# Physics GK Quiz-7

## Physics GK Quiz-7

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

### 121. Which of the following pairs of physical quantities have the same dimensions?

(1) Force and Power
(2) Work and Power
(3) Work and Energy
(4) Momentum and Power
121. (3) The term energy is used to describe the capacity of a system to do work on another system. Energy of all types (Surface Tension, Kinetic, Potential etc.) have the same dimension and unit as that of Work. Both energy and work have the same dimensional formula of M1L2T–2. In the SI system, both have the same units of Newton meter.

### 122. Magnetism in materials is due to

(1) electrons at rest
(2) circular motion of electrons
(3) protons at rest
(4) all neutrons at rest
122. (2) Magnetism is a property of materials that respond to an applied magnetic field. Permanent magnets have persistent magnetic fields caused by ferromagnetism. That is the strongest and most familiar type of magnetism. However, all materials are influenced varyingly by the presence of a magnetic field. When a material is put in a magnetic field, the electrons circling the nucleus will experience, in addition to their Coulomb attraction to the nucleus, a Lorentz force from the magnetic field. Depending on which direction the electron is orbiting, this force may increase the centripetal force on the electrons, pulling them in towards the nucleus, or it may decrease the force, pulling them away from the nucleus. This effect systematically increases the orbital magnetic moments that were aligned opposite the field, and decreases the ones aligned parallel to the field (in accordance with Lenz’s law). This results in a small bulk magnetic moment, with an opposite direction to the applied field.

### 123. ‘Short-sight’ in human eye can be corrected by using proper

(1) convex lens
(2) concave lens
(3) cylindrical lens
(4) bifocal lens
123. (2) Myopia is commonly known shortsighted. It is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it. This causes the image that one sees when looking at a distant object to be out of focus but in focus when looking at a close object. Eye care professionals most commonly correct myopia through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, though there are cases of associated side effects. The corrective lenses have a negative optical power (i.e. are concave) which compensates for the excessive positive diopters of the myopic eye.

### 124. What is the reason for twinkling of stars ?

(1) Dispersion of light
(2) Total internal reflection
(3) Atmospheric reflection
(4) Atmospheric refraction
124. (4) Scintillation or twinkling is generic terms for variations in apparent brightness or position of a
distant luminous object viewed through a medium. If the object lies outside the Earth’s atmosphere, as in the case of stars and planets, the phenomenon is termed astronomical scintillation; within the
atmosphere, the phenomenon is termed terrestrial scintillation. As one of the three principal factors
governing astronomical seeing, atmospheric scintillation is defined as variations in illuminance
only. Scintillation does not cause images of planets to flicker. Most scintillation effects are caused by
anomalous refraction caused by small-scale fluctuations in air density usually related to temperature gradients.

### 125. The instrument for measuring intensity of earthquakes is called

(1) Ediograph
(2) Pantagraph
(3) Ergograph
(4) Seismograph
125. (4) Seismometers are instrument that measures motion of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions and other seismic sources. Records of seismic waves allow seismologists to map the interior of the earth and locate and measure the size of these different sources. Seismograph is another Greek term meaning to draw siesmo waves. It is often used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined than to modern systems, in which these functions are separated.

### 126. Which one of the following animals can hear ultrasonic sound ?

(1) Rat
(2) Squirrel
(3) Cat
(4) Bat
126. (4) 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. Bats use a variety of ultrasonic ranging (echolocation) techniques to detect their prey. They can detect frequencies beyond 100 kHz, possibly up to 200 kHz.

### 127. The source of the sun’s energy is the process of

(1) photoelectric emission
(2) nuclear fission
(3) nuclear fusion
(4) thermionic emission
127. (3) The Sun formed about 4.6 billion years ago from the gravitational collapse of a region within a large molecular cloud. Most of the matter gathered in the center, while the rest flattened into an orbiting disk that would become the Solar System. The central mass became increasingly hot and dense, eventually initiating thermonuclear fusion in its core. It is thought that almost all other stars form by this process.

### 128. A multimeter is used to measure

(1) current
(2) voltage
(3) resistance
(4) All of the above
128. (4) A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. Multimeters may use analog or digital circuits—analog multimeters (AMM) and digital multimeters (often abbreviated DMM or DVOM.) A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.

### 129. Which of the following is used to split white light into different colours ?

(1) Glass slab
(2) Convex lens
(3) Concave lens
(4) Prism
129. (4) In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. At least two of the flat surfaces must have an angle between them. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use “prism” usually refers to this type. A prism can be used to break light up into its constituent spectral colours (the colours of the rainbow). Prisms can also be used to reflect light, or to split light into components with different polarizations. Prisms are sometimes used for the internal reflection at the surfaces rather than for dispersion.

### 130. Nuclear reactors used to produce electricity are based on

(1) nuclear fission
(2) nuclear fusion
(3) cold fusion
(4) superconductivity
130. (1) A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid (water or gas), which runs through turbines that power either ship’s propellers or generators. Some produce isotopes for medical and industrial use, and some are run only for research. Just as conventional power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, nuclear reactors convert the thermal energy released from nuclear fission.

### 131. Submerged objects can be located using

(2) sonar
(3) quasar
(4) pulsar
131. (2) Sonar (originally an acronym for Sound Navigation And Ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of “targets” in the water. The term
sonar is also used for the equipment used to generate and receive the sound.

### 132. Which one of the following instruments is used to study dispersion of light ?

(1) Microscope
(2) Telescope
(3) Spectrometer
(4) Photometer
132. (3) Dispersion occurs when different frequencies of light have different phase velocities, due either to material properties (material dispersion) or to the geometry of an optical waveguide (waveguide
dispersion). A spectrometer (spectro-photometer, spectrograph or spectroscope) is an instrument used
to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in
spectroscopic analysis to identify materials. The variable measured is most often the light’s intensity
but could also, for instance, be the polarization state.

### 133. A fountain pen works on the principle of

(1) flow of liquids from higher to lower potential
(2) capillary action
(3) Bernoulli’s principle
(4) Viscosity of liquids
133. (2) A fountain pen is a nib pen that, unlike its predecessor the dip pen, contains an internal
reservoir of water-based liquid ink. The pen draws ink from the reservoir through a feed to the nib and
deposits it on paper via a combination of gravity and capillary action. Capillary action, or capillarity, is the ability of a liquid to flow in narrow spaces without the assistance of, and in opposition to external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper, in some non-porous materials such as liquefied carbon fiber, or in a cell.

### 134. Pycnometer is an instrument used to measure the

(1) density
(3) intensity of earthquake
(4) high temperatures
134. (1) A gas pycnometer is a laboratory device used for measuring the density — or more accurately the volume — of solids, be they regularly shaped, porous or non-porous, monolithic, powdered, granular or in some way comminuted, employing some method of gas displacement and the volume-pressure relationship known as Boyle’s Law. A gas pycnometer is also sometimes referred to as a helium pycnometer. While pycnometer (of any type) is recognized as density measuring devices they are in fact devices for measuring volume only.

### 135. Fibre optics work on the principle of

(1) scattering of light
(2) total internal absorption
(3) total internal reflection
(4) optical rotation
135. (3) An optical fiber (or optical fibre) is a flexible, transparent fiber made of glass (silica) or plastic,
slightly thicker than a human hair. It functions as a waveguide, or “light pipe”, to transmit light between
the two ends of the fiber. The field of applied science and engineering concerned with the design and
application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic
communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference.

### 136. A decibel is

(1) a musical instrument
(2) the wavelength of noise
(3) a musical note
(4) a measure of sound level
136. (4) The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities. A decibel is one tenth of a bel, a seldom-used unit commonly used to measure sound level. The decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics, electronics, and control theory. In electronics, the gains of amplifiers, attenuation of signals, and signalto-noise ratios are often expressed in decibels.

### 137. Remote-sensing device has an inbuilt source of

(1) X-ray
(2) g-ray
(3) ultraviolet ray
(4) infrared ray
137. (4) Infrared imaging is used extensively for military and civilian purposes. Military applications include target acquisition, surveillance, night vision, homing and tracking. Non-military uses include thermal efficiency analysis, environmental monitoring, industrial facility inspections, remote temperature sensing, short-ranged wireless communication, spectro-scopy, and weather forecasting. Infrared astronomy uses sensor-equipped telescopes to penetrate dusty regions of space, such as molecular clouds; detect objects such as planets, and to view highly red-shifted objects from the early days of the universe. There are two main types of remote sensing: passive remote sensing and active remote sensing. Reflected sunlight is the most common source of radiation measured by passive sensors. Examples of passive remote sensors include film photography, infrared, charge-coupled devices, and radiometers.

### 138. The atmosphere is heated mainly by

(1) Insolation
(2) Conduction
(4) Convection
138. (3) Changes in weather involve air movements, formation of clouds, and precipitation. Energy is
needed to make all these things happen. That energy comes from the sun. Heat energy enters and moves
through the atmosphere in three different ways. One way that heat energy is transferred is radiation. Hot
bodies such as the sun radiate their energy mainly in the form of short waves. These short waves are
seen as visible light. Cooler bodies such as Earth radiate their energy as longer waves.

### 139. A device used for converting a.c. into d.c. is called

(1) transformer
(2) recticfier
(3) induction coil
(4) dynamo
139. (2) A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, solid-state diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. Rectifiers have many uses, but are often found serving as components of DC power supplies and high-voltage direct current power transmission systems. Rectification may serve in roles other than to generate direct current for use as a source of power.

### 140. Energy of Ultraviolet rays is great than

(1) Infra–red rays
(2) Gamma rays
(3) X–rays
(4) Cosmic rays