Physics Archives

141. Match List I with List II and select the correct answer using the code

Match List I with List II and select the correct answer using the code given below the Lists :

List I (Explanation)	List II (Term)
A. Colour of an opaque object	1. Fluorescence
B. Colour observed through a coloured glass	2. Reflection
C. Bending of the image of a rod partially dipped in water	3. Transmission
D. Shining observed when one steps on an earthworm	4. Refraction

[amp_mcq option1=”1 3 4 2″ option2=”1 4 3 2″ option3=”2 4 3 1″ option4=”2 3 4 1″ correct=”option4″]

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UPSC CAPF – 2014

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Let’s match the explanations with the terms:
A. Colour of an opaque object: Opaque objects get their colour by absorbing certain wavelengths of light and reflecting others. The colour we see is the colour of the light reflected by the object. This matches term 2. Reflection.
B. Colour observed through a coloured glass: Coloured glass allows certain wavelengths of light to pass through while absorbing others. The colour we see is the colour of the light transmitted through the glass. This matches term 3. Transmission.
C. Bending of the image of a rod partially dipped in water: This phenomenon occurs because light changes speed as it passes from one medium (air) to another (water), causing it to bend at the interface. This bending of light is called refraction. This matches term 4. Refraction.
D. Shining observed when one steps on an earthworm: With A, B, and C matched to 2, 3, and 4 respectively, the remaining term for D is 1. Fluorescence is the emission of light by a substance after it has absorbed light. While shining can often be explained by reflection, it is possible that some biological substances exhibit fluorescence. Given the other standard matches, this is the most likely intended pairing in the context of the question’s options.
Matching: A-2, B-3, C-4, D-1. This corresponds to option D.

Understand basic optical phenomena: Reflection (light bouncing off a surface), Transmission (light passing through a substance), Refraction (bending of light as it passes from one medium to another), and Fluorescence (emission of light after absorbing radiation). Apply these concepts to everyday observations.

While “shining” is most commonly associated with reflection, the options force a match with Fluorescence for the last item. It’s possible the question refers to a specific, perhaps less common, property of earthworm mucus or tissues under certain conditions, or it might be a less precise pairing designed within the options provided. However, the matches for A, B, and C are definitive.

142. Large Hadron Collider was in news recently for doing some scientific r

Large Hadron Collider was in news recently for doing some scientific research to prove the presence of an elementary particle. The scientist who predicted this particle in 1964 has been awarded Nobel Prize in 2013. What is this discovery ?

[amp_mcq option1=”Particles known as quarks having mass” option2=”Origin of Universe timings” option3=”Bigg’s Bosons or God Particles explaining why fundamental particles have mass” option4=”None of the above” correct=”option3″]

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The question describes the search and discovery of the Higgs boson at the Large Hadron Collider (LHC) at CERN, which was heavily in the news, leading to the 2013 Nobel Prize in Physics awarded to François Englert and Peter Higgs who had theorized its existence in 1964.

The Higgs boson is an elementary particle associated with the Higgs field. This field is thought to be present throughout the universe, and interactions with it give other fundamental particles (like quarks and leptons) their mass. It is often popularly referred to as the “God particle”.

– Quarks are fundamental particles that are components of protons and neutrons; they do have mass, but the Higgs mechanism explains *why* they have mass, not just that they do.
– The origin of the universe timings is related to cosmology and the Big Bang theory, not the Higgs boson discovery.
– The LHC is the world’s largest and most powerful particle accelerator, used to collide beams of protons or heavy ions at high energies to study fundamental particles and forces.

143. The weight of any object is felt due to gravity of Earth. When any obj

The weight of any object is felt due to gravity of Earth. When any object goes inside the Earth or above the Earth, weight decreases. It will weigh minimum when an object is placed at :

[amp_mcq option1=”The Equator and Moon” option2=”North Pole and Saturn” option3=”South Pole and 1 Km beneath the Earth” option4=”Centre of Earth and in an orbiting satellite” correct=”option4″]

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The weight of an object is given by W = mg, where m is its mass and g is the acceleration due to gravity. The acceleration due to gravity varies with location.

At the center of the Earth, the acceleration due to gravity (g) is zero because the gravitational forces from all parts of the Earth cancel out. In an orbiting satellite, an object is in a state of continuous freefall around the Earth, resulting in apparent weightlessness, which means the object feels minimum (essentially zero apparent) weight.

– Gravity is maximum on the Earth’s surface. It decreases as you move away from or towards the center (until the center).
– On the surface, gravity is slightly higher at the poles than at the equator due to Earth’s shape (oblate spheroid) and centrifugal force from rotation.
– The Moon has about 1/6th the gravity of Earth’s surface, but gravity is not zero.
– Saturn has a different and much stronger gravitational field compared to Earth.
– 1 km beneath the Earth’s surface, gravity has slightly decreased but is still significant.

144. If a scientist reads an ambient temperature 273 K in the laboratory, w

If a scientist reads an ambient temperature 273 K in the laboratory, what will a doctor’s thermometer read it ?

[amp_mcq option1=”0 degree Fahrenheit” option2=”32 degrees Fahrenheit” option3=”99 degrees Fahrenheit” option4=”– 100 degrees Fahrenheit” correct=”option2″]

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The correct answer is 32 degrees Fahrenheit.

To convert temperature from Kelvin (K) to Fahrenheit (°F), we first convert Kelvin to Celsius (°C) and then Celsius to Fahrenheit.
The formula for converting Kelvin to Celsius is:
°C = K – 273.15
Given temperature is 273 K.
°C = 273 – 273.15 = -0.15 °C.
However, in many contexts, 273 K is treated as approximately 0°C, especially in simplified problems like this. Let’s use 0°C.

The formula for converting Celsius to Fahrenheit is:
°F = (°C × 9/5) + 32
Using °C = 0:
°F = (0 × 9/5) + 32
°F = 0 + 32
°F = 32.

So, 273 K is equivalent to 32°F. This corresponds to the freezing point of water.

The exact freezing point of water is 273.15 K or 0°C or 32°F. The value 273 K is a common approximation used in many problems.

145. According to the principle of energy conservation, when a piston in an

According to the principle of energy conservation, when a piston in an automobile engine compresses the gas in a cylinder, which of the following must occur ?

[amp_mcq option1=”Kinetic energy of gas must increase” option2=”The gas must undergo a change of state” option3=”The gas must undergo a chemical change” option4=”None of the above” correct=”option1″]

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When a piston compresses the gas in a cylinder, work is done on the gas. According to the principle of energy conservation (specifically the First Law of Thermodynamics), this work done on the gas increases its internal energy. For an ideal gas, internal energy is directly related to its temperature, and temperature is a measure of the average kinetic energy of the gas molecules. Therefore, the kinetic energy of the gas must increase.

Work done *on* a system (like compressing gas) increases its internal energy. Increased internal energy in a gas manifests as increased temperature and thus increased average kinetic energy of the molecules.

Compression can lead to a change of state or chemical change under specific conditions (e.g., if the pressure and temperature exceed certain thresholds, or if the compression causes ignition in a fuel mixture). However, an increase in internal energy and kinetic energy is a direct and necessary consequence of work being done *on* the gas during compression, based purely on the principle of energy conservation.

146. What is the correct sequence of conductivity when arranged in ascendin

What is the correct sequence of conductivity when arranged in ascending order?

[amp_mcq option1=”Metals, semiconductors, insulators” option2=”Insulators, metals, semi-conductors” option3=”Semiconductors, metals, insulators” option4=”Insulators, semiconductors, metals” correct=”option4″]

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D) Insulators, semiconductors, metals

Electrical conductivity is a measure of a material’s ability to conduct electric current. Materials are classified based on their conductivity:
– Insulators have very low conductivity, resisting the flow of charge (e.g., rubber, plastic, glass).
– Semiconductors have conductivity between that of insulators and conductors, which can be significantly altered by temperature, doping, or external fields (e.g., silicon, germanium).
– Metals (conductors) have high conductivity, allowing charge to flow easily (e.g., copper, silver, gold).
Arranging these in ascending order of conductivity means starting from the lowest conductivity to the highest. Therefore, the correct sequence is Insulators < Semiconductors < Metals.

The conductivity of materials is related to the availability of free charge carriers (electrons or ions) within their structure and how easily these carriers can move. In metals, there is a large number of free electrons. In semiconductors, the number of free carriers is much smaller but can be increased. Insulators have very few free charge carriers.

147. The formation of colours in soap bubbles is due to the phenomenon of

The formation of colours in soap bubbles is due to the phenomenon of

[amp_mcq option1=”dispersion of light” option2=”interference of light” option3=”diffraction of light” option4=”polarization of light” correct=”option2″]

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B) interference of light

The iridescent colours observed in soap bubbles are a result of the interference of light waves. When light strikes the thin soap film, it reflects off both the outer and inner surfaces. These two reflected waves interfere with each other. Due to the slight difference in the path length traveled by the waves (determined by the thickness of the film and the angle of incidence) and the phase change upon reflection, certain wavelengths of light are constructively interfered (enhanced), while others are destructively interfered (cancelled). This results in the appearance of vibrant colours, which vary depending on the local thickness of the soap film.

This phenomenon is also observed in other thin films, such as oil slicks on water. The specific colour seen at any point on the bubble depends on the thickness of the film at that point and the angle from which it is viewed. As the soap bubble thins (e.g., due to evaporation), the colours change, often displaying white or black just before bursting when the film becomes extremely thin.

148. Advanced sunrise and delayed sun-set found in the sky are due to the p

Advanced sunrise and delayed sun-set found in the sky are due to the phenomenon of

[amp_mcq option1=”diffraction of sunlight” option2=”refraction of sunlight” option3=”scattering of sunlight” option4=”total internal reflection of sun-light” correct=”option2″]

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The correct option is B. Advanced sunrise and delayed sunset are due to the phenomenon of refraction of sunlight.

As sunlight enters the Earth’s atmosphere, it passes through layers of air with varying densities. This causes the light rays to bend, or refract. Near the horizon, where sunlight travels through a larger amount of atmosphere, this refraction is significant. The atmosphere bends the light rays downwards, towards the Earth’s surface. This bending makes the Sun appear higher in the sky than its actual position. As a result, we see the Sun before it has actually risen above the horizon (advanced sunrise) and after it has actually set below the horizon (delayed sunset).

Refraction causes the apparent position of the Sun to be about 0.5 degrees higher than its true position when it is near the horizon. This leads to sunrise appearing about two minutes earlier and sunset about two minutes later than they would in the absence of atmospheric refraction. Diffraction is the bending of light around obstacles. Scattering is the redirection of light by particles. Total internal reflection requires specific conditions involving light moving from a denser to a rarer medium.

149. The filament of electric bulb is generally made of tungsten because

The filament of electric bulb is generally made of tungsten because

[amp_mcq option1=”tungsten is cheap” option2=”durability of tungsten is high” option3=”light-emitting power of tungsten is high” option4=”melting point of tungsten is high” correct=”option4″]

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The correct option is D. The filament of an electric bulb is generally made of tungsten because its melting point is high.

Incandescent light bulbs produce light by heating a wire filament to a very high temperature (around 2500-3000 °C) until it glows (incandescence). Tungsten has the highest melting point of all metals (3422 °C), allowing it to withstand these extreme temperatures without melting. This property is crucial for the filament’s operation.

While tungsten is durable and emits light, its high melting point is the primary reason for its use as a filament material. Other properties like its low vapor pressure at high temperatures also contribute to its suitability, reducing evaporation and prolonging filament life compared to materials with lower melting points. Tungsten is not particularly cheap compared to common metals.

150. Transformer is used to 1. convert low a.c. voltage to high voltage

Transformer is used to

1. convert low a.c. voltage to high voltage
2. convert high a.c. voltage to low voltage
3. convert direct current to alternating current
4. regulate the fluctuation of voltage

Select the correct answer using the code given below.

[amp_mcq option1=”1 only” option2=”2 only” option3=”1 and 2″ option4=”3 and 4″ correct=”option3″]

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The correct option is C. A transformer is used to convert low a.c. voltage to high voltage and convert high a.c. voltage to low voltage.

Transformers are electrical devices that transfer electrical energy between two or more circuits through electromagnetic induction, typically to change the voltage level. A step-up transformer converts a low AC voltage to a high AC voltage (statement 1), while a step-down transformer converts a high AC voltage to a low AC voltage (statement 2). Transformers only work with alternating current (AC).

Statement 3 is incorrect; converting direct current (DC) to alternating current (AC) is done by an inverter. Statement 4 is incorrect; regulating voltage fluctuations is the function of voltage regulators or stabilizers, although transformers are part of the power distribution system where voltage levels are managed.