Physics GK Quiz-35

Physics GK Quiz-35

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

    681. Which of the following options correctly explains the term heat budget?

    (1) It is a mode of transfer of heat through matter by molecular activity.
    (2) It is the balance between incoming and outgoing radiation
    (3) It is the radiation from the earth in the form of long waves.
    (4) It is the amount of heat which the surface of earth receives from the sun.
    Answer:
    681. (2) Incoming heat being absorbed by the Earth, and outgoing heat escaping the Earth in the form of radiation are both perfectly balanced. If they were not balanced, then Earth would be getting either progressively warmer or progressively cooler with each passing year. This balance between incoming and outgoing heat is known as Earth’s heat budget.

    682. The purpose of choke in a fluorescent lamp is :

    (1) to increase the current flow
    (2) to decrease the current flow
    (3) to decrease the resistance
    (4) ro decrease the voltage momentarily
    Answer:
    682. (2) The choke primarily serves to limit current flow to the correct level for the tube. It also can be used during startup to provide an inductive ‘kick’ forming a momentary higher-voltage pulse to start the lamp.

    683. The mercury and sodium street lamps light up because of :

    (1) Atomic emission
    (2) Atomic absorption
    (3) Electron emission
    (4) Electron absorption
    Answer:
    683. (1) The light in sodium vapour lamp and mercury vapour lamp is, because of electron emission. In case of Sodium Lamps, filaments of the lamp sputter fast moving electrons, which hit the sodium atoms (vapour) causing the valence electrons of the sodium atoms to excite to higher energy levels and the electrons thus excited relax by emitting the characteristic monochromatic bright yellow light. The mechanism in mercury vapour lamp is more involved and sequential. The sputtered electrons from the filaments, after having been accelerated by high voltage, hit the mercury atoms. Here also, the excited electrons of mercury atoms relax by emitting characteristic but ultraviolet light.

    684. A person can jump higher on the moon’s surface than on the earth because :

    (1) the moon’s surface is rough
    (2) the acceleration due to gravity in moon is smaller than that on the earth.
    (3) the moon is cooler than earth
    (4) the moon has no atmosphere
    Answer:
    684. (2) The acceleration due to the gravitational field of moon (g’ = 1.62631 ms-2) is one-sixth of the acceleration due to gravity on the Earth. So the weight of the same body is also 1/6th on moon in comparison to that on the surface of the earth. It is due to this reason; a man can jump six times higher on moon than on earth.

    685. Which of the following colour of light deviates least through the prism?

    (1) yellow 
    (2) green
    (3) violet 
    (4) red
    Answer:
    685. (4) In refracting media like glass prism, water, etc., lights of different colors travel with different speeds. The speed of violet colour is the least, while the speed of red colour is the largest in prism. As a result, the refractive index of glass is largest for violet colour and least for red colour. So the violet colour is deviated the most, while red colour is deviated least on passing through the prism.

    686. Hydraulic brakes work on the principle of

    (1) Thomson’s law
    (2) Newton’s law
    (3) Bernoulli’s theorem
    (4) Pascal’s law
    Answer:
    686. (4) Hydraulic brake works on Pascal’s law which states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations remain the same. The wheel cylinder of hydraulic drum brakes acts as a double hydraulic press, multiplying the force on the fluid by the ratio of the area of the cylinder to the area of the supply line. Besides the muliplication of force achieved, Pascal’s principle guarantees that the pressure is transmitted equally to all parts of the enclosed fluid system.

    687. Which one of the following is not a feature of Indifference Curve?

    (1) They do not intersect each other
    (2) They slope downwards to the right
    (3) They are parallel to each other
    (4) They are concave to each other
    Answer:
    687. (4) Indifference curves are usually convex to the origin. In other words, the indifference curve is relatively flatter in its right-hand portion and relatively steeper in its left-hand portion. The degree of convexity of an indifference curve depends on the rate of fall in the marginal rate of substitution.

    688. The apparent weight of a man in a lift is less the real weight when :

    (1) the lift is going up with an acceleration
    (2) the lift is going down with uniform speed
    (3) the lift is going up with uniform speed
    (4) the lift is going down with an acceleration
    Answer:
    688. (4) If the lift accelerates downwards with acceleration a, then the apparent weight of the man standing in the lift will be less than the true weight of the man by an amount ma. On the contrary, if the lift accelerates upwards with acceleration, then the apparent weight of the man will be greater than his true weight.


    689. Rainbows are produced when sunlight :

    (1) Incident on rain drops hanging in the atmosphere is dispersed after suffering refraction
    (2) Incident on rain drops hanging in the atmosphere is dispersed after suffering refraction and internal reflection.
    (3) Incident on raindrops hanging in the atmosphere is dispresed after suffering reflection.
    (4) None of the given statements is correct.
    Answer:
    689. (2) When the light rays from the Sun are incident on water drops hanging in the atmosphere; these rays are dispersed into seven colours of white light and internally reflected by the drops. This dispersion and internal reflection results in production of colour arcs which appear hanging in the sky and known as rainbow. So the solar rays incident on the rain drops are refracted, internally reflected and transmitted to form the rainbow.

    690. Sound is heard over longer distances on rainy days because

    (1) sound travels slowly in moist air
    (2) sound travels faster in moist air
    (3) moist air does not absorb sound
    (4) moist air absorbs sound
    Answer:
    690. (2) The speed of sound in a medium is inversely proportional to the square root of its density. Higher is the humidity in the air, greater will be the velocity of sound. Therefore, the speed of sound in moist air is more than that in dry air. This is why the sirens of mills, whistle of trains and others are heard up to longer distances on a rainy day than on a dry day.

    691. X–rays are

    (1) positively charged particles
    (2) negatively charged particles
    (3) neutral particles
    (4) None of these
    Answer:
    691. (3) Like gamma rays and neutrons, X-rays are electrically neutral. They have neither a positive nor a negative charge. They cannot be accelerated or made to change direction by a magnet or electrical field. In contrast, charged subatomic particles comprise light charged particles (electrons and positrons) and heavy charged particles (protons, alpha particles and heavier ions).

    692. Railway tracks are banked on curves so that :

    (1) the train may not fall down inwards.
    (2) the weight of the train may be reduced.
    (3) necessary centripetal force may be obtained from the horizontal component of the normal reaction due to track.
    (4) no frictional force may be produced between the wheels and the track.
    Answer:
    692. (3) A vehicle moving at a fast speed on a straight rail/ road has a large inertia, i.e. tendency to keep moving in the same direction at the same speed. When it takes a circular turn on a curved rail/road, it experiences an additional force, termed as centripetal force, acting towards the centre of the circle. While rounding the curve as the vehicle has tendency to leave curved path and regain straight line path, force of friction between wheels and ground provides necessary centripetal force. In order that the vehicle can go round the curved track at a reasonable speed without skidding, the sufficient centripetal force is managed for it by banking the rail/road.


    693. We feel cool when we sit near the fan, this is because

    (1) fan gives cool air.
    (2) fan cools surrounding air.
    (3) air vapourises the sweat on our body.
    (4) we feel cool when air touches the body.
    Answer:
    693. (3) We feel comfortable sitting under a fan when we are perspiring because a fan increases the rate of evaporation of sweat (or moisture) from our body and makes us feel cool and comfortable.

    694. The average kinetic energy of the molecules of an ideal gas is directly proportional to

    (1) Velocity of Molecules
    (2) Mass of Molecules
    (3) Absolute temperature of the gas
    (4) Temperature of environment
    Answer:
    694. (3) The average kinetic energy of gas molecules is directly proportional to absolute temperature only. This implies that all molecular motion ceases if the temperature is reduced to absolute zero.

    695. Which one of the following is a non-dimensional quantity?

    (1) Gas constant
    (2) Strain
    (3) Co-efficient of viscocity
    (4) Plank’s constant
    Answer:
    695. (2) A dimensionless quantity is simply a quantity that has no units and therefore no dimensions. A ratio between two numbers is a non-dimensional or dimensionless quantity. Strain which is defined as change in dimension over original dimension has no dimensional formula. So it is a dimensionless quantity.

    696. When water freezes its density

    (1) Decreases
    (2) Becomes Zero
    (3) Remains constant
    (4) Increases
    Answer:
    696. (1) Water at ordinary temperatures contracts and increases in density as it is cooled, like most substances. But at about 4°C it reaches a maximum density and then decreases in density as it approaches the freezing point. This is referred to as anomalous property of water.

    697. Which of the following property of sound is affected by change in air temperature

    (1) Frequency 
    (2) Intensity
    (3) Amplitude 
    (4) Wavelength
    Answer:
    697. (4) The wavelength of sound changes with temperature. This is because the speed of sound changes with the temperature. Since the speed of sound is different at different temperature, this means the wavelength of sound at a given frequency is a variable depending on the speed of sound. For example, the wavelength of a 100 cycle tone in air at 68ºF would be 11.27 feet while the same tone in fresh water at 68ºF would have a wavelength of 48.05 feet.

    698. A bullet of mass ‘m’ and velocity ‘a’ is fired in to a large block of wood of mass ‘M’. The final velocity of the system is

    (1) Mm M +a 
    (2) mm M +a
    (3) m M+ ma 
    (4) m M+ Ma
    Answer:
    698. (2) If v is the final velocity, then according to the principle of conservation of momentum, m
    1v1 + m2v2 = (m1+m2)v; or, v = m1v1 + m2v2/(m1+m2) Using values from the question, v = m a + 0/ (m + M) = ma/ (m + M)

    699. The intensity ratio of waves is 25 : 9. What is the ratio of their amplitudes?

    (1) 50 : 18 
    (2) 25 : 9
    (3) 3 : 5 
    (4) 5 : 3
    Answer:
    699. (4) 

    700. When number of turns in a coil is trippled, without any change in the length of coil, its self inductance becomes?

    (1) Nine times 
    (2) Three times
    (3) Six times 
    (4) One–third
    Answer:
    700. (1) 

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