Physics GK Quiz-39

Physics GK Quiz-39

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

    761. During which of the following operating conditions of an automobile, carbon monoxide content in exhaust gas is maximum?

    (1) Acceleration
    (2) Cruising
    (3) Idle running
    (4) Deacceleration
    Answer:
    761. (3) High Carbon Monoxide (CO) content in exhaust gas of automobiles usually indicate a fuel mixture richer than ideal (rich mixture - air fuel ratio below 14.7).High CO levels result from inadequate O2 supply needed for complete combustion that is caused by a too rich mixture - too much fuel or not enough air. This is most seen during : l Idle running or low idle speed; l Improper float settings in carbureted vehicles; l Dirty or restricted air filters; l Excessively dirty or contaminated oil
    l Improper operation of the fuel delivery system; etc. 

    762. The least distance of distinct vision is

    (1) 35 cm 
    (2) 25 cm
    (3) 45 cm 
    (4) 15 cm
    Answer:
    762. (2) Least distance of distinct vision is the minimum object’s distance that is able to produce a distinct image on the retina.This distance is about 25 cm from the eye. However, it varies with age. For infants the least distance of distinct vision is about 5 to 8 cm.

    763. The component used for tuning a radio is basically a variable

    (1) Resistor 
    (2) Condenser
    (3) Inductor
    (4) Transformer
    Answer:
    763. (2) A tuning capacitor or tuning condenser is a variable capacitor used in an electronic circuit of a radio. It usually connects in parallel to a loop antenna and its capacitance may be intentionally and repeatedly changed mechanically or electronically.

    764. 0°K is equivalent to

    (1) 273°C 
    (2) – 273°C
    (3) 0°C 
    (4) 100°C
    Answer:
    764. (2) 0 degrees Kelvin is equal to -273.15 degrees Celsius. It is the lowest possible temperature, at which all molecules are have the least possible amount of kinetic energy. It refers to a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0.

    765. The term ‘Higgs Boson’ is associated with

    (1) Nano Technology
    (2) Oncology
    (3) God Particle
    (4) Stem Cell Research
    Answer:
    765. (3) The Higgs boson is an elementary particle in the Standard Model of particle physics. That is often referred to as the “God particle” in popular media outside the scientific community. The nickname comes from the title of the 1993 book on the Higgs boson and particle physics, The God Particle: If the Universe Is the Answer, What Is the Question? by Nobel Physics prizewinner Leon Lederman.

    766. Addition of suitable impurities into semiconductor, is called

    (1) Doping 
    (2) Mixing
    (3) Forming 
    (4) Diluting
    Answer:
    766. (1) In semiconductor production, doping refers to the introduction of impurities into an extremely pure intrinsic semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor and the properties that it needs to have for its intended purpose.

    767. At low temperature, Lead behaves as a :

    (1) Semi conductor
    (2) Super conductor
    (3) Insulator
    (4) Conductor
    Answer:
    767. (2) Lead exhibit superconducting phase transitions at low temperatures of 7.2 Kelvin. This discovery was made in 1913. At this temperature (known as critical temperature), the electrical resistivity of lead drops to zero. The transition is so sudden and complete that it appears to be a transition to a different phase of matter; this superconducting phase is described by the BCS theory.

    768. The absolute zero is a temperature at which _______

    (1) molecular motion in a gas would cease
    (2) water freezes
    (3) all gases become liquid
    (4) all gases become solid
    Answer:
    768. (1) Absolute zero is the lowest possible temperature where nothing could be colder and no heat energy remains in a substance. It is the point at which all motion in matter stops. By international agreement, absolute zero is defined as precisely; 0 K on the Kelvin scale, which is a thermodynamic (absolute) temperature scale; and –273.15 degrees Celsius on the Celsius scale.

    769. Intensity of any wave is proportional to which of the following?

    (1) Amplitude
    (2) Square of amplitude
    (3) Square root of amplitude
    (4) Cube of amplitude
    Answer:
    769. (2) The energy of a wave is proportional to the square of its amplitude. Therefore, the intensity of a wave is also proportional to the square of its amplitude. This means that if Intensity drops off at a rate of 1/r2, wave amplitude drops off at a rate of 1/r.

    770. The large collection of stars, dust and gas held together by gravitational attraction between components is known as

    (1) Cluster
    (2) Atmosphere
    (3) Galaxy
    (4) Sun Family
    Answer:
    770. (3) The term galaxy refers to a large collection of stars, dust, and gas clouds which are held together by gravitational attraction.The smallest galaxies may contain only a few hundred thousand stars, while the largest galaxies have thousands of billions of stars. The Milky Way galaxy contains our solar system.

    771. Purpose of an optical filter is to

    (1) reflect lights of different colours
    (2) dispense light into component colours
    (3) refract light of different colours
    (4) transmit or absorb light of different colours
    Answer:
    771. (4) Optical filters are devices that selectively transmit light in a particular range of wavelengths, that is, colors, while blocking the remainder. They are commonly used in photography (where some special effect filters are occasionally used as well as absorptive filters), fluorescence microscopy, spectroscopy, clinical chemistry, colour stage lighting, etc.

    772. In the absence of the earth’s atmosphere, sky would appear

    (1) blue 
    (2) deep red
    (3) white 
    (4) black
    Answer:
    772. (4) Sky appears blue because the tiny particles of the earth’s atmosphere scatter the blue colour (short wavelength) of the sunlight more dominantly than other wavelengths. A blue sky is a manifestation of Rayleigh scatter. The sky would appear black in the absence of earth’s atmosphere because there would be no particles to scatter the light.

    773. If electric resistance is to be decreased, then the number of resistances should be connected in _______

    (1) Series 
    (2) Parallel
    (3) Mixed arrangement
    (4) None of these
    Answer:
    773. (2) Resistors are in parallel when each resistor is connected directly to the voltage source by connecting wires having negligible resistance. Each resistor thus has the full voltage of the source applied to it.When resistors are connected in parallel, more current flows from the source than would flow for any of them individually, so the total resistance is lower. Each resistor in parallel has the same full voltage of the source applied to it, but divide the total current amongst them.

    774. The material used in electric heater is

    (1) Tungsten 
    (2) Nichrome
    (3) Brass 
    (4) Steel
    Answer:
    774. (2) Due to its resistance to oxidation and stability at high temperatures, Nichrome is widely used in electric heating elements, such as in appliances and tools. Typically, nichrome is wound in coils to a certain electrical resistance, and current is passed through it to produce heat.

    775. Which one of the following processes is responsible for the glittering of air bubble rising through water?

    (1) Reflection of light
    (2) Refraction of light
    (3) Total internal reflection of light
    (4) Scattering of light
    Answer:
    775. (3) Total internal reflection is responsible for glittering which occurs when the light from a denser media (liquid) tries to enter less dense media (air in bubble). This reflected light when captured by our eyes is seen as glittering.

    776. In an optical fibre the signal is transmitted

    (1) in a straight line path
    (2) In a curved path
    (3) due to total internal reflection
    (4) Due to refraction
    Answer:
    776. (3) Total internal reflection is the basic concept behind the optical fiber. Optical fiber employs the transmission of light down fibers of plastic or glass. Because the fibers are thin, light entering one is likely to strike the inside surface at an angle greater than the critical angle and, thus, be totally reflected. In fact, most fibers have a varying refractive index to allow more light to be guided along the fiber through total internal refraction.

    777. What type of lens is used to correct vision of a person suffering from Myopia?

    (1) Convex lens
    (2) Concave lens
    (3) Crossed lens
    (4) Cylindrical lens
    Answer:
    777. (2) Near-sightedness, also known as short-sightedness and myopia, is a condition of the eye where light focuses in front of, instead of on, the retina. This causes distant objects to be blurry while close objects appear normal. This defect can be corrected by wearing a concave (diverging) spectacle lens. The rays of light from a near object are diverged before entering the eye so that the cornea and eye lens can direct the focal point onto the retina.

    778. A man standing close to the platform at a railway station experiences a pulling force towards a fast moving train because of __________ .

    (1) gravitational force between train and man
    (2) illusion of the man
    (3) the centripetal force
    (4) pressure difference due to fast moving air in between
    Answer:
    778. (4) When a fast-moving train passes a man standing on the platform at rest, the air between train and person also moves with greater speed. This rapidly moving air, by Bernoulli’s principle will have a lower pressure than the still air a few feet away. The still air, having higher pressure, and being behind the man standing close will tend to push him toward the train.

    779. Water is used in a hot water bag because

    (1) It is easily available
    (2) It has high specific gravity
    (3) It has high specific heat
    (4) It is a liquid substance
    Answer:
    779. (3) Water has the highest specific heat of any known substance except hydrogen; that is, it requires more heat to raise the temperature of water a definite number of degrees than it does to raise the temperature of an equal amount of any other substance the same number of degrees. Practically this same thing can be stated in another way: Water in cooling gives out more heat than any other substance in cooling through the same number of degrees. For this reason water is used in foot warmers and in hot-water bags (General Science by Bertha Clark).

    780. The temperature of a liquid is 32° F. What is its temperature in Celsius scale?

    (1) 32° C 
    (2) 0° C
    (3) 100° C 
    (4) 212° C
    Answer:
    780. (2) The formulas for converting between degree Celsius and degree Fahrenheit are: °F = °C 9/5 + 32 and °C = (°F - 32) 5/9. So in Celsius scale, 32o F= 0o C

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