General Science - Physics MCQs

Notes:
A photograph can be recorded using lens and normal light sources but in case of holography, laser is required and the light from the object is scattered directly onto the recording medium. After cutting of a photograph, each piece shows half of the scene but in holography, each piece shows the whole scene.

Notes:
Chief characteristics of an image formed in plane mirror are:

1. Image is erect and of equal size.
2. Image is virtual, it means the image cannot be taken on screen.
3. The distance of image from the mirror is same as the distance between object and mirror.
4. Image is laterally inverted. It means right hand side of the object appears as left hand side of the image and vice versa.

Notes:
The alpha particles have very large atomic volume and hence do not penetrate human skin.

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Uniform circular motion denotes the motion of an object in a circle at a constant speed. An object moves in a circle constantly changes its direction. Velocity and acceleration changes but the speed does not change.

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The first statement is not correct because the action of the air from the fan and reaction of the sail both would act on the boat itself.

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The speed of the sound increases when there is an increase in the temperature as well as moisture. Speed of the sound increases by 0.61 meter per second for each ° increase in temperature.

Notes:
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.

Notes:
The first statement need knowledge and second statement needs some commonsense. Beautiful rainbows, which sometimes arch across the sky during rain showers, do not appear during snow showers. This is because a snowflake has a different shape than a raindrop. When raindrops fall from the sky, they are round like tiny balls. To form a rainbow, the sun must shine on the raindrops. When a ray of sunlight reaches a raindrop, some of the light enters the drop and refracts. This means that the ray bends at the surface of the drop and changes its direction. Different colors of light refract in slightly different directions. This is how the white sunlight, which is really a combination of red, orange, yellow, green, blue and violet light, gets separated into different colors. Then each colored ray of light takes its own path inside the raindrop and exits in a different direction.
Therefore, when you look up at the rain in the sky, each color of light comes at you from a different direction, and you see a rainbow. In contrast to the simple round shape of raindrops, snowflakes are six-sided and flat. When sunlight shines on snowflakes tumbling and falling through the air, the many different surfaces of the snowflakes cause the light to be refracted and reflected in many different directions, and the light is too scattered to form a rainbow. However, in special situations snowflakes can create interesting and beautiful displays with sunlight. Parahelia, sometimes called “mock suns” or “sun dogs,” are bright spots that appear to the left and right of the sun. They form when rays of sunlight refract through thin plate-like snowflakes that are falling flat through calm air. Often each bright spot has a reddish side and a bluish side.
The rainbow is not located at a specific distance, but comes from any water droplets viewed from a certain angle relative to the Sun’s rays. Thus, a rainbow is not a physical object, and cannot be physically approached. Indeed, it is impossible for an observer to manoeuvre to see any rainbow from water droplets at any angle other than the customary one of 42 degrees from the direction opposite the Sun. Even if an observer sees another observer who seems “under” or “at the end” of a rainbow, the second observer will see a different rainbow further off-yet, at the same angle as seen by the first observer.

Notes:
Sidereal day is the time taken by the earth to complete one rotation about its axis w.r.t a fixed star Solar day is the time taken by the earth to complete one rotation about its axis w.r.t the sun. Shake is the smallest practical unit of time 1 shake = 10^-8s Tropical year: The year in which there is a total solar eclipse.

Notes:
The unit of Inductive Reactance is ‘ohm’. Inductive Reactance = Angular frequency x Inductance Inductive reactance is defined as the opposition to a changing current flow. It is measured in ohm. Any changing current in an inductor will be impeded because of the inductance associated with it.