# Physics GK Quiz-25

## Physics GK Quiz-25

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

### 481. Ozone layer in the outer atmosphere helps us in

(2) regulating the temperature of atmosphere
(3) absorbing cosmic ray particles
481. (4) The ozone layer is a layer in Earth’s atmosphere containing relatively high concentrations of ozone (O3) which absorbs 97–99% of the Sun’s medium-frequency ultraviolet light.

### 482. Water is used in hot water bags because

(1) It is easily obtained
(2) It is cheaper and is not harmful
(3) It has high specific heat
(4) It is easy to heat water
482. (3) The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance. As a result, water plays a very important role in temperature regulation.

### 483. Water drops cannot stick to the oily surface due to

(2) surface tension
(3) cannot mix each other
(4) water is lighter than oil
483. (2) The separation of oil and water is caused due to the difference in surface tension of the two liquids. The water molecules stick together tightly and does not mix with the oil because water molecules are attracted to each other very strongly, forming an invisible “skin” of surface tension around each drop.

### 484. Which of the following properties is generally found in nonmetals?

(1) Brittleness
(2) Conductivity
(3) Ductility
(4) Malleability
484. (1) An important physical property of non metals is that they are brittle and hence cannot be beaten into sheets or drawn into wires. In other words, non-metals are non-malleable and non-ductile. Where stress is applied on non-metals, they shatter into pieces.

### 485. Match the following:

Process
a. Evaporation
b. Sublimation
c. Freezing
d. Melting
Changes
1. Liquid into gas
2. Gas into liquid
3. Solid into gas
4. Solid into liquid
a b c d
(1) 1 2 4 3
(2) 3 1 2 4
(3) 2 1 4 3
(4) 2 1 3 4
485. (*) Evaporation: the process by which water is converted from its liquid form to its vapor form (gas); Sublimation: the transition of a substance directly from the solid phase to the gas phase without passing through an intermediate liquid phase; Freezing: a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point; and Melting: the process of heating a solid substance to a liquid.

### 486. Electrostatic precipitator is used to control

(1) Chemical Pollutants
(3) Water Pollutants
(4) Air Pollutants
486. (4) An Electrostatic precipitator is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. They are useful in controlling air pollutants in particulate form. They are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.

### 487. A micron is equal to

(1) 0.1 mm
(2) 0.01 mm
(3) 0.001 mm
(4) 0.0001 mm
487. (3) 1 micron = 0.001 millimeters. A micrometre (micron) is one-millionth of a metre (or one-thousandth of a millimetre, 0.001 mm). Its unit symbol in the International System of Units (SI) is µm. It is a common unit of measurement for wavelengths of infrared radiation as well as sizes of cells and bacteria.

### 488.Persons suffering from myopia are advised to use

(1) convex lens
(2) concave lens
(3) plano-convex lens
(4) plano-concave lens
488. (2) A concave lens is used to correct short-sightedness (myopia). In myopia, images are formed in front of the retina, resulting in a blurred image. This occurs when the eye is relatively too long or the refractive powers of the cornea and lens of the eye are relatively too strong.

### 489. A light year is a unit of

(1) time
(2) distance
(3) speed of light
(4) intensity of light
489. (2) As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in a vacuum in one Julian year. It is a measure of distance (rather than, as is sometimes misunderstood, a measure of time).

### 490. An instrument that records earthquakes is

(1) Ergograph
(2) Ediograph
(3) Thermograph
(4) Seismograph
490. (4) Earthquakes generate seismic waves which can be detected with a sensitive instrument called a
seismograph. The earliest seismograph was invented in China A.D. 136 by a man named Choko.

### 491. Velocity of sound in air does not depend on

(1) Density of air
(2) Temperature of air
(3) Pressure of air
(4) Humidity of air
491. (3) Assuming air to be an ideal gas, the speed of sound depends on temperature only. As air temperature increases, so does the speed of sound and vice versa. The speed of sound is completely independent of air pressure because the air pressure and air density are proportional to each other at the same temperature. The speed of sound in air depends on the density of air which in turn depends on the
temperature. The speed of a sound wave in air depends upon the properties of the air, mostly the
temperature, and to a lesser degree, the humidity.

### 492. A dynamo is used to convert

(1) mechanical energy into electrical energy
(2) electrical energy into mechanical energy
(3) electrical energy into magnetic energy
(4) magnetic energy into mechanical energy
492. (1) A dynamo converts mechanical energy into electrical energy by taking advantage of a phenomenon known as electromagnetic induction. It is an electric generator that is similar to those that provide electricity to our homes.

### 493. Conversion of sound energy into electrical energy is done by

(1) Solar cell
(2) Gramophone
(3) Microphone
(4) Loudspeaker
493. (3) Conversion of sound energy into electrical energy is done by microphone.

### 494. A small gap is left at the joints of rails in a railway track to

(1) avoid the tracks being distorted due to seasonal temperature variation
(2) avoid the heating of tracks to high temperature
(3) control the speed of train
(4) keep the rails equidistant
494. (1) A small gap is left at the joints of rails in a railway track to provide space for the expansion of rail pieces when the temperature rises during summer.

### 495. Which of the following criterion is used for any metal to be used as a cooking material ?

(1) More specific heat
(2) More thermal conductivity
(3) Less thermal conductivity
(4) Less electrical conductivity
495. (3) A metal to be used as a cooking material should have less thermal conductivity.

### 496. Least audible sound for most of the human ear is :

(1) 10.0 µ bar
(2) 0.0002 µ bar
(3) 0.005 µ bar
(4) 5.0 µ bar
496. (2) Least audible sound for most of the human ear is 2× 10–5 pascal. The generally accepted standard range of audible frequencies is 20 to 20,000 Hz.

### 497. Amount of water vapour (gaseous) in a given volume of air (cubic metre) is known as:

(1) Mixing ratio
(2) Relative humidity
(3) Absolute humidity
(4) Specific humidity
497. (3) The relative humidity of air at a given temperature is the ratio of mass of water vapour actually present in a certain volume of air to the mass of water vapour required to saturate the same volume of air at the same temperature, miltiplied by 100. Absolute Humidity refers to the amount of water vapour present in unit volume of air, expressed in grams per cubic metre.

### 498. When a running car stops suddenly, the passengers tends to lean forward because of:

(1) centrifugal force
(2) inertia of rest
(3) inertia of motion
(4) gravitational force
498. (3) When a running car stops suddenly, the passengers tend to lean forward due to inertia of motion. Inertia is that property of a body due to which it resists a change in its state of rest or of uniform motion.

### 499. Which of the following is a good conductor of heat but bad conductor of electricity ?

(1) mica
(2) asbestos
(3) celluloid
(4) paraffin wax
499. (1) Mica is a good conductor of heat but bad conductor of electricity.

### 500. For which of the following substances, the resistance decreases with increase in temperature?

(1) Pure silicon
(2) Copper
(3) Nichrome
(4) Platinum