Physics GK Quiz-19

Physics GK Quiz-19

Physics Multiple Choice Questions (MCQs) Quiz for State and UPSC Civil Services Examinations. Objective Questions on Physics for competitive examinations.

    361. Rise of oil a wick is due to

    (1) density of the oil
    (2) viscosity of the oil
    (3) surface tension of the oil
    (4) pressure of the oil
    Answer:
    361. (3) The phenomenon of rise or fall of liquid in a capillary tube is called capillarity. Oil rises through a wick due to capillarity. The narrow pores in the threads of a wick act like tiny capillaries, through which oil rises. Capillary action is the result of adhesion and surface tension.

    362. The radiation initially produced in fluorescent tube is

    (1) infrared
    (2) ultraviolet
    (3) microwaves
    (4) X-rays
    Answer:
    362. (2) The primary radiation that is initially produced within a fluorescent lamp is analogous to that emitted by a low pressure mercury lamp. Fluorescent lamps produce UV radiation by ionizing low-pressure mercury vapour. A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.


    363. The ‘four stroke petrol engine’ is based on

    (1) Carnot-cycle
    (2) Otto-cycle
    (3) Diesel-cycle
    (4) Boyle’s-cycle
    Answer:
    363. (2) A four-stroke engine (also known as four-cycle) is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two
    separate revolutions of the engine’s crankshaft, and one single thermodynamic cycle. The earliest of these to be developed is the Otto cycle engine developed in 1876 by Nikolaus August Otto in Cologne, Germany, after the operation principle described by Alphonse Beau de Rochas in 1861.

    364. It is dangerous to observe Solar eclipse with naked eyes because

    (1) Infrared radiations from sun burn our retina
    (2) Ultraviolet radiations from Sun burn our retina
    (3) All radiations from sun initiate chemical reactions in eyes
    (4) Cosmic rays reach eyes more during the eclipse
    Answer:
    364. (2) The solar radiation that reaches the surface of Earth ranges from ultraviolet (UV) radiation at
    wavelengths longer than 290 nm to radio waves in the meter range. The tissues in the eye transmit a
    substantial part of the radiation between 380 and 1400 nm to the light-sensitive retina at the back of
    the eye. The concern over improper viewing of the Sun during an eclipse is for the development of “eclipse blindness” or retinal burns.

    365. These waves cannot be transmitted through vacuum

    (1) Light
    (2) Sound
    (3) Heat
    (4) Electromagnetic
    Answer:
    365. (2) Sound is a mechanical wave that is created by vibrating objects and propagated through a medium from one location to another. Because mechanical waves rely on particle interaction in order to transport their energy, they cannot travel through regions of space that are void of particles. That is, mechanical waves cannot travel through a vacuum.

    366. A gap is left between two rails of a railway track to accommodate...... of the metal.

    (1) areal expansion
    (2) volume expansion
    (3) liner expansion
    (4) apparent expansion
    Answer:
    366. (3) The volume of materials changes depending on current temperature. Usually heat makes them
    expand, and cold leads them to contract. To a first approximation, the change in length measurements
    of an object (“linear dimension” as opposed to, e.g., volumetric dimension) due to thermal expansion is
    related to temperature change by a “linear expansion coefficient”. It is the fractional change in length per degree of temperature change.

    367. If an ordinary glass tube and a glass capillary tube are both dipped in a beaker of water, water rises in

    (1) both
    (2) only the glass tube
    (3) only the capillary tube
    (4) neither
    Answer:
    367. (1) The rise or fall of liquid due to capillarity in a beaker of water depends upon the radius of the bore of the tube (s) which is/are dipped into it. The narrower the bore of the tube, the greater is the rise or fall of the liquid in the tube. So in this case, water will rise in both the glass tube and the glass capillary tube.

    368. ‘Hydraulic brakes’ work on the principle of

    (1) Pascal’s law
    (2) Thomson’s law
    (3) Newton’s law
    (4) Bernoulli’s theorem
    Answer:
    368. (1) Pascal’s law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container. According to Pascal’s principle, in a hydraulic system a pressure exerted on a piston produces an equal increase in pressure on another piston in the system. If the second piston has an area 10 times that of the first, the force on the second piston is 10 times greater, though the pressure is the same as that on the first piston. This effect is exemplified by the hydraulic press, based on Pascal’s principle, which is used in such applications as hydraulic brakes.

    369. Stars in the sky appear to twinkle due to

    (1) a series of refractions
    (2) a series of reflections
    (3) a surface tension phenomenon
    (4) multiple diminishing brightness
    Answer:
    369. (1) The movement of air (sometimes called turbulence) in the atmosphere of Earth causes a series of refractions which makes the starlight to get slightly bent as it travels from the distant star through the
    atmosphere down to us on the ground. This means that some of the light reaches us directly and some
    gets bent slightly away. To our eyes, this makes the star seem to twinkle.

    370. A pilot has to release the bomb to hit a target

    (1) right above the target
    (2) beyond the target
    (3) before the target
    (4) None of these
    Answer:
    370. (3) According to Newton’s first law, an object that is at rest will stay at rest unless an unbalanced force acts upon it and an object that is in motion will not change its velocity unless an unbalanced force acts upon it. So the bomb carries the inertia of the aircraft and so has to be launched before the target so that it can hit it on time. Assuming the plane continues to fly straight forward, the plane will be directly over the target when the bomb hits.

    371. Parabolic mirros are used in

    (1) Car headlights
    (2) Driving mirrors
    (3) Dentists mirros
    (4) Shaving mirros
    Answer:
    371. (1) A parabolic reflector (mirror) transforms an incoming plane wave traveling along the axis into a spherical wave converging toward the focus. Since the principles of reflection are reversible, parabolic reflectors can also be used to project energy of a source at its focus outward in a parallel beam, used in devices such as spotlights and car headlights.

    372. Red is used as an emergency or danger signal as

    (1) it is a striking colour
    (2) its wavelength is the longest
    (3) it is scattered
    (4) it has very high energy
    Answer:
    372. (2) The effect of scattering is inversely related to the fourth power of the wavelength of a colour. Red has the highest wavelength of all the colours and is able to travel the longest distance through fog, rain, and the alike.

    373. Bats can sense obstacles because they produce

    (1) supersonic sound waves
    (2) ultrasonic sound waves
    (3) infrasonic sound waves
    (4) micro sound waves
    Answer:
    373. (2) The reason that bats use ultrasound is because it has such a high frequency and it has a low diffraction or it bends less. They use this sound to do a couple of things like to catch their prey and also just to get around. The method of doing such tasks is called echolocation. They make a sound and wait for it to bounce back to hear it. If they hear it come faster in a particular area than the rest of the sounds then they know that something is near.

    374. The resistance of the human body (dry condition) is of the order of

    (1) 101 Ohm 
    (2) 102 Ohm
    (3) 103 Ohm 
    (4) 104 Ohm
    Answer:
    374. (*) The level of current passing through the human body is directly related to the resistance of its path through the body. Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body’s resistance to 1,000 Ohms. (Source: The Guide to Photovoltaic System Installation by Gregory Fletcher)

    375. The sharpness of a television image is termed as its

    (1) Clarity 
    (2) Colour
    (3) Resolution
    (4) Graphics
    Answer:
    375. (3) Resolution is an umbrella term that describes the detail an image holds. The term applies to raster digital images, film images, and other types of images. The display resolution of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed.

    376. Small bubbles are perfectly spherical because of

    (1) Gravity
    (2) Pressure
    (3) Viscosity
    (4) Surface tension
    Answer:
    376. (4) Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer. In the absence of other forces, including gravity, drops of virtually all liquids would be perfectly spherical. The spherical shape minimizes the necessary “wall tension” of the surface layer according to Laplace’s law.

    377. The final image in a simple microscope is

    (1) real, diminished and inverted
    (2) real, magnified and erect
    (3) virtual, magnified and erect
    (4) virtual, diminished and erect
    Answer:
    377. (3) A basic microscope is made up of two converging lenses. The first lens creates a real image which serves as the object for the second lens, and the image created by the second lens is the one a viewer sees. The final image is magnified, virtual and is inverted compared to the original object.

    378. Two rods, one of copper and other of steel, experience the same upthrust when placed in water.Thus, both have

    (1) equal volume
    (2) equal weight
    (3) equal density
    (4) equal mass
    Answer:
    378. (1) When a body is placed in water, the upthrust or buoyant force acting on it depends upon the following factors: (i) Volume of the body submerged in the liquid - (V), or volume of the liquid displaced - (V); (ii) Density of the liquid - (d); and (iii) Acceleration due to gravity In-line. Since in the present question, we can assume g to be a constant and know that steel and copper have different densities, the only case in which they can have similar upthrust will be because of their volumes.

    379. A single fixed pulley is used to draw water from a well because

    (1) efficiency is 100%
    (2) velocity ratio is low
    (3) mechanical advantage is high
    (4) force is applied in a convenient direction
    Answer:
    379. (4) A single fixed pulley is used to lift a load upwards by applying efforts downwards. The load and effort move equal distance but in opposite directions. This is convenient as to apply effort in downward direction. They are used on flag-poles and to draw water from a well.

    380. A light year is a measure of :

    (1) Speed 
    (2) Velocity
    (3) Distance 
    (4) Time
    Answer:
    380. (3) A light-year is a unit of length equal to just under 10 trillion kilometres (or about 6 trillion miles). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in a vacuum in one Julian year. Note that the light-year is a measure of distance (rather than, as is sometimes misunderstood, a measure of time).

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