General Science - Physics MCQs

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The above all four options are correct because Earth is not an exactly spherical body.

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Human audible range is from 12-16 Hz to 20000 Hz. In Dogs, it is within the range of approximately 40 Hz to 60,000 Hz. The Dog whistles are blown at around 220000-25000 Hz, which seem silent to us but can bring a dog in action, thus used in their training. Bats use the concept of echolocation and their frequency range is between 20 Hz and 120,000 Hz. Dolphins range anything between 0.25 to 150 kHz.

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Ultrasounds are high frequency waves. Ultrasounds are able to travel along well defined paths even in the presence of obstacles.

• Ultrasounds are used extensively in industries and for medical purposes. Ultrasound is generally used to clean parts located in hard-to-reach places, for example, spiral tube, odd shaped parts, electronic components etc. Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to the high frequency, the particles of dust, grease and dirt get detached and drop out. The objects thus get thoroughly cleaned.
• Ultrasounds can be used to detect cracks and flaws in metal blocks. Metallic components are generally used in construction of big structures like buildings, bridges, machines and also scientific equipment. The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure. Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect.
• Ordinary sound of longer wavelengths cannot be used for such purpose as it will bend around the corners of the defective location and enter the detector.
• Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.
• Ultrasound scanner is an instrument which uses ultrasonic waves for getting images of internal organs of the human body. A doctor may image the patient’s organs such as the liver, gall bladder, uterus, kidney, etc. It helps the doctor to detect abnormalities, such as stones in the gall bladder and kidney or tumours in different organs. In this technique the ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density.

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Excerpt from NCERT Class IX Science. How the brain interprets the frequency of an emitted sound is called its pitch. The faster the vibration of the source, the higher is the frequency and the higher is the pitch. Thus, a high pitch sound corresponds to more number of compressions and rarefactions passing a fixed point per unit time. Objects of different sizes and conditions vibrate at different frequencies to produce sounds of different pitch. The loudness or softness of a sound is determined basically by its amplitude. The amplitude of the sound wave depends upon the force with which an object is made to vibrate. If we strike a table lightly, we hear a soft sound because we produce a sound wave of less energy (amplitude). If we hit the table hard we hear a loud sound. Can you tell why? Loud sound can travel a larger distance as it is associated with higher energy. A sound wave spreads out from its source. As it moves away from the source its amplitude as well as its loudness decreases.

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With the continuous change in direction there is change in velocity and acceleration.
 

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 A quantity which depends on direction is called a vector quantity. A quantity which does not depend on direction is called a scalar quantity. Entropy and work are scalar quantities.
 

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When radio waves enter into the Earth atmosphere from space some of the waves are absorbed by the electrons present in the ionosphere. Some of the waves are reflected and some of them face diffraction and diffraction due to differently dense medium of Earth atmosphere.

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All metals are good conductors of heat because they contain free electrons so the transfer of heat becomes easy and the molecules in them are very close to each other so the heat transfer becomes more efficient.

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A CD or DVD has closely spaced tracks which work as a diffraction grating to form the familiar rainbow pattern seen when looking at a disk.

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Gravity plays a role in flame formation. Modifying the gravity causes different flame types. The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a general flame, as in a candle in normal gravity conditions, making it yellow. In micro gravity or zero gravity, such as an environment in outer space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although it may go out if not moved steadily, as the CO2 from combustion does not disperse as readily in micro gravity, and tends to smother the flame).