster than Bluetooth, which is another that uses radio waves. VLC can achieve data up to 500 Mbit/s with LEDs and even higher with Bluetooth can only reach up to 50 4 is correct: VLC has no because it does not use radio waves, which to interference from other devices or sources. does not interfere with other wireless technologies radio waves, such as Wi-Fi or cellular networks

3. #3UPSC CSE Prelims 2013
   The known forces of nature can be divided into four classes, viz., gravity, electromagnetism, weak nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?
   • AGravity is the strongest of the four
   • BElectromagnetism acts only on particles with an electric charge
   • CWeak nuclear force causes radioactivity
   • DStrong nuclear force holds protons and neutrons inside the nucleus of an atom
   Answer: (A) Gravity is the strongest of the four
   Explanation

   Option a is the correct are four fundamental forces in nature which force, Strong nuclear force, Weak nuclear Electromagnetic force. These forces prevent the matter in the universe and helps keep it together. Gravitational force (Gravity) is the weakest force but has an infinite range. Strong nuclear force: This force holds the nucleus of an atom together. It is the strongest of the forces, but it is very short Weak nuclear Force: This force is weak compared to the strong nuclear force as the name implies and has the shortest Electromagnetic Force: This is the second strongest force after the strong nuclear force and it acts on electrically charged particles

4. #4UPSC CSE Prelims 2013
   Rainbow is produced when sunlight falls on drops of rain. Which of the following physical phenomena are responsible for this? 1. Dispersion 2. Refraction 3. Internal reflectionSelect the correct answer using the codes below
   • A1 and 2 only
   • B2 and 3 only
   • C1 and 3 only
   • D1, 2 and 3
   Answer: (D) 1, 2 and 3
   Explanation

   Option d is the correct answer. Reflection Internal Reflection Primary rainbow sunlight falls on the drops of rain formation of occurs in the sky. These droplets work as a the rays coming from the sun. When the sunlight these droplets, it results in refraction and seven colours known as. Then it goes internal reflection. This happens due to of Dispersion, Refraction, and Total in the atmosphere. Important Tips Dispersion is the process of splitting lights into different colours. Example: Dispersion done by Prism. Each individual droplet of water acts as a tiny prism that both disperses the light and reflects it back to our eye nlm Total Internal reflection is the phenomenon that occurs based on 2 When light moves from a denser medium to a less dense medium. When the angle of incidence is greater than the critical angle

5. #5UPSC CSE Prelims 2013
   Consider the following phenomena: 1. Size of the sun at dusk. 2. Color of the sun at dawn 3. Moon being visible at dawn 4. Twinkle of stars in the sky 5. Polestar being visible in the skyWhich of the above are optical illusions?
   • A1, 2 and 3
   • B3, 4 and 5
   • C1, 2 and 4
   • D2, 3 and 5
   Answer: (C) 1, 2 and 4
   Explanation

   Option c is the correct of the stars are shining with a steady light. The air (sometimes called turbulence) in the atmosphere causes the starlight to get slightly bent as it the distant star through the atmosphere down to us ground. The twinkling of a star is due to of starlight. The starlight, on entering the undergoes refraction continuously before the earth. The atmospheric refraction occurs in of gradually changing refractive means that some of the light reaches us directly gets bent slightly away. To our eyes, this makes the to twinkle. Important Tips An optical illusion is a visual stimuli that is perceived by the eyes and then comprehended by the brain in a way that is different from reality

6. #6Previous year
   The efforts to detect the existence of Higgs boson particle have become frequent news in the recent past. What is/are the importance of discovering this particle? 1. It will help us to understand as to why elementary particles have mass. 2. It will enable us in the near future to develop the technology to transfer matter from one point to another without traversing the physical space between them. 3. It will enable us to create better fuel for nuclear fission.Select the correct answer using the codes given below: [UPSC CSE Pre 2013)
   • A1 only
   • B2 and 3 only
   • C1 and 3
   • D1, 2 and 3
   Answer: (A) 1 only
   Explanation

   Option a is the correct l is correct: The Higgs boson is it confirms the existence of the Higgs field, responsible for giving mass to elementary particles. of the Higgs boson validates the standard model physics, which describes the fundamental forces of 2 is incorrect: The statement 2 is a of teleportation, which has no connection to field or 3 is incorrect: The statement 3 is about which involves splitting heavy nuclei into releasing energy. The Higgs boson does not affect or the fuel used for it. Important Tips The Higgs boson is a very important particle in the standard model of particle physics. It is the result of the quantum excitation of the Higgs field, which is a field that fills the entire universe and gives mass to other elementary particles. The Higgs boson was predicted by several physicists in 1964, but it was only discovered in 2012 by the ATLAS and CMS experiments at the

7. #7Previous year
   When the bark of a tree is removed in a circular fashion all around near its base, it gradually dries up or dies because- [UPSC CSE Pre
   • AWater from soil cannot rise to aerial parts
   • BRoots are starved of energy
   • CTree is infected by the soil microbes
   • DRoots do not receive oxygen for respiration
   Answer: (B) Roots are starved of energy
   Explanation

   Option bis the correct the bark of a tree is removed in a circular fashion near its base, the phloem tissue is damaged. is responsible for transporting food from the leaves roots. Without phloem tissue, the roots cannot food they need to survive. Important Tips Phloem and Xylem: Phloem is responsible for transporting food from the leaves to the rest of the plant. The food that is transported in phloem is made up of sugars, amino acids, and other organic molecules. Xylem is responsible for transporting water and minerals from the roots to the rest of the plant. The water and minerals that are transported in xylem are dissolved in water

8. #8UPSC CSE Prelims 2011
   What is the difference between a CFL and an LED Lamp? 1. To produce light, a CFL uses mercury vapour and phosphor while an LED lamp uses semi-conductor material. 2. The average life span of a CFL is much longer than of an LED lamp. 3. A CFL is less energy efficient as compared to an LED lamp.Which of the statements given above is/are correct?
   • A1 only
   • B2 and 3 only
   • C1 and 3 only
   • D1, 2 and 3
   Answer: (C) 1 and 3 only
   Explanation

   Option c is the correct l is correct- CFLs (compact fluorescent mercury vapor to create ultraviolet light, which is to visible light by a phosphor coating. On hand, LED employs semiconductor material Indium gallium nitride which is utilized for creating high-brightness LEDs in blue, green, and ultraviolet Aluminium gallium indium phosphide which is used to manufacture high-brightness LEDs in yellow, orange, and red hues. Aluminium gallium arsenide employed for crafting red and infrared 2 is incorrect- LED lamps have a much than CFLs. CFLs typically have a lifespan of 15,000 hours, while LED lamps typically have a 25,000 to 50,000 3 is correct- LED lamps are more energy efficient than CFLs. This is because LEDs produce with less energy

9. #9Previous year
   Which one among the following has the highest energy? [UPSC CSE Pre 2009)
   • ABlue light
   • BGreen light
   • CRed light
   • DYellow light
   Answer: (A) Blue light
   Explanation

   Option a is the correct with a shorter wavelength has higher energy This is because the energy of a photon is given equation E he/A, where h is Planck's constant, c is of light, and A is the wavelength of the photon. of a photon is directly proportional to its inversely proportional to its wavelength. Blue light shorter wavelength and higher frequency compared other colors listed, making it the one with the among them

10. #10Previous year
    In the context of alternative sources of energy, ethanol as a viable biofuel can be obtained from: [UPSC CSE Pre 2009)
    • APotato
    • BRice
    • CSugarcane
    • DWheat
    Answer: (C) Sugarcane
    Explanation

    Option c is the correct is a renewable fuel that can be made from a feedstocks, including sugarcane. To produce ethanol the sugarcane juice is first extracted from The juice is then fermented with yeast to The ethanol is then distilled and purified to fuel-grade product. Sugarcane is a good source of it has a high sugar content. Sugarcane ethanol is fuel that can help to reduce greenhouse

11. #11UPSC CSE Prelims 2008
    A person is sitting in a car which is at rest. The reaction from the road at each of the four wheels of the car is R. When the car runs on a straight level road, how will the reaction at either of the front wheels vary?
    • AIt will be greater than R
    • BIt will be less than R
    • CIt will be equal to R
    • DIt shall depend on the material of the road
    Answer: (B) It will be less than R
    Explanation

    Option b is the correct a car is at rest, the weight of the car is balanced normal reaction force from the road at each of the These forces are equal and act upwards. the car starts moving on a straight level road, forces come into play. The first is the driving by the engine to the rear wheels, which propels forward. The second is the friction force from the resists the motion of the here's the crucial part: the friction force is the normal reaction force at each wheel. As the this friction force increases. Since the is distributed differently over the wheels when it's the front wheels experience a decrease in the force compared to when the car was at rest. As the reaction at either of the front wheels will be what it was when the car was stationary. This is correct answer is (b) "It will be less than

12. #12UPSC CSE Prelims 2008
    Consider the following statements: Assertion (A): Radio waves bend in a magnetic field. Reason Radio waves are electromagnetic in nature. Code
    • ABoth (A) and (R) are true, and (R) is the correct explanation of (A)
    • BBoth (A) and (R) are true, but (R) is not the correct explanation of (A)
    • C(A) is true, but (R) is false
    • D(A) is false, but (R) is true
    Answer: (D) (A) is false, but (R) is true
    Explanation

    Option dis the correct (A) is false- Radio waves are but they do not bend in a magnetic field. This electromagnetic waves are made up of and magnetic fields, but the two fields to each other and to the direction of the wave. This means that electromagnetic waves do a net charge, and therefore they are not affected (R) is true- Radio waves are electromagnetic waves are a type of radiation that space at the speed of light. They are made up electric and magnetic fields

13. #13UPSC CSE Prelims 2008
    Consider the following statements: Assertion (A): In the visible spectrum of light, red light is more energetic than green light. Reason The wavelength of red light is more than that of green light. Code
    • ABoth A and Rare individually true, and R is the correct explanation of A
    • BBoth A and R are individually true, but R is not a correct explanation of A
    • CA is true, but R is false
    • DA is false, but R is true
    Answer: (D) A is false, but R is true
    Explanation

    Option d is the correct (A) is False: The energy of a photon of light proportional to its wavelength. In other with shorter wavelengths (like blue and violet) energy, while light with longer wavelengths (like green) has lower Q (R) is True: The wavelength of red light from approximately 620 to 750 nanometers the wavelength of green light typically ranges 495 to 570 nanometers (nm)

14. #14UPSC CSE Prelims 2003
    An oil tanker is partially filled with oil and moves forward on a level road with uniform acceleration. The free surface of oil then
    • ARemains horizontal
    • BIs inclined to the horizontal with smaller depth at the rear end
    • CIs inclined to the horizontal with larger depth at the rear end
    • DAssumes parabolic curve
    Answer: (C) Is inclined to the horizontal with larger depth at the rear end
    Explanation

    Option c is the correct answer. An oil tanker is partially filled with oil and moves forward a level road with uniform acceleration. The free surface of oil is inclined to the horizontal with larger depth at the rear end. This can be explained based on pseudo force on the oil molecules which acts in opposite direction of acceleration of the tanker. The free surface of the oil will be such that the tangential force on any fluid parcel is zero, since pressure is constant along the surface. Therefore, the component of the weight along the surface will be balanced by the component of the acceleration force along the surface. This implies that tan 0 a/g, where 0 is the angle of inclination and a is the acceleration of the tanker. Hence, the free surface of oil will be tilted by an angle 0 with respect to the horizontal, with larger depth at the rear

15. #15UPSC CSE Prelims 2002
    Consider the following statements: 1. Light of longer wavelength is scattered much more than the light of shorter wavelength. 2. The speed of visible light in water is 0.95 times the speed in vacuum. 3. Radio waves are produced by rapidly oscillating electrical currents. 4. To detect the over speeding vehicles, police use the Doppler effect of reflected short radio waves.Which of these statements are correct?
    • A1 and 2
    • B1 and 3
    • C2 and 4
    • D3 and 4
    Answer: (D) 3 and 4
    Explanation

    Option d is the correct l is incorrect: Shorter-wavelength light more because its smaller wavelengths interact with particles and obstacles in its path, causing scatter in various directions, while experiences less interference and scatters less. is known as Rayleigh 2 is incorrect: The speed of visible light in approximately 0.75 times the speed in a vacuum, not This reduction in speed is due to the higher of water (1.33), which causes light to slow down as through the mediuin} resulting in a lower 3 is correct: Radio waves are generated changing or oscillating electrical currents or transmitting devices. These oscillations waves that propagate through information in the form of modulated variations amplitude, frequency, or phase. Radio receivers decode these waves for communication or 4 is correct: Police use the Doppler effect short radio waves to detect speeding devices emit radio wa

16. #16UPSC CSE Prelims 2002
    Consider the following natural phenomena: 1. Terrestrial heating 2. Reflection of light 3. Refraction of light 4. Diffraction of light Due towhich of these phenomena is mirage formed?
    • A1 and 2 only
    • B2, 3 and 4 only
    • C1 and 3 only
    • D4 only
    Answer: (C) 1 and 3 only
    Explanation

    Option c is the correct are primarily formed due to two natural phenomena: Terrestrial heating: On hot days, the Earth's surface heats up, creating a temperature gradient near the ground. Refraction of light: This temperature gradient causes light to refract (bend) as it passes through layers of air with varying temperatures. As a result of refraction, the light can undergo total internal reflection, creating mirage-like optical illusions, typically seen as the appearance of water or pools on roads. Important Tips Diffraction of Light: Diffraction is a phenomenon in wave physics where waves, such as light, sound, or water waves, bend or spread out as they encounter an obstacle or pass through an aperture. Italian scientist Francesco Maria Grimaldi coined the term "diffraction" in 1660 and made accurate observations of the phenomenon. The Huygens-Fresnel principle, a fundamental concept i

17. #17UPSC CSE Prelims 2001
    Cloudy nights are warmer compared to dear cloudless nights, because douds
    • APrevent cold waves from the sky from descending on earth
    • BReflect back the heat given off by earth
    • CProduce heat and radiate it towards earth
    • DAbsorb heat from the atmosphere and send it toward earth
    Answer: (B) Reflect back the heat given off by earth
    Explanation

    Option b is the correct nights are warmer compared to dear because clouds act as insulators that trap the by the earth and prevent it from escaping This creates a greenhouse effect that keeps the warmer than it would be without clouds. nights, there is no cloud cover to reflect back so the earth loses more heat to the cold space and drops

18. #18UPSC CSE Prelims 2001
    Consider the following statements: Assertion (A): The boiling point of water decreases as the altitude increases. Reason The atmospheric pressure increases with altitude. Code
    • ABoth (A) and (R) are true, and (R) is the correct explanation of (A)
    • BBoth (A) and (R) are true, but (R) is not the correct explanation of (A)
    • C(A) is true, but (R) is false
    • D(A) is false, but (R) is true
    Answer: (C) (A) is true, but (R) is false
    Explanation

    Option c is the correct (A) is correct: The boiling point of as the altitude increases because the decreases with altitude. This means that the need less energy to escape into the gas phase, so the temperature at which the vapor pressure equals pressure is (R) is false: The atmospheric pressure depth, not with altitude. This is because the weight air above a given point decreases as the height increases

19. #19UPSC CSE Prelims 2000
    Fluorescent tubes are fitted with a choke. The choke coil
    • ASteps up the line voltage
    • BSteps down the line voltage
    • CReduces current in the circuit
    • DChokes low frequency current
    Answer: (A) Steps up the line voltage
    Explanation

    Option a is the correct A choke coil is essentially an inductor employed to flow of alternating current (AC) by storing a magnetic field. It operates by storing more its magnetic field as the circuit's cunent increases this stored energy back into the circuit as decreases, effectively smoothing out the AC and reducing undesirable low-frequency coils play a vital role in fluorescent tube they initially step up the line voltage to initiate the the necessary high voltage, and then subsequently to the tube's operating voltage. Also, they help maintain current flow through the fluorescent tube, which because these tubes are sensitive to fluctuations

20. #20UPSC CSE Prelims 2000
    Which one of the following does a TV remote control unit use to operate a TV set?
    • ALight waves
    • BSound waves
    • CMicrowaves
    • DRadio waves
    Answer: (D) Radio waves
    Explanation

    Option d is the correct remote controls utilize radio waves for the TV. When a button is pressed on the a small transmitter emits radio waves. The contains a receiver that captures these radio waves them to identify the specific button pressed

21. #21UPSC CSE Prelims 2000
    Consider the following statements: Assertion (A): A man standing on a completely frictionless surface can propel himself by whistling. Reason If no external force acts on a system, its momentum cannot change. Code
    • ABoth A and Rare true, and R is the correct explanation of A
    • BBoth A and R are true, but R is not a correct explanation of A
    • CA is true, but R is false
    • DA is false, but R is true orumim
    Answer: (A) Both A and Rare true, and R is the correct explanation of A
    Explanation

    Option a is the correct (A) is true: According to the law of momentum, if a person in a frictionless air in one direction while whistling, the experience an equal and opposite reaction due expulsion of air. This would propel the person in (R) is true: According to Newton's first motion, an object will remain in its state of rest motion in a straight line unless acted upon external force. In the absence of external forces, momentum of a system remains constant. The provides a correct explanation for the assertion (A), absence of external forces on the system allows to move in response to the force exerted by molecules when whistling. In the given scenario, is standing on a completely frictionless there are no external forces acting on the surroundings), the momentum of the remain constant

22. #22UPSC CSE Prelims 1999
    Consider the following statements: 1. If a person looks at a coin which is in a bucket of water, the coin will appear to be closer than it really is. 2. If a person underwater looks at a coin above the water surface, the coin will appear to be at a higher level than it really is.Which of the above statements is/ are correct?
    • A1 and 2 only
    • B1 only
    • C2 only
    • DNeither 1 nor 2 KING R. QUEEN P [ ]
    Answer: (A) 1 and 2 only
    Explanation

    Option a is the correct 1 is correct: When a person looks at a coin in of water, the light rays from the coin travel from the air, causing refraction. This bending of light coin appear to be at a shallower depth than its creating the illusion that it is closer than it This phenomenon is due to differences in the of water and 2 is incorrect: When a person underwater a coin above the water's surface, the coin actually be at a lower level, not higher level, than it actually is the bending of light at the water-air interface. This is known as refraction and causes objects to compared to their actual position. T depth I- Apparent depth Coin

23. #23UPSC CSE Prelims 1999
    Consider the following statements:An ordinary light bulb has a rather short life because the: 1. Filament wire is not uniform. 2. Bulb cannot be evacuated completely. 3. Wires supporting the filament melt at high temperatures.Which of the above statements are correct?
    • A1 and 3
    • B2 and 3
    • C1 and 2
    • D1, 2 and 3
    Answer: (D) 1, 2 and 3
    Explanation

    Option dis the correct 1 is correct- The filament wire is not means that some parts of the filament will heat than others. This uneven heating can cause to break more 2 is correct- The bulb cannot be This means that there will always be some inside the bulb. The air will react with the hot it to evaporate over 3 is correct- The wires supporting the at high temperatures. This can cause the filament and eventually break

24. #24UPSC CSE Prelims 1998
    The complete conversion of glucose, in the presence of oxygen, into carbon dioxide and water with release of energy is called
    • AAerobic respiration
    • BAnaerobic respiration
    • CGlycolysis
    • DHydrolysis
    Answer: (A) Aerobic respiration
    Explanation

    Option a is the correct respiration is the process of breaking in the presence of oxygen into carbon dioxide and releasing energy in the form of ATP. ATP is that stores and transfers energy for various Aerobic respiration occurs in the mitochondria cells and in the cytoplasm of prokaryotic cells. Important Tips Anaerobic respiration is the process of breaking down glucose in the absence of oxygen into different end products, such as ethanol, lactic acid, or hydrogen sulfide, and releasing less energy than aerobic respiration. Anaerobic respiration occurs in some bacteria, fungi, and animal cells under low oxygen conditions. Glycolysis is the first step of both aerobic and anaerobic respiration, where glucose is split into two molecules of pyruvate, and releasing a net gain of two ATP molecules and two NADH molecules. Glycolysis occurs in the cytoplasm of all living cells. Hydrolysis is t

25. #25UPSC CSE Prelims 1997
    Which one of the following is a vector quantity?
    • AMomentum
    • BPressure
    • CEnergy
    • DWork
    Answer: (A) Momentum
    Explanation

    Option a is the correct vector quantity is a physical quantity that has and direction. Momentum is the product of velocity, which are both vector quantities. is also a vector quantity. Pressure, energy are scalar quantities, which means they have and no direction. Important Tips The formula for momentum is given by where p is the momentum, m is the mass, and v is the velocity of the object. This formula shows that momentum is a vector quantity that depends on both the mass and the velocity of the object. The SI unit of momentum is kilogram meter per second (kg m/s)

26. #26UPSC CSE Prelims 1997
    Which one of the following is paramagnetic in nature?
    • AIron
    • BHydrogen
    • COxygen
    • DNitrogen
    Answer: (C) Oxygen
    Explanation

    Option c is the correct is paramagnetic because it has two in its outermost orbital. This means that are attracted to a magnetic field. is a material that is attracted to a magnetic field. Important Tips Paramagnetic Weakly attracted Aluminum, to a magnetic oxygen, titanium field Diamagnetic Weakly repelled Water, gold, by a magnetic copper field Ferromagnetic Strongly Iron, nickel, attracted to a cobalt magnetic field

27. #27UPSC CSE Prelims 1996
    Given below are two statements, one labelled as Assertion and the other labelled as Reason Assertion (A): Transformer is useful for stepping up or stepping down voltages. Reason Transformer is a device used in D.C. circuits. In the context of the above two statements, which one of the following is correct?
    • ABoth (A) and (R) are true, and (R) is the correct explanation of (A)
    • BBoth (A) and (R) are true, but (R) is not a correct explanation of (A)
    • C(A) is true, but (R) is false
    • D(A) is false, but (R) is true
    Answer: (C) (A) is true, but (R) is false
    Explanation

    Option c is the correct (A) is true- Transformers are used to step up down voltages in alternating current (AC) do this by using the principle of Electromagnetic induction is the production of across a conductor when it is exposed to a field. The magnitude of the induced voltage to the rate of change of the magnetic have two coiis of wire, a primary coil and coil. The primary coil is connected to the and the secondary coil is connected to the an alternating current flows through the primary creates a changing magnetic field. The changing induces an alternating current in the secondary (R) is false- Transformers are not used in (DC) circuits. DC current does not flow through because it does not create a changing

28. #28UPSC CSE Prelims 1996
    Domestic electrical wiring is basically a
    • ASeries connection
    • BParallel connection
    • CCombination of series and parallel connections
    • DSeries connection within each room and parallel connection elsewhere PYQ
    Answer: (B) Parallel connection
    Explanation

    Option b is the correct electrical wiring is basically a parallel are several advantages to using a parallel domestic electrical wiring: Individual Switching- Each appliance can be turned on and off independently of the other appliances. Appliances working independent of each other- If one appliance fails, the other appliances will continue to operate. Constant Voltage- The voltage and current delivered to each appliance is constant, regardless of how many other appliances are turned on

29. #29UPSC CSE Prelims 1996
    A simple machine helps a person in doing
    • ALess work
    • BThe same amount of work with lesser force
    • CThe same amount of work slowly
    • DThe same amount of work much faster
    Answer: (B) The same amount of work with lesser force
    Explanation

    Option b is the correct simple machine helps a person in doing the of work with lesser force. This is because a changes the direction or magnitude of a force mechanical advantage (also called leverage) to A lever can be used to lift a heavy object with by increasing the distance from the fulcrum to force. Some examples of simple machines are wheel and axle, screw, wedge and inclined plane. useful because they reduce effort or extend the people to perform tasks beyond their normal capabilities. Important Tips A simple machine is a mechanical device that changes the direction or magnitude of a force. A complex machine is a device that consists of two or more simple machines working together. Some differences between simple and complex machines are: Simple machines have few or no moving parts, while complex machines have many moving parts. Simple machines make work easier by reducing the fo

30. #30UPSC CSE Prelims 1995
    The variations in temperature from to with respect to time of two liquids Q are shown in the graph given below:Q p (0, 0) TimeWhich of the following statements is correct?
    • ADuring heating, liquid P has always warmer than Q
    • BAt no point of time during heating did the two liquids have the same temperature
    • CP attained the temperature of faster than Q
    • DQ attained the temperature of faster than P
    Answer: (D) Q attained the temperature of faster than P
    Explanation

    Option dis the correct per the graph, Q attained the temperature of than P. This means that Q has a higher rate of or in other words, Q has a lower specific than P. Specific heat capacity is the amount of required to raise the temperature of one unit a substance by one degree Celsius. A lower specific means that less heat energy is needed to increase of the substance. Therefore, Q reached than P because it required less heat energy to do a is incorrect: There is a point on the graph two curves intersect, which means that at that P and Q have the same temperature. Therefore, is not always warmer than b is incorrect: There is a point on the graph two curves intersect, which means that at that P and Q have the same temperature. Therefore, a point of time during heating when the two liquids same c is incorrect: If we look at the graph, we can see Preaches at a later time than curve Q. P atta

31. #31UPSC CSE Prelims 1995
    Which one of the following pairs of materials serve as electrodes in chargeable batteries commonly used in devices such as torchlights, electric shavers etc.?
    • ANickel and Cadmium
    • BZinc and Carbon
    • CLead peroxide and Lead
    • DIron and Cadmium
    Answer: (A) Nickel and Cadmium
    Explanation

    Option a is the correct and Cadmium are used as electrodes in commonly used in devices such as shavers, etc. Nickel-cadmium batteries are a P [. ] type of rechargeable battery that uses nickel and electrodes. batteries are relatively have a high energy density, making them a for a variety of applications. batteries are tolerant of overcharging and makes them a good choice for devices that are or irregularly. However, batteries have short lifespan, typically lasting for 500 to cycles

32. #32UPSC CSE Prelims 1995
    Which one of the following can be used to confirm whether drinking water contains a gamma emitting isotope or not?
    • AMicroscope
    • BLead plate
    • CScintillation counter
    • DSpectrophotometer
    Answer: (C) Scintillation counter
    Explanation

    Option c is the correct answer A scintillation counter is a highly sensitive device confirm the presence of gamma-emitting isotopes water or other substances. It operates by utilizing material that emits light when exposed to and a photodetector counts the emitted The quantity of light pulses directly correlates level of ionizing radiation detected, making ideal for accurately measuring even trace gamma radiation. Consequently, they are extensively applications like environmental monitoring and for their ability to ensure the safety and quality substances

33. #33UPSC CSE Prelims 1995
    When the same tone is played on a sitar and a flute, the sound produced can be distinguished from each other because of the difference in
    • Apitch, loudness, and quality
    • Bpitch and loudness
    • Cquality only
    • Dloudness only
    Answer: (C) quality only
    Explanation

    Option c is the correct the same tone is played on a sitar and a flute, and loudness of the sound produced will be the the quality of the sound will be different. This the two instruments have different different ways of producing sound. The sitar is a and the sound is produced when the strings The flute is a wind instrument, and the sound when the player blows into the mouthpiece

34. #34UPSC CSE Prelims 1995
    Suppose a Rocketship is proceeding from the earth at a speed of the velocity of light. A light in the Rocketship appears blue to the passengers on the ship. What colour would it appear to an observer on the earth?
    • ABlue
    • BOrange
    • CYellow
    • DYellow-Orange
    Answer: (C) Yellow
    Explanation

    Option c is the correct change in the color of light observed in this due to the relativistic Doppler effect. The is a phenomenon that causes the wavelength of change when the source of the light is moving relative observer. If the source of the light is moving observer, the wavelength of the will be shift). If the source of the light is moving the observer, the wavelength of the light will (red shift). As the rocketship moves away at a significant fraction of the speed of light, the inside the rocket experiences a redshift. To an Earth, this redshifted light would appear shifted longer wavelength region of the spectrum. This the wavelength of the light from the rocketship lengthened, and the light will appear yellow to on Earth

35. #35UPSC CSE Prelims 1995
    Optical fiber works on the principle of
    • ATotal internal reflection
    • BRefraction
    • CScattering
    • DInterference
    Answer: (A) Total internal reflection
    Explanation

    Option a is the correct fiber works on the principle of total Basie Operation of an Optical Fiber Light entering the fiber within this angular range will undergo total internal reflection and travel down the fiber. / Lower index cladding entering the fiber at higher angles will exit Total internal through the cladding. internal reflection occurs when light travels from medium to a less dense medium at an angle the critical angle. The critical angle is the angle at which the refracted ray is parallel to the total internal reflection occurs, all of the light back into the original fiber is a thin strand of glass or plastic that has high refractive index. The core of the optical fiber higher refractive index than the cladding, which is that surrounds the core. When light enters of the optical fiber, it is totally internally travels down the fibers can be used to transmit light signals over

36. #36UPSC CSE Prelims 1994
    The speed of light will be minimum while passing through
    • AGlass
    • BVacuum
    • CWater
    • DAir
    Answer: (A) Glass
    Explanation

    Option a is the correct speed of light is maximum in a vacuum and a denser medium like glass. When light travels material, such as glass or water, it slows down. This the light interacts with the atoms and the material. The amount that the light slows on the refractive index of the material. index of a material is a measure of how much light. Glass has a higher refractive index than air This means that light slows down more when it glass than when it travels through air or water. the medium, the more the light interacts with it, the slower it travels. Therefore, the speed of light while passing through glass. Important Tips Refractive Index: Refractive index is a dimensionless quantity that describes the behavior of light as it passes through a material. When light travels from one medium to another, it changes direction due to the change in speed of light in the two media. The refractiv

37. #37UPSC CSE Prelims 1994
    A glass bottle containing water and tightly dosed, breaks when it is kept in freezer, because
    • ABottle shrinks on freezing
    • BThe volume of water decreases on freezing
    • CThe volume of water increases on freezing
    • DGlass is the bad conductor of heat
    Answer: (C) The volume of water increases on freezing
    Explanation

    Option c is the correct answer. A glass bottle containing water and tightly corked breaks when it is kept in freezer, because the volume of watel" increases on freezing. Water has a unique molecular structure, where one oxygen atom bonds with two hydrogen atoms. The oxygen atom is slightly negative, and the hydrogen atoms are slightly positive, so they form hydrogen bonds with other water molecules. When water freezes, the molecules arrange themselves in a crystalline structure that has more space between them than in liquid form. This makes ice less dense and more voluminous than water. Therefore, when a glass bottle containing water is tightly corked and kept in a freezer, the water inside expands as it freezes and exerts pressure on the glass, causing it to break

38. #38UPSC CSE Prelims 1994
    The colour of an opaque object is due to the colour it
    • AAbsorbs
    • BRefracts
    • CReflects
    • DScatters
    Answer: (C) Reflects
    Explanation

    Option c is the correct answer. The color of an opaque object is due to the color it reflects. When light hits an opaque object, some of the light is absorbed and some of the light is reflected. The color of the object is determined by the color of light that is reflected. For example, a red object reflects red light and absorbs all other colors of light. A white object reflects all colors of light and absorbs no light. A black object absorbs all colors of light and reflects no light. Since it reflects no light it has black colour

39. #39UPSC CSE Prelims 1994
    Normally the pitch of females are
    • AMore than that of males
    • BSlightly low than that of males
    • CVery low than that of males
    • DExactly same as that of males
    Answer: (A) More than that of males
    Explanation

    Option a is the correct pitch or shrillness of voice is determined by of the sound waves produced by the vocal higher frequency corresponds to a higher pitch, while frequency results in a lower pitch. Typically, the of females are shorter and thinner than those This anatomical difference leads to faster the vocal cords in females, resulting in a The average pitch of a female voice falls in the 165 to 255 hertz (Hz), while the average pitch of a is approximately 85 to 155 Hz. Therefore, the pitch is generally higher than that of males

40. #40UPSC CSE Prelims 1993
    The formation of glittering colours in thin foam of soap is the result of which of the following phenomenon
    • ATotal reflection and interference
    • BTotal refraction and dispersion
    • CDiffraction and dispersion
    • DPolarization and interference Other Examination Previous Years' Qu.estion
    Answer: (A) Total reflection and interference
    Explanation

    Exp) Option a is the correct answer. P [ ] The formation of glittering colors in thin foam of soap result of total reflection and interference of reflection: Total Internal reflection is involved in of glittering colors in thin soap film because the iight waves to travel through the film before being reflected back. This increases that the light waves travel and allows for to When light shines on a thin film of soap, is reflected from both the front and back surfaces of The two reflected waves interfere with each other, color of the light that is seen depends on the the film. If the film is thick enough, the two will destructively interfere, and all of the light will out. However, if the film is thin enough, the waves will constructively interfere, and of light will be seen. The different colors that in soap foam are due to the different thicknesses film. The thicker parts of the film wi

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