# Physics GK Quiz-31

## Physics GK Quiz-31

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

### 601. A small drop of oil spreads over water because :

(1) oil has a higher surface tension
(2) water has a higher surface tension
(3) oil has a higher viscosity
(4) water has a higher viscosity
601. (2) Surface tension of oil is smaller than that of water. When oil is dropped on the surface of water, the force stretches the oil drops on all sides. Hence the oil spreads over the surface of water.

### 602. Which one among the following doesn't have any effect on velocity of sound ?

(1) Pressure
(2) Temperature
(3) Humidity
(4) Density
602. (3) The speed of sound varies depending on the temperature, pressure, and density of the medium through which the sound waves travel. In most of the cases, it is density which matters. Sound travels faster through denser air (or other material). The density of air is affected by atmospheric pressure, temperature, and altitude.

### 603. The motion of a body around a circular path is an example of

(1) Uniform velocity, variable acceleration
(2) Uniform speed, uniform velocity
(3) Uniform speed, variable velocity
(4) Uniform speed, variable acceleration
603. (1) Uniform circular motion occurs when a body moves in a circular path with constant velocity. The acceleration of a body experiencing uniform circular motion is always directed toward the center of the circle (centripetal acceleration or ac = 2v r where v is the body’s velocity, and r is the radius of the circle. This acceleration is constant in magnitude but changes in direction, so, it is variable at every
point of the circular path.

### 604. A current carrying conductor is associated with

(1) a magnetic field
(2) an electric field
(3) an electro-magnetic field
(4) an electrostatic field
604. (3) A current carrying conductor, such as a metal wire, will produce a magnetic field around it because of the motion of charge within the wire itself. This motion produces or sets up a magnetic field around the wire in the form of concentric circles. This electromagnetic effect is described in physics by the Biot-Savart Law, an experimentally deduced inverse-square law. The effect is also described by Ampere’s Law, which is derived from the Biot-Savart Law.

### 605. Green house effect is the heating up of the Earth’s atmosphere which is due to

(1) the ultraviolet rays
(2) g-rays
(3) the infra-red rays
(4) X-rays
605. (3) The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through a transparent medium and are absorbed, but the longer wavelengths of the infrared re-radiation from the heated objects are unable to pass through that medium. The trapping of the long wavelength radiation leads to more heating and a higher resultant temperature.

### 606. If the phase difference between two points is 120° for a wave with velocity of 360 m/ and frequency 500 Hz, then path difference between the two points is

(1) 1 cm
(2) 6 cm
(3) 12 cm
(4) 24 cm
606. (4) If v is the wave velocity and f is the frequency, wavelength (?) is given by: l = v f So as per the question, l = 360/500 = 0.72 The path difference between two points is given by l p f 2 ´ = 0 72 360 . 120 ° ´ ° = 0.24m = 24m

### 607. Clouds float in the atmosphere because of their

(1) low pressure
(2) low density
(3) low viscosity
(4) low temperature
607. (2) The key to why clouds float is that the density of the same volume of cloud material is less than the density of the same amount of dry air. Just as oil floats on water because it is less dense, clouds float on air because the moist air in clouds is less dense than dry air.

### 608. The threshold frequency is the frequency below which :

(1) photo current increases with voltage
(2) photo current decreases with voltage
(3) photo electric emission is not possible
(4) photo current is constant
608. (3) The photoelectric effect is the emission of electrons by substances, especially metals, when light falls on their surfaces. The photoelectric effect will not occur when the frequency of the incident light is less than the threshold frequency as the electrons are unable to gain sufficient energy to overcome the electrostatic barrier of the work function of the metal.

### 609. Tesla is a unit of magnetic :

(1) flux
(2) induction
(3) moment
(4) field
609. (4) The tesla (symbol T) is the SI derived unit used to measure magnetic fields. Tesla can be measured in different ways; for example, one tesla is equal to one Weber per square meter. The tesla was first defined in 1960 by the General Conference on Weights and Measures (CGPM). It was named in honor of the physicist, electrical engineer, and inventor, Nikola Tesla.

### 610. The damage of the human body due to radiation (X-rays or grays etc,) is measured in :

(1) Rems
(2) Roentgen
(3) Curie
610. (1) In the case of damage to human body due to radiation, the most important factor is the amount of the dose - the amount of energy actually deposited in the body. The absorbed radiation dose, the amount of energy absorbed per gram of body tissue, is usually measured in units called rads. Another unit of radation is the rem, or roentgen equivalent in man. For practical purposes, 1 rad (absorbed dose) = 1 rem or 1000 mrem (dose equivalent) (Source: United States Nuclear Regulatory Commission).

### 611. Transition ions absorb light in :

(1) infrared region
(2) ultraviolet region
(3) microwave region
(4) visible region
611. (4) Transition metal ions have an incomplete set of 3d electrons. Changes in the energy of these electrons correspond to the energy of visible light. The absorption of visible light by these ions lend colour to gems.

### 612. Flywheel is an important part of a steam engine because it :

(1) accelerates the speed of the engine
(2) helps the engine in keeping the speed uniform
(3) decreases the moment of inertia
(4) gives strength to the engine
612. (2) A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia and thus resist changes in rotational speed, enabling the engine to run at a constant, uniform motion. In the Industrial Revolution, James Watt contributed to the development of the flywheel in the steam engine.

### 613. The freezing point of fresh water is _______.

(1) 4°C
(2) 3°C
(3) 5°C
(4) 0°C
613. (4) The freezing point of water is the temperature at which water changes phase from a liquid to a solid. Under normal conditions, ordinary water freezes at 0°C, or 32°F. The temperature may be lower if supercooling occurs or if there are impurities present in the water which could cause freezing point depression to occur.

### 614. The unit of noise pollution (level) is :

(1) decibel
(2) decimal
(3) ppm
(4) None of these
614. (1) Noise pollution refers to any unpleasant, damaging or irritating noise that has the potential to harm people, wildlife or the environment. The decibel (dB) is the main unit used to measure the intensity or loudness of sounds. A sound can also be measured by its pitch, which is the frequency of sound vibrations per second.

### 615. Relative humidity is expressed as

(1) Grams
(2) Kilograms
(3) Percentage
(4) Ratio
615. (3) Relative humidity is the amount of moisture in the air compared to what the air can “hold” at that temperature. It signifies the mass of water vapour present in the air expressed as a percentage of the mass that would be present in an equal volume of saturated air at the same temperature. So Relative humidity is normally expressed as a percentage.

### 616. A real gas can act as an ideal gas in

(1) high pressure and low temperature
(2) low pressure and high temperature
(3) high pressure and high temperature
(4) low pressure and low temperature
616. (2) Real gases approximate ideal gases when their pressure is relatively low, and their temperature reasonably high. A real gas deviates increasingly from ideality as it is compressed and cooled to near the point at which it will condense into a liquid. Compressing forces the molecules closer together so that intermolecular forces become stronger, and cooling reduces the kinetic energy of the molecules, so that they are more easily held by these forces.

### 617. According to special theory of relativity the mass of a particle

(1) increases with increase in velocity with respect to an observer.
(2) decreases with increase in velocity.
(3) decreases with decrease in velocity.
(4) is independent of its velocity.
617. (1) According to the Special Theory of Relativity, the mass of a moving object measures more as its velocity increases until, at the speed of light, it becomes infinite. This is because as an object gains speed, it gains more (kinetic) energy.

### 618. The motion of the wheels of a bullock-cart while moving on the road is an example of

(1) Oscillatory and rotatory motion
(2) Oscillatory and translatory motion
(3) Translatory and rotatory motion
(4) Translatory motion only
618. (3) There are four basic types of motion in mechanical systems: Rotary, Linear, Reciprocating and Oscillating motion. Rotatory motion is turning round in a circle, such as a wheel turning. While the wheel is moving, the mechanism transfers translational motion into rotary motion. As a matter of fact, translatory motion and rotatory motion occur at the same time.

### 619. Purity of a metal can be determined with the help of

(1) Pascal’s law
(2) Boyle’s law
(3) Archimedes principle
(4) Conservation of mass principle
619. (3) Purity of a metal can be determined with the help of Archimedes Principle which makes use of the densities and buoyancy of metals. Finding the density of a metal sample can help to determine its purity. It is most commonly used in the checking the purity of gold.

(1) 2 times
(2) 4 times
(3) 8 times
(4) 16 times