# Physics GK Quiz-14

## Physics GK Quiz-14

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

### 261. The sound produced by a bat is–

(1) audible
(2) subsonic
(3) infrasonic
(4) ultrasonic
261. (4) Although bats use echolocation to detect their prey, and find their way around in the dark, the sounds which they emit are ‘ultrasonic’, which is another way of saying they are beyond the range of normal human hearing. Ultrasound is a cyclic sound pressure wave with a frequency greater than the upper limit of the human hearing range. Ultrasound is thus not separated from “normal” (audible) sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy, young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.

### 262. When a bar magnet is cut into two equal halves, the pole strength of each piece –

(1) becomes double
(2) becomes half
(3) becomes zero
(4) remains the same
262. (4) The poles remains same whether the magnet is cut into two equal half or more and also pole strength remains same but magnetic moment reduces due to decrease in the length of the magnet. If a bar magnet is suspended by a thread, it will come to rest in a position close to the north-south direction. The end of the magnetic toward the north is called north pole (N-pole) of the magnet and the other end the south pole (S-pole). The poles of a magnet cannot be separated. If a bar magnet is broken into two parts, each part will be a complete magnet with the poles at its ends. No matter how many times a magnet is broken; each piece will contain N-pole at one end and S-pole at the other.

### 263. A new technology which provides the ability to create an artificial world and have people interact with it is called :

(1) Televirtuality
(2) Virtual reality
(3) Alternate reality
(4) 3-D reality
263. (2) Virtual reality (VR) is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds. Most current virtual reality environments are primarily visual experiences, displayed either on a computer screen or through special stereoscopic displays, but some simulations include additional sensory information, such as sound through speakers or headphones. Some advanced, haptic systems now include tactile information, generally known as force feedback, in medical and gaming applications.

### 264. Electrostatic precipitator is used to control –

(1) Air pollution
(2) Water pollution
(3) Solid waste
(4) Noise pollution
264. (1) An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators 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. In contrast to wet scrubbers which apply energy directly to the flowing fluid medium, an ESP applies energy only to the particulate matter being collected and therefore is very efficient in its
consumption of energy (in the form of electricity).

### 265. The time period of a seconds pendulum is

(1) 1 second
(2) 2 seconds
(3) 0·5 second
(4) 1·5 seconds
265. (2) A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 1/2 Hz. At standard gravity its length is 0.994 m.

### 266. Lakes freeze in cold countries in winter, leaving the water underneath at

(1) 0°C
(2) 0°F
(3) 4°C
(4) 4°F
266. (3) Lake ice cover is seasonal and occurs where average daily temperature is below the freezing point. Once formed the lake ice thickens over the course of the winter as the temperature gets colder. The lakes thermal structure prepares for ice with 0 (zero) degrees Celsius water at the surface and denser 4 degrees Celsius at the bottom. Once meteorological conditions provide colder air, relative to warmer water, the water does not get colder - instead ice forms.

### 267. Which one of the following determines the sharpness of image in a camera ?

(1) The aperture
(2) The exposure time
(3) The focal length of the lens
(4) Size of the camera
267. (1) Image quality is a characteristic of an image that measures the perceived image degradation (typically, compared to an ideal or perfect image). Imaging systems may introduce some amounts of distortion or artifacts in the signal, so the quality assessment is an important problem. Sharpness determines the amount of detail an image can convey. System sharpness is affected by the lens (design and manufacturing quality, focal length, aperture, and distance from the image center) and sensor (pixel
count and anti-aliasing filter).

### 268. In MRI machine, which one of the following is used?

(1) Sound wave
(2) ‘X’-ray
(3) Ultra-sound wave
(4) Magnetic wave
268. (4) Magnetic resonance imaging (MRI), nuclear magnetic resonance imaging (NMRI), or magnetic
resonance tomography (MRT) is a medical imaging technique used in radiology to visualize internal
structures of the body in detail. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body. An MRI scanner is a device in which the patient lies within a large, powerful magnet where the magnetic field is used to align the magnetization of some atomic nuclei in the body, and radio frequency fields to systematically alter the alignment of this magnetization. This causes the nuclei to produce a rotating magnetic field detectable by the scanner—and this information is recorded to construct an image of the scanned area of the body.

### 269. For a person having hypermetropia, the near point is

(1) greater than 25 cm
(2) greater than 50 cm
(3) less than 25 cm
(4) infinity
269. (1) For a hyper-metropic eye ,the near points shift away from the eye i.e. farther away from the normal near point (25cm). In a hypermetropic eye, the light is not bent sufficiently so that it focuses at a point behind the retina. Here a person sees well for distance but near vision is difficult and causes strain. Hence hypermetropic people are called long-sighted. To correct the hypermetropic eye, a plus lens is required so that the light can now focus on the retina.

### 270. Amount of water vapour in the atmosphere is measured in terms of

(1) Humidity
(2) Droplets
(3) Smog
(4) All of the above
270. (1) Humidity is the amount of water vapor in the air. Water vapor is the gas phase of water and is invisible. Humidity indicates the likelihood of precipitation, dew, or fog. Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table, used during summer weather. There are three main measurements of humidity: absolute, relative and specific.

### 271. Name the process of production of energy in the Sun

(1) Nuclear fission
(3) Nuclear fusion
(4) Ionization
271. (3) The source of the sun’s fuel is hydrogen and helium gases. Through a special chemical reaction, called nuclear fusion, the hydrogen gas is “burned” releasing an enormous amount of energy in the form of light and heat. In nuclear physics, 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. The opposite is true for the reverse process, nuclear fission.

### 272. A spherical ball made of steel when dropped in mercury container will

(1) sink in mercury
(2) will be on the surface of mercury
(3) will be partly immersed mercury
(4) will dissolve in mercury
272. (2) The density of steel usually ranges between 7.75 and 8.05 g/cm3 and the density of mercury is 13.534 g/cm3. Mercury is denser than steel this will mean that the buoyant force is large enough to float the steel ball. Different materials usually have different densities, so density is an important concept
regarding buoyancy, purity and packaging. Osmium and iridium are the densest known elements at
standard conditions for temperature and pressure but not the densest materials. Less dense fluids float
on more dense fluids if they do not mix.

### 273. The sounds having a frequency of 20 Hertz to 20,000 Hertz are known as

(1) Audible sounds
(2) Ultrasonics
(3) Infrasonics
(4) Megasonics
273. (1) An audio frequency is characterized as a periodic vibration whose frequency is audible to the average human. It is the property of sound that most determines pitch and is measured in hertz (Hz).The
generally accepted standard range of audible frequencies is 20 to 20,000 Hz, although the range
of frequencies individuals hear is greatly influenced by environmental factors. Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough.
Frequencies above 20,000 Hz can sometimes be sensed by young people.

### 274. Eclipses occur due to which optical phenomena?

(1) Reflection
(2) Refraction
(3) Rectilinear propagation
(4) Diffraction
274. (3) An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. Rectilinear propagation is a wave property which states that waves propagate (move or spread out) in straight lines. This property applies to both transverse and longitudinal as well as an
Electromagnetic wave. Even though a wave front may be bent (the waves created by a rock hitting a pond) the individual waves are moving in straight lines.

### 275. Pure water is bad conductor of electricity because it is

(1) feebly ionized
(2) not volatile
(3) a very good solvent
(4) a non-polar solvent
275. (1) Pure water is a covalent compound. It exists as simple discrete molecules and have a simple molecular structure. Hence, it does not exist as ions. Therefore, pure water cannot conduct electricity due to the absence of mobile ions and electrons. One instance that water can conduct electricity is when there are dissolved substance in it. Only then will water dissociate into hydrogen ions and hydroxide ions. The presence of mobile ions enables it to conduct electricity.

### 276. Gamma rays have greatest similarity with

(1) a-rays
(2) b-rays
(3) X-rays
(4) U.V.-rays
276. (3) Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as y, is electromagnetic radiation of high frequency and therefore high energy. Gamma rays are ionizing
radiation and are thus biologically hazardous. They are classically produced by the decay from high energy states of atomic nuclei (gamma decay), but are also created by other processes. X-radiation (composed of X-rays) is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV. They are shorter in wavelength than UV rays and longer than gamma rays.

### 277. In the absence of ozone layer, which rays will enter into atmosphere?

(1) Infrared
(2) Visible
(3) Ultraviolet
(4) X-rays
277. (3) The ozone layer is a layer in Earth’s atmosphere containing relatively high concentrations of ozone (O3). The ozone layer absorbs 97–99% of the Sun’s mediumfrequency ultraviolet light (from about 200 nm to 315 nm wavelength), which potentially damages exposed life forms on Earth. Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the sun. Extremely short or vacuum UV (10-100 nm) is screened out by nitrogen.

### 278. The filament of electric bulb is made up of :

(1) Copper
(2) Nichrome
(4) Tungsten
278. (4) An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light which produces light with a filament wire heated to a high temperature by an electric current passing through it, until it glows. Tungsten, also known as wolfram, is a chemical element. Tungsten’s many alloys have numerous applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target), electrodes in TIG welding, and superalloys.

### 279. When a vibrating tuning fork is placed on a table, a loud sound is heard. This is due to :

(1) reflection
(2) refraction
(3) forced vibrations
(4) damped vibrations
279. (3) The tendency of one object to force another adjoining or interconnected object into vibrational
motion is referred to as a forced vibration. In the case of the guitar string mounted to the sound box,
the fact that the surface area of the sound box is greater than the surface area of the string means
that more surrounding air particles will be forced into vibration. This causes an increase in the
amplitude and thus loudness of the sound. This same principle of a forced vibration is often demonstrated in a Physics classroom using a tuning fork. If the tuning fork is held in hand and hit with a rubber mallet, a sound is produced as the tines of the tuning fork set surrounding air particles into vibrational motion. The sound produced by the tuning fork is barely audible to students in the back rows of the room. However, if the tuning fork is set upon the whiteboard panel or the glass panel of the overhead projector, the panel begins vibrating at the same natural frequency of the tuning fork.

### 280. Light houses are places with powerful lights to :

(1) guide and resolve traffic jams in crowded metro-cities during nights.
(2) guide and help large crowds at religious gathering during nights.
(3) indicate to the incoming warships, the location of a harbour during night.
(4) guide and warn the ships coming from different directions in the ocean.