Day-762 | Daily MCQs | UPSC Prelims | SCIENCE AND TECHNOLOGY

Answer: B
Explanation:
Transverse waves cause the medium to move perpendicular to the direction of the wave.
Longitudinal waves cause the medium to move parallel to the direction of the wave.
• Example 1 is CORRECT: When a stone is thrown into a pond, it creates ripples on the surface of the water. It is a transverse wave because the water molecules move up and down but the wave move forward.
• Example 2 is CORRECT: Wave on string or rope is an example of transverse wave. This is because the string is moved in the direction which is perpendicular to the movement of the wave generated.
• Example 3 is INCORRECT: Compression and rarefaction in spring is a longitudinal wave because the compression and relaxation in spring happen along the length of the spring which is also the wave direction of vibration.

Answer: A
Explanation:
Friction is the force that resists motion when the surface of one object comes in contact with the surface of another. There are 3 types of friction in nature
I. Static friction
II. Sliding friction
III. Rolling friction
Frictional force depends upon 3 factors:
1. Weight of an object under consideration
2. Nature of interacting surface
3. Area of contact
• Both Statements are CORRECT and Statement 2 is the CORRECT explanation of Statement 1
• Statement 1 is CORRECT: It is easier to roll an object that to slide it because rolling friction is less than sliding friction.
• Statement 2 is CORRECT and is the correct explanation of statement 1: Frictional force is directly proportional to the area of contact. The area of contact is more in case of sliding friction as compared to rolling friction which has a very less contact area. So, rolling friction is less than sliding friction.

Answer: B
Explanation:
• Both Statements are correct, But Statement 2 is NOT the correct explanation of Statement 1.
• Statement 1 is CORRECT: An induction compatible cooking vessel must be made of, or contain, a ferrous metal such as cast iron or some stainless steels. The iron in the pot concentrates the current to produce heat in the metal. If the metal is too thin, or does not provide enough resistance to current flow, heating will not be effective.
• Statement 2 is CORRECT but is NOT the CORRECT explanation of Statement 1: It works on the principle of Electromagnetic Induction. But Electro Magnetic Induction is also shown by other metals like copper and aluminium, but Induction tops typically will not heat copper or aluminum vessels because the magnetic field cannot produce a concentrated current. That is why induction compatible utensils have an electroplating of cast iron at the bottom. So, the correct explanation is the concentration of current to produce heat in the metal.

Answer: B
Explanation:
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. It works on the principle of magnetic effects of electric current.
• Example 1 is CORRECT: A loudspeaker is composed of a permanent magnet, an electromagnet, and a vibrating cone. Electricity flowing through coils of wire create an electromagnet. This electromagnet is attached to the cone. As current flows through the coils of wire the electromagnet that is created is quickly pulled towards the permanent magnet and then quickly repelled from it taking the cone with it. As the cone vibrates it creates pulses of air that form sound waves.
• Example 2 is CORRECT: The choke’s core function is to obstruct or ‘choke’ high-frequency signals. It uses electromagnetic induction and the characteristics of inductive reactance. A choke comprises a coil of insulated wire often wound on a magnetic core. When AC passes through this coil, it creates a magnetic field around it. This magnetic field then induces a back EMF (electromotive force) in the coil, opposing changes in the coil’s current.
• Statement 3 is INCORRECT: An LED bulb produces light by passing the electric current through a semiconducting material—the diode—which then emits photons (light) through the principle of electroluminescence.

Answer: A
Explanation:
The phenomenon of splitting of visible light into its component colours is called dispersion. Dispersion of light is caused by the change of speed of light ray (resulting in angle of deviation) of each wavelength by a different amount whereas scattering is the phenomenon due to which the light ray deviates from its original path in a different direction.
• 1st Phenomenon is INCORRECT: Blue colour of the sky is due to scattering of light. The two most common types of matter present in the atmosphere are gaseous nitrogen and oxygen. These particles are most effective in scattering the higher frequency and shorter wavelength portions (or blue region) of the visible light spectrum.
• 2nd Phenomenon is INCORRECT: Red has the longest wavelength of any visible light, the sun is red when it’s on the horizon, where it’s extremely long path through the atmosphere blocks all other colours. This happens due to scattering of light of lower wavelength in the blue region of the visible spectrum.
• 3rd Phenomenon is CORRECT: Formation of rainbow is due to dispersion of light. A rainbow is a natural spectrum appearing in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally, refract it again when it comes out of the raindrop. Due to the dispersion of light and internal reflection, different colors reach the observer’s eye. Examples of dispersion in daily life:
o Rainbow formation
o Petrol poured on water will show different colours.
o Prism splits the light into different colours on passing through it.
o Dispersion of colours in soap bubbles.
o Dispersion of colours on CDs.
o Dispersion could be seen from plastic scales.

Answer: C
Explanation:

The excretory system of human beings includes a pair of kidneys, a pair of ureters, a urinary bladder and a urethra.
• Statement 1 is INCORRECT: There are basically three types of wastes generated in the human body – gases, faecal matter and nitrogenous wastes. Gases like carbon dioxide are removed through exhalation – a part of respiratory system. Faecal matters are removed through anus by egestion – last part of the digestive system. The human excretory system is involved in the removal of nitrogenous wastes like urea or uric acid and creatinine from the human blood.
• Statement 2 is INCORRECT: The purification of blood happens through a process known as osmosis. For kidneys, it is known as Glomerular filtration. This forms urine which is a mixture of excess fluid waste from the blood as well as other nitrogenous wastes.

Answer: A
Explanation:
Blood is made up of broadly 4 components – Blood plasma, Red Blood Cells (RBCs), White Blood Cells (WBCs) and the platelets.

• Statement 1 is INCORRECT: Thrombocytes or the platelets help with blood clotting after an injury.
• Statement 2 is CORRECT: Leukocytes or the White Blood Cells help fight infection and disease. White blood cells include lymphocytes, which make up the cornerstone of the immune system, and myeloid cells, which include granulocytes, neutrophils, monocytes, eosinophils, and basophils.
• Statement 3 is INCORRECT: Erythrocytes or the Red Blood Cells transport oxygen around the body.

Answer: C
Explanation:
• Statement 1 is CORRECT: Nasal congestion changes the flavour of the food. This is because flavour is a combination of taste and smell. Excess mucus formation blocks the nasal pathway.
• Statement 2 is INCORRECT: Nasal congestion does not alter the taste buds, but it reduces the smelling capacity of affected person. There are only five tastes: salty, sweet, sour, bitter, and savory. Compared to taste, there are a virtually unlimited number of scents humans can detect. Therefore, when our nose is blocked, we can only “taste” the food and are unable to “smell”, missing most of food’s flavour. This is why one feels a bad taste when one catches cold and flu.

Answer: A
Explanation:
• Both Statements are CORRECT and Statement 2 is the CORRECT explanation of Statement 1.
• Statement 1 is CORRECT: Every organism responds to stimulus. But in case of reflex action, the response is quick as stimulus is perceived as more dangerous or sometimes life-threatening. To quickly respond to the stimuli, reflex arc comes into action. It is a connection that directly links the receptors in sense organs like skin which senses a stimuli like heat, and effectors in muscles to which is signalled by the spinal cord to quickly respond by removing the hands from the source of heat.
• Statement 2 is CORRECT and is the CORRECT explanation of statement 1: Thinking is a complex activity which requires divergent and convergent neural activity. This is rather a slow process which is carried out in various parts of the brain. But reflex action requires quick response. So, a smaller pathway has been created, passing through the spinal cord where receptors and effectors signals meet before they are relayed to the brain.

Answer: D
Explanation:
Phototropism is a directional response that allows plants to grow towards, or in some cases away from, a source of light. Photoperiodism is the regulation of physiology or development in response to day length.
• Statement 1 is CORRECT: Movement of sunflower towards the sun is an example of phototropism. The growth increases in the shoots of the sunflower that is away from sunlight, causing the plant to bend towards the sun’s direction.
• Statement 2 is CORRECT: The relative length of day and night is known as photoperiod. Some plants need to be exposed to sunlight for a particular duration of time to induce flowering. This is the reason behind the seasonal blooming of flowers, and it is known as photoperiodism.

Answer: D
Explanation:
The Human Eye

The human eye is like a camera.
Pupil – It regulates and controls the amount of light entering the eyes.
Cornea – It is the clear, dome-shaped window of the front of the eye. It focuses light into the eye.
Iris – It is the colour part of the eye and a muscular diaphragm that controls the size of the pupil.
Retina – Retina is like a film where image is formed. It is a delicate membrane having enormous light sensitive cells which send signals to brain via the optic nerve.

Answer: D
Explanation:
• Statement 1 is INCORRECT: Concave lens of suitable power is used to correct myopia. A person with myopia can see the nearby objects clearly but cannot see distant objects distinctly. The defect may arise due to excessive curvature of the eye lens or elongation of the eyeball.
• Statement 2 is INCORRECT: A person with hypermetropia can see the distant objects clearly but cannot see nearby objects distinctly. This can arise if the focal length of the eye lens is too long, or the eyeball has shrunk. Convex lens of suitable power is used to correct hypermetropia.
• Statement 3 is INCORRECT: Cylindrical lens is used to correct astigmatism. Astigmatism is an imperfection in the curvature of the eye’s cornea or lens. With astigmatism the vision is blurry at all distances.

Answer: C
Explanation:
A gyroscope is a device used for measuring or maintaining orientation and angular velocity. This feature is used in electronic devices through mini gyroscopic sensors which are embedded in the chips of those electronic devices.

• 1st device is CORRECT: Gyroscopes have been used in virtual reality headset and other VR products for many years. Several miniature gyroscope sensors are placed in the headset. Whenever the user moves their head the direction and speed are sent back to the computer. The computer can then change the display as required.
• 2nd device is CORRECT: There are a number of computer pointing devices that have gyroscopes inside them allowing the user to control the mouse cursor. They are also wireless and are used for presentations when the speaker is moving around the room. The gyroscope inside tracks the movements of the hand and translates them to cursor movements.
• 3rd device is CORRECT: High-end earpods like the Apple Airpods Pro uses built-in gyroscopes and accelerometers to track movement of the user’s head and provide theatre-like surround sound experience.

Answer: A
Explanation:
Inertia is the inherent property of a body that makes it oppose any force that would cause a change in its motion.
• 1st Example is INCORRECT: A fast moving ball tends to keep moving due to momentum. But to reduce the speed of the ball, the hands are pulled back to reduce momentum without hurting the hands. Thus, it is a manifestation of law of conservation of momentum and not inertia.
• 2nd Example is CORRECT: When the car turns around the corner, our body tries to continue in the same path that it was originally on and so we shift within the car. This happens due to inertia.
• 3rd Example is INCORRECT: Self balancing of a spinning top is due to gyroscopic couple. Spinning tops are a simple form of gyroscope, as the spinning top is rotated it can stand up right without falling over due to its gyroscopic behaviour.

Answer: A
Explanation:
Reverberation is the repeated reflection of sound that results in its persistence.

• Both Statements are CORRECT and Statement 2 is the CORRECT explanation of Statement 1.
• Statement 1 is CORRECT: Ceiling of concerts or cinema halls are made in a curved shape to use multiple reflection of sound known as reverberation.
• Statement 2 is CORRECT and is the CORRECT explanation of Statement 1: The curved ceiling of the hall uses the reverberation feature of sound so that sound after reflection reaches all corners of the hall giving surround sound effects.

Answer: D
Explanation:
Plants send signals for growth and activity through various plant hormones. These are chemical compounds present in very low concentration in plants.
• Pair 1 is INCORRECT: Auxin helps in shoots to grow longer. When growing plants detect light, auxin diffuses to the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards the light.
• Pair 2 is INCORRECT: Cytokinin promotes cell division. Thus, they are present in greater concentration in areas of rapid cell division such as fruits and seeds.
• Pair 3 is INCORRECT: Abscisic acid inhibits growth. It does so by counteracting the hormones that promote the growth of plants. The other functions of this hormone are maintaining seed dormancy, causing wilting of leaves, etc.

Answer: B
Explanation:
There are 2 ways of information transmission from organs to brain and back to the organs – Through neuron firing which creates electrical impulses and through release of chemical hormones.
• Both Statements are CORRECT and Statement 2 is NOT the CORRECT explanation of Statement 1.
• Statement 1 is CORRECT: Electrical impulses are faster than chemical hormones because electrical impulses have dedicated pathway in terms of neural structure which connects the control centre (brain) with maximum parts of the body. This is not present in case of hormone-based transmission since the release lack a clear pathway or link for communication.
• Statement 2 is CORRECT but is NOT the CORRECT explanation of Statement 1: Since there are linkages with various part of the body, there is a relatively limited reach as compared to chemical hormone release. Moreover, chemical hormones diffuse throughout the body and only those cells get activated which have specific detectors for the chemical compound.

Answer: D
Explanation:
The municipal wastewater which contains excreta of humans are called as sewage. They cannot be released directly into the water bodies as they have large amounts of harmful microbes and organic matter. Thus, they are firstly treated in sewage treatment plants (STPs) to make it less polluting.
• Statement 1 is CORRECT: The treatment in STPs is carried out in two phases – Primary treatment and Secondary treatment. Primary treatment is basically a physical process of removal of large and small particles from the sewage through filtration and sedimentation. Secondary treatment involves growth of microbes to decompose the organic matter and thus, is a biological process.
• Statement 2 is CORRECT: As the microorganisms consume the significant amount of organic matter in the effluent, this reduces the Biological Oxygen Demand (BOD) of the effluent. BOD refers to the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria.

Answer: A
Explanation:
In the diversity of Plant kingdom, those plants which produce seeds are classified as Phanerograms. Phanerograms are further classified into Angiosperms and Gymnosperms.
• Statement 1 is CORRECT: Angiosperms are also known as flowering plants. The seeds develop inside an ovary which is modified to become a fruit.
• Statement 2 is INCORRECT: Gymnosperms also produce seeds but, they bear naked seeds and are usually perennial, evergreen and woody. Example – pine and deodar.

Answer: B
Explanation:
In Angiosperms, flowers are referred to as reproductive parts. They constitute the female as well as the male reproductive structures respectively. Sexual reproduction in plants takes place with the help of these reproductive structures.

• The stamen is the male reproductive organ. It consists of a pollen sac (another) and a long supporting filament. This filament holds the anther in position, making the pollen available for dispersal by wind, insects, or birds.
• Carpels are the basic units of the female reproductive system of a flower. Each carpel includes the following parts:
o Stigma: Receives pollen during pollination.
o Style: A stalk that connects stigma to ovary.
o Ovary: Contains ovules which are the female reproductive cells (egg cells).
• Part 1 is CORRECT: Style is a part of female reproductive structures of plants.
• Part 2 is INCORRECT: Filament is a part of male reproductive structures of plants.
• Part 3 is CORRECT: Stigma is a part of female reproductive structures of plants.
Source: NCERT class 12 Biology