# Physics GK Quiz-2

## Physics GK Quiz-2

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

### 21. Surface tension in a liquid is due to :

(2) Cohesive force between molecules
(3) Gravitational force between molecules
(4) Electrical force between molecules.
21. (2) Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. This property is caused by cohesion of similar molecules, and is responsible for many of the behaviors of liquids. It is revealed, for example, in the floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects (e.g. water striders) to run on the water surface.

### 22. A circular plate, a cube and a sphere, all made up of same material and having the same mass, are heated to 300°C and left in a room. Which of them will have the slowest rate of cooling?

(1) Circular plate
(2) Cube
(3) Sphere
(4) All will cool at the same rate
22. (3) In the late of 17th century British scientist Isaac Newton studied cooling of bodies. Experiments
showed that the cooling rate is approximately proportional to the difference of temperatures between the heated body and the environment. This fact can be written as the differential relation :
dQ dt A T T = a b g S - , where A is the surface area of the body through which the heat is transferred, T is the temperature of the body, TS is the temperature of the surrounding environment, á is the heat transfer coefficient depending on the geometry of the body, state of the surface, heat transfer mode, and other factors. Surface area or volume ratio is an important influence on temperature control. For same volume sphere has minimum surface area, while circular plate has maximum surface area. So sphere cools slowest and plate cools fastest.

### 23. Optic fibres are used in :

(1) CAT scans
(2) X-ray photos
(3) Ultrasound scans
(4) Endoscopy
23. (4) Optical fibres are used in endoscopic instruments that enable doctors to view internal body parts
without having to perform surgery. Fernando Alves Martins of Portugal invented the first fiber optic
endoscope in 1963-64. Further innovations included using additional fibres to channel light to the objective end from a powerful external source, thereby achieving the high level of full spectrum illumination that was needed for detailed viewing, and colour photography. The previous practice of a small filament lamp on the tip of the endoscope had left the choice of either viewing in a dim red light or increasing the light output - which carried the risk of burning the inside of the patient. Alongside the advances to the optical side, the ability to ‘steer’ the tip was developed, as well as innovations in remotely operated surgical instruments contained within the body of the endoscope itself. This was the beginning of “key-hole surgery” as we know it today.

### 24. Two waves, each of amplitude 1.5 mm and frequency 10 Hz, are travelling in opposite direction with a speed of 20 mm/s. The distance in mm between adjacent nodes is :

(1) 1.0
(2) 1.2
(3) 1.5
(4) 2.0
24. (1) Since the amplitudes, frequency and the speed of both the waves are in same, hence the wavelength of the composite wave will be the same as the single wave. The distance between the adjacent nodes will be a 2 , Speed of the wave, i.e., V = nl. Or, 20 = 10l. So, l = 2 mm. Therefore, a 2
= 1 mm

### 25. The snow on the mountains does NOT melt all at once when it is heated by the sun because:

(1) it becomes very hard
(2) it reflects most of the heat from the sun
(3) it has a low specific heat capacity
(4) it has a high latent heat of fusion
25. (2) Newly formed snow reflects about 90 per cent of the sunlight that falls upon it. This means that the sun is powerless to melt clean snow. And when snow does melt, it is not because of the sunlight. Snow does not melt on a spring day because of the sun’s heat. It melts because of the warm air from the sea.

### 26. A person standing on a railway platform listens to the whistles of arriving and departing trains. The whistle heard is

(1) the same in both cases in all respects
(2) of higher intensity when train arrives
(3) of higher pitch when train arrives
(4) of higher pitch when train departs
26. (3) Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. (Sound can propagate through solids as well, but there are additional modes of propagation). Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz. In air at standard temperature and pressure, the corresponding wavelengths of sound waves range from 17 m to 17 mm. During propagation, waves can be reflected, refracted, or attenuated by the medium. Now if we consider these cases, then the train which is arriving towards us having whistles of higher pitch because it propagates through a medium which is coming towards us but the train which is leaving propagating trough a medium moving further away from the listener and thus produced whistle of lower pitch.

### 27. Holography is a technique of

(1) recording a permanent, sharp two diimensional black and white or multicolour photograph
(2) recording a permanent three dimensional multicolour photograph
(3) recording a permanent three dimensional black and white photograph
(4) recording a permanent three dimensional photograph of a given single colour or a multicolour
27. (4) Holography is a technique which enables threedimensional images to be made. It involves the use of a laser, interference, diffraction, light intensity recording and suitable illumination of the recording. The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the image appear three-dimensional. The holographic recording itself is not an image; it consists of an apparently random structure of varying intensity, density or profile. Holography is a technique that enables a light field, which is generally the product of a light source scattered off objects, to be recorded and later reconstructed when the original light field is no longer present, due to the absence of the original objects.

### 28. The velocity of sound in moist air is more than in dry air because the moist air has

(1) less density than dry air.
(2) less pressure than dry air.
(3) more pressure than dry air.
(4) more density than dry air.
28. (1) The density of dry air is more than that of moist air (when moisture is removed from air, its density increases). The speed of sound in a medium is inversely proportional to the square root of its density. Therefore, the speed of sound in moist air is more than that in dry air.

### 29. An ice block with a piece of lead embeded in it floats in water. If ice melts the water level

(1) Rises
(2) Falls
(3) Remains same
(4) Falls first and then rises
29. (2) If r1 is the density of the lead piece of volume v, the volume of water displaced by the ice block and the lead piece while floating is Vw = (V–v) r1 + v r1. When the ice melts, the lead piece sinks in water since r1 is greater than the density of water. The water produced by the melted ice has the volume
(V-v) r1 and the volume displaced by the lead piece is v. So, the total volume of the water produced by ice and that displaced by the lead piece is V w1 = (V–v) r1+ v r1< V w. So, the water level goes down.

### 30. The velocity of heat radiation in vacuum is

(1) Equal to that of light
(2) Less than that of light
(3) Greater than that of light
(4) Equal to that of sound
30. (1) Electrons are generally responsible for heat conduction. The phonons (vibrations of the nuclei)
also play a part, depending on the temperature of the medium. It depends on the specific conductor
you’re using. At some point, in a vacuum, the electrons have to be excited enough to spit out photons, which are Electromagnetic radiation, which in a vacuum should go on forever at the speed of light theoretically.

### 31. The plastic material commonly used for making gear wheels is

(1) Polyesters
(2) Nylons
(3) Bakelit
(4) Polystyrene
31. (2) Popular materials for plastic gears are acetal resins such as DELRIN, Duracon M90; nylon resins such as ZYTEL, NYLATRON, MC901 and acetal copolymers such as CELCON. The physical and mechanical properties of these materials vary with regard to strength, rigidity, dimensional stability, lubrication requirements, moisture absorption, etc .A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source.

### 32. Ultra violet radiations of the Sun do not reach the earth because, earth’s atmosphere is surrounded by

(1) Carbon dioxide
(2) Ammonia
(3) Chlorine
(4) Ozone
32. (4) The ozone layer absorbs 97–99% of the Sun’s medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength), which potentially damages exposed life forms on Earth. Ozone is formed from di-oxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout the Earth’s atmosphere. In total, ozone makes up only 0.6 parts per million of the atmosphere. Ozone is a powerful oxidant (far more so than di-oxygen) and has  many industrial and consumer applications related to oxidation. This same high oxidizing potential, however, causes ozone to damage mucus and respiratory tissues in animals, and also tissues in plants, above concentrations of about 100 parts per billion. This makes ozone a potent respiratory hazard and pollutant near ground level.

### 33. “Curie” is unit of :

(2) Temperature
(3) Heat
(4) Energy
33. (1) Curie, in physics, unit of activity of a quantity of a radioactive substance, named in honour of the French physicist Marie Curie. One curie (1 Ci) is equal to 3.7 × 1010 becquerel (Bq). Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. Because the nucleus experiences the intense conflict between the two strongest forces in nature, it should not be surprising that there are many nuclear isotopes which are unstable and emit some kind of radiation. The most common types of radiation are called alpha, beta, and gamma radiation, but there are several other varieties of radioactive decay.

### 34. Which of the following is used in oven ?

(1) X-rays
(2) UV rays
(3) Microwaves
34. (3) An oven that uses micro radiation waves as a source of heat in order to cook food as opposed to a fire source. Conceptualized in 1946, Dr. Perry Spencer allegedly discovered the heating properties
of microwaves while studying the magnetron. A microwave oven, often colloquially shortened to
microwave, is a kitchen appliance that heats food by dielectric heating accomplished with radiation used to heat polarized molecules in food. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25–38 mm of a dense (high water content) food item; food is more evenly heated throughout (except in thick, dense objects) than generally occurs in other cooking techniques. A microwave oven works by passing non-ionizing microwave radiation, usually at a frequency of 2.45 gigahertz (GHz)—a wavelength of 122 millimetres (4.80 in)—through the food. Microwave radiation is between common radio and infrared frequencies.

### 35. When heated from 00 to 100C volume of a given mass of water will :

(3) Increase and then will decrease
(4) Decrease and then will increase
35. (4) When heated from 00 to 100 C volume of a given mass of water will first decrease and then increase. If the word “ice” or “solid” is not mentioned, the word “water” means liquid water. Water vapor can be produced from the evaporation or boiling of liquid water. So the volume first decreases and then increases again when water droplets form from the vapours due to stoppage of heat.

### 36. Energy is continuously created in the sun due to:

(1) nuclear fusion
(2) nuclear fission
36. (1) The central mass of the sun becomes increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is thought that almost all other stars form by this process. nuclear fusion is a nuclear reaction in which two or more atomic nuclei join together, or “fuse”, to form a single heavier nucleus. During this process, matter is not conserved because some of the mass of the fusing nuclei is converted to energy which is released. Fusion is the process that powers active stars. The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy, while the fusion of nuclei heavier than iron absorbs energy.

### 37. In electronics what comes under tank circuit ?

(1) Resistance and capacity
(2) Resistance and inductance
(3) Capacity and inductance
(4) Resistance, capacity and inductance
37. (3) An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit, consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C. When connected together, they can act as an electrical resonator, an electrical analogue of a tuning fork, storing energy oscillating at the circuit’s resonant frequency. When connected together, they can act as an electrical resonator; an electrical analogue of a tuning fork, storing energy oscillating at the circuit’s resonant frequency. An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance.

### 38. Coolis tube is used to produce

(2) Micro waves
(3) X-rays
(4) Gama rays
38. (3) X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light. X-ray tubes evolved from experimental Crookes tubes with which X-rays were first discovered in the late 19th century, and the availability of this controllable source of X-rays created
the field of radiography, the imaging of opaque objects with penetrating radiation.

### 39. Which of the following is used for regulated electric supply ?

(1) Zener diode
(2) Junction diode
(3) Gun diode
(4) Tunnel diode
39. (1) The Zener diode is like a general-purpose signal diode. When based in the forward direction it behaves just like a normal signal diode, but when a reverse voltage is applied to it, the voltage remains constant for a wide range of currents and hence widely used for regulated electric supply. The device was named after Clarence Zener, who discovered this electrical property. Many diodes described as “Zener” diodes rely instead on avalanche breakdown as the mechanism. Common applications include providing a reference voltage for voltage regulators, or to protect other semiconductor devices from momentary voltage pulses. Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits.

### 40. The source of the Sun’s energy is the process of

(1) Photoelectric emission
(2) Nuclear fission
(3) Nuclear fusion
(4) Thermionic emission