Physics GK Quiz-42

Physics GK Quiz-42

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

    821. Which of the following waves cannot be polarised?

    (1) Radio 
    (2) Ultra violet
    (3) Infrared 
    (4) Ultrasonic
    Answer:
    821. (4) Only transverse waves (such as radio, ultraviolet and infrared waves) can be polarized since their vibrations can potentially occur in all directions perpendicular to the direction of travel. It is therefore possible to confine the vibrations to a single plane. However, sound waves are longitudinal in which vibrations are parallel to the direction of travel of the wave. The vibrations of a longitudinal wave occur along a single line, it is therefore not possible to confine that to a plane. So it cannot be polarized.

    822. Absolute Zero is defined as

    (1) The temperature at which all molecular motion ceases
    (2) At which water boils at 298K
    (3) At which liquid Helium boils
    (4) At which the volume becomes zero
    Answer:
    822. (1) Absolute zero is the temperature at which all motion in matter stops and is thought to be unreachable. It is the point at which the fundamental particles of nature have minimal vibrational motion, retaining only quantum mechanical, zero-point energyinduced particle motion. 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.

    823. Electromagnet is constructed with which of the following ?

    (1) Steel 
    (2) Soft Iron
    (3) Aluminium 
    (4) Nickel
    Answer:
    823. (2) An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off. It is made of soft iron since it has the property of losing its magnetism very quickly. The soft iron core of the electromagnet makes the magnetic field stronger.

    824. A body moving in a circular path with a constant speed has a

    (1) constant velocity
    (2) constant acceleration
    (3) constant kinetic energy
    (4) constant displacement
    Answer:
    824. (3) In circular motion, the magnitude of the velocity of the body is constant but the direction is constantly changing. This means that, even though the speed is not changing, the velocity is changing. This means that body moving in a circular is accelerating. At any instant, the direction of the velocity is a tangent to the circular path. A body moving at constant speed in a circular path experiences an acceleration directed towards the centre of the circular path. This acceleration is called a centripetal acceleration and is provided by a centripetal force. Overall, the displacement, velocity and acceleration are vector quantities. They change; but kinetic energy remains constant because the speed is constant.

    825. The Solar energy produced by

    (1) Fusion reaction
    (2) Fission reaction
    (3) Combustion reaction
    (4) None
    Answer:
    825. (1) The Sun is a main-sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. In its core, the Sun fuses 620 million metric tons of hydrogen each second. Fusion is a nuclear reaction in which two or more atomic nuclei come very close and then collide at a very high speed and join to form a new nucleus.

    826. On a cold day when the room temperature is 15°C, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15°C, because :

    (1) metals have higher thermal capacity than plastics
    (2) plastics have a lower density than metals
    (3) metals are good conductors of heat
    (4) plastics have a higher thermal conductivity than metals
    Answer:
    826. (3) On a chilly day, the room temperature is lower than our body temperature. Since metals have a higher coefficient of thermal conductivity than plastic, they are better conductor of heat than plastic. So, when we touch the metal cap and the plastic body of a pen, heat from our fingers will flow to the metal cap much more quickly than to the plastic body.

    827. Copper wires are generally used for electrical power transmission instead of iron wire because :

    (1) copper is cheaper than iron
    (2) copper is lighter than iron
    (3) copper is a better conductor of electricity than iron
    (4) copper can take higher power than iron
    Answer:
    827. (3) Copper is generally preferred for electrical power transmission instead of iron because of its high electrical conductivity and low resistivity. The conductivity (in s (S/m) at 20 °C) of copper is 5.96×107, while that of iron is 1.00×107. Among metals, silver has the highest electrical conductivity of 6.30×107, but it is not used commonly due to its high cost.

    828. Transformer is a device to convert

    (1) D.C. to A.C.
    (2) Low voltage D.C. into high voltage D.C.
    (3) Low voltage A.C. into high voltage A.C.
    (4) Mechanical energy into Electrical energy
    Answer:
    828. (3) A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling with no moving parts. It converts high voltage AC into low voltage AC and vice-versa. It is based upon the principle of mutual induction. Transformers alone cannot convert AC to DC or DC to AC; besides, they cannot change the voltage or current of DC.

    829. Quality of a musical note depends on

    (1) Fundamental frequency
    (2) Amplitude of the wave
    (3) Harmonics present
    (4) Velocity of sound in the medium
    Answer:
    829. (3) Sound “quality” or “timbre” describes those characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness. Timbre is mainly determined by the harmonic content of a sound and the dynamic characteristics of the sound such as vibrato and the attack-decay envelope of the sound. Harmonic content is the most important of these.

    830. The reverse effect of X–ray emission is

    (1) Raman effect
    (2) Compton effect
    (3) Zeeman effect
    (4) Photoelectric
    Answer:
    830. (4) When fast moving electrons strike on high atomic weight substance, X – ray is produced. In contrast, Photoelectric effect takes place when radiation of sufficient frequency incident on the metal surface and electrons are emitted. Hence, X – ray is the inverse phenomenon of photoelectric effect.

    831. The group of solar cells joined together in a definite pattern is called a

    (1) Battery
    (2) Solar heater
    (3) Solar cooker
    (4) Solar cell panel
    Answer:
    831. (4) A single solar cell can produce only a small amount of electricity. In those cases where more electrical power is needed, a large number of solar cells are joined in series. This group of solar cells is called a ‘solar cell panel’. Thus, a solar cell panel consists of a large number of solar cells joined together in a definite pattern.

    832. One nanometer is equal to ______ meters.

    (1) 10 raised to the power (-3)
    (2) 10 raised to the power (-6)
    (3) 10 raised to the power (-9)
    (4) 10 raised to the power (-12)
    Answer:
    832. (3) A nanometer is a unit of spatial measurement that is 10-9 meter, or one billionth of a meter. It is often used to express dimensions on an atomic scale. It is commonly used in nanotechnology, the building of extremely small machines.

    833. What is the unit of relative density?

    (1) kg/m 
    (2) kg/m2
    (3) kg/m3
    (4) It has no unit
    Answer:
    833. (4) Relative density is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.So, it is a dimensionless quantity and has no unit.

    834. Acceleration is

    (1) Inversely proportional to force
    (2) Inversely proportional to mass
    (3) Directly proportional to mass
    (4) Directly proportional to force
    Answer:
    834. (1) Acceleration, in physics, is the rate of change of velocity of an object with respect to time. An object’s acceleration is the net result of any and all forces acting on the object, as described by Newton’s Second Law. Newton’s second law of motion states that acceleration is directly proportional to net force when mass is constant.

    835. Vegetables are cooked in lesser time by adding a pinch of salt while cooking because

    (1) boiling point of water increases
    (2) latent heat of vaporization of water decreases
    (3) latent heat of vaporization of water increases
    (4) boiling point of water decreases
    Answer:
    835. (1) Adding salt raises the boiling point of water, which allows food to cook at higher temperature. The higher the temperature, the higher the rate of heat transfer between the food and water, thus it cooks more quickly.

    836. Hydraulic brakes in automobile work on

    (1) Poiseuille’s principle
    (2) Pascal’s principle
    (3) Archimedes’ principle
    (4) Bernoulli’s principle
    Answer:
    836. (2) The hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing glycol ethers or diethylene glycol, to transfer pressure from the controlling mechanism to the braking mechanism. It works on the principle of Pascal’s law which states that “pressure at a point in a fluid is equal in all directions in space”. When pressure is applied on a fluid it travels equally in all directions so that uniform braking action is applied on all wheels.

    837. The fuse in an electric circuit is connected in

    (1) series with neutral
    (2) parallel to live
    (3) parallel to neutral
    (4) series with live
    Answer:
    837. (4) A fuse wire is a safety wire connected in series with the live wire that has high resistivity and low melting point. Fuses are always connected in series with the component(s) to be protected from overcurrent. In case of any large current supply or malfunctioning in the electric connections, it melts and breaks the electric circuit.

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