# Physics GK Quiz-17

## Physics GK Quiz-17

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

### 321. Which of the following events occurred first ?

(1) Albert Einstein propounded the General Theory of Relativity
(2) Max Planck unveiled the Quantum Theory
(3) Marconi first transmitted a wireless signal
(4) Madame Marie Curie became the first woman Nobel Prize winner
321. (2) General Theory of Relativity: a theory of gravitation developed by Einstein in the years 1907–1915; Quantum Theory of Max Planck: 1900; Transmission of wireless signal by Marconi: first Atlantic wireless transmission on December 11, 1901; and Madame Curie becoming the first woman Nobel Prize winner: shared her 1903 Nobel Prize in Physics with her husband Pierre Curie.

### 322. The audio signals of TV are

(1) Amplitude modulated
(2) Frequency modulated
(3) Unmodulated
(4) Velocity modulated
322. (2) In analogue television, the sound portion of a broadcast is invariably modulated separately from the video. Most commonly, the audio and video are combined at the transmitter before being presented to the antenna, but in some cases separate aural and visual antennas can be used. In almost all cases, standard wideband frequency modulation is used.

### 323. Red light is used for signals because it has

(1) long wavelength
(2) high intensity
(3) high frequency
(4) low refraction in the medium
323. (1) Red is the international colour of stop signs and stop lights on highways and intersections because it is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a colour. Red has the highest wavelength of all the colours and is able to travel the longest distance through fog, rain, and the alike.

### 324. Woollen cloth protects the body from cold because

(1) it is a good conductor of heat
(2) it is a poor conductor of heat
(3) external heat rays enter into the body through the woollen cloth
(4) it reflects heat
324. (2) It is just because woolen clothes have fibres and between those fibres air is trapped which reduces heat loss. It reduces heat loss because it is an insulator or poor conductor of heat.

### 325. The owl can see most clearly in total darkness because

(1) it has squint eyes
(2) it has large eyes with orbs directed forward, giving it binocular sight
(3) it has light bulbs in its eyes provided by nature
(4) it produces infrasonic sounds
325. (2) Because of their eyes, an owl can see much better in the dark than we can. Owls have very large eyes which maximize light gathering in conditions of minimum light, thereby enabling them to see at night. The orbs of their eyes are directed forward, giving them binocular vision. They are able to see their prey in a three-dimensional manner. However, an owl’s eye cannot rotate.

### 326. Damp clothes are dried in spin dryers by the action of

(1) centripetal forces
(2) centrifugal forces
(3) central forces
(4) non central forces
326. (2) The spin dryer is probably the most familiar centrifuge. The spin dryer of a washing machine
removes excess water from the clothing by rotating at a high speed. The high speed of rotation creates a
high centrifugal force for the water in the clothing which causes it to be pulled to the outside of the
spinning portion of the washing machine and away from the clothes.

### 327. Which colour of light shows maximum deviation when passed through a prism ?

(1) Red
(2) Green
(3) Violet
(4) Yellow
327. (3) When passed through a prism violet colour of light shows maximum deviation. As white light passes through a prism, the voilet component, having the minimum wave length observes the maximum
refractive index for the prism and, thus, gets deviated to the maximum extent.

### 328. Tape recorder should not be kept near one of the following things :

(1) Clock
(2) Magnet
(3) Electrical switchboard
328. (2) The cassette tape contains a magnetic strip wound around two spools. Tiny magnetic particles are randomly scattered throughout the tape. A tape recorder should not be kept near a magnet as the
latter can cause the magnetic material to be pushed and pulled out of place. Rearranging the magnetic
particles erases the sound.

### 329. When a person sitting on a swing stands up on the swing, the frequency of oscillation

(1) decreases
(2) increases
(3) becomes infinite
(4) does not change
329. (2) In Simple Harmonic Motion, the frequency of the oscillation (f) is the number of oscillations per second which is expressed as f = 1 T where T is the time period (the time for the oscillator to complete one cycle). Now, when a person sitting on a swing stands up on the swing, the effective length of the swing decreases. When length decreases, the time period also decreases. Since frequency of oscillation is inversely proportion to time period, it increases in the present case of man standing up on the swing.

### 330. Night photography and photopraphy in mist and fog are possible using

330. (2) Infrared is used in night vision equipment when there is insufficient visible light to see. Night vision devices operate through a process involving the conversion of ambient light photons into electrons which are then amplified by a chemical and electrical process and then converted back into visible light.

### 331. The blue colour of water in the sea is due to

(1) absorption of other colours except blue by water molecules
(2) scattering of blue light by water molecules
(3) reflection of blue light by impurities in sea water
(4) reflection of blue sky by sea water
331. (1) Almost all sunlight that enters the ocean is absorbed, except very close to the coast. The red, yellow, and green wavelengths of sunlight are absorbed by water molecules in the ocean. The reason the ocean is blue is due to the absorption and scattering of light. The blue wavelengths of light are scattered, similar to the scattering of blue light in the sky but absorption is a much larger factor than scattering for the clear ocean water. In seawater, absorption is strong in the red and weak in the blue, thus red light is absorbed quickly in the ocean leaving blue.

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

(1) Celluloid
(2) Rubber
(3) Asbestos
(4) Mica
332. (4) Good conductors of heat are good conductors of electricity. Mica is an exception which although being a good conductor of heat and a bad conductor of electricity. It is commonly used in insulation of electricity between high heat generating transistors and their heat sink and or chassis to prevent grounding out of component and to assist in the transfer of the generated heat to the heat sink or chassis for dissipation.

### 333. An aircraft can perform aerobatic manoeuvres in a vertical loop because of

(1) gravity
(2) centripetal force
(3) weight
(4) centrifugal force
333. (1) It happens because of gravity. A key feature of super maneuvering aircrafts is a high thrust-to-weight ratio; that is, the comparison of the force produced by the engines to the aircraft’s weight, which is the force of gravity on the aircraft. A thrust-to-weight ratio greater than 1:1 is a critical threshold, as it allows the aircraft to maintain and even gain velocity in a nose-up attitude; such a climb is based on sheer engine power, without any lift provided by the wings to counter gravity, and has become crucial to aerobatic maneuvers in the vertical loop.

### 334. A photostat machine works on

(1) electromagnetic image making
(2) electrostatic image making
(3) magnetic image making
(4) thermal image making
334. (2) A photocopier uses electrostatic charge to produce a copy. The original document is placed onto a sheet of glass. An image of this page is projected onto a positively charged drum. The drum has a coating which conducts electricity when light falls on it. The parts of the drum which are lit by the projected image lose their electrostatic charge when they start to conduct.

### 335. Steam at 1000C causes more severe burns than water at 100° C because

(1) steam has no specific heat capacity
(2) steam has latent heat of vaporisation
(3) water has no specific heat capacity
(4) water has latent heat of fusion
335. (2) It is because steam releases its latent heat as it condenses, which is substantial. The heat of
vaporization of steam is over 2000 J per gram. And when it releases that it’s then 100 degree water, the
same as boiling water.

### 336. To measure the speed of an approaching car a police officer shines

(1) light waves on it
(2) microwaves on it
(4) ultra high frequency waves on it
336. (3) Radar, which stands for radio detection and ranging, is a system that uses reflected radio waves to detect objects and measure their distance and speed. For example, police use radar to calculate the speed of cars.

### 337. During hot weather, the fan produces a feeling of comfort. This is because

(1) fan supplies cool air
(2) fan cools the air
(3) our perspiration evaporates rapidly
(4) conductivity of air increases
337. (3) Fans make the air more comfortable for two reasons: (a) by moving the air, they blow away body heat and evaporate sweat, cooling the body, and (b) they also mix the cooler air near the floor with the warmer air by people’s faces.

### 338. Forged documents are detected by

(1) ultraviolet rays
(2) infra-red rays
(3) beta rays
(4) gamma rays
338. (1) Old postcards, books, signs, photos and other paper products made before the late 1930s rarely
glow under a black light. Chemical bleaches and dyes used in modern papers will fluoresce under ultraviolet light. Knowing this helps to detect forged documents and distinguish reproductions in all types of ephemera.

### 339. Rainbow is seen after rain because of hanging molecules of water which act as

(1) lenses
(2) mirrors
(2) prisms
(4) slabs
339. (2) In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. In a rainbow, raindrops in the air act as tiny prisms. Light enters the raindrop, reflects off of the side of the drop and exits. In the process, it is broken into a spectrum just like it is in a triangular glass prism.

### 340. Which of the following is a result of Surface tension ?

(1) Gravitational pull
(2) Viscosity
(3) Capillary action