# Physics GK Quiz-22

## Physics GK Quiz-22

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

### 421- Permissible noise level at Residential area during night time is :

(1) 45 dB (A)
(2) 55 dB (A)
(3) 75 dB (A)
(4) 80 dB (A)
421. (1) As per the norm, the permissible noise level in residential areas is 45 db during night time, 55 db during day and in commercial areas it is 55 db during night and 65 db during day.

### 422. Energy in reflected light :

(1) does not depends on the angle of incidence
(2) increases with the increase in angle
(3) decreases with the increase in angle of incidence
(4) becomes maximum for angle of incidence equal to 45°
422. (2) Reflected waves are simply those waves that are neither transmitted nor absorbed, but are reflected from the surface of the medium they encounter. The amount of incident-wave energy that is reflected from a surface depends on the nature of the surface and the angle at which the wave strikes the surface. The amount of wave energy reflected increases as the angle of incidence increases. The reflection of energy is the greatest when the wave is nearly parallel to the reflecting surface.

### 423- Which colour of light shows maximum deviation when passed through a prism ?

(1) White
(2) Red
(3) Violet
(4) Green
423. (3) The angle of deviation, by which the light of a particular wavelength gets deviated on passing through a medium, depends upon the refractive index of the medium, as encountered by that light wavelength. The smaller the wavelength of the passing light, the greater is the refractive index observed. As white light passes through a prism, the violet component, having the minimum wavelength observes the maximum refractive index for the prism and, thus, gets deviated to the maximum extent.

### 424- The best material for the core of a transformer is

(1) stainless steel
(2) mild steel
(3) hard steel
(4) soft iron
424. (4) Iron has a very large magnetic response: it greatly amplifies an applied magnetic field. The transformer’s ability to transfer energy depends on the strength of the magnetic field, so it is very helpful if the field is amplified. The input energy can then be lower while still having the same effect.

### 425. In AC circuits, AC meters measure

(1) mean values
(2) rms values
(3) peak values
(4) mean square values
425. (2) Voltages and currents for AC circuits are generally expressed as rms (root mean square) values. For a sine wave, the relationship between the peak and the rms average is: rms value = 0.707 peak value

### 426. When a light wave is reflected from a mirror, there is a change in its

(1) frequency
(2) amplitude
(3) wavelength
(4) velocity
426. (2) When a light wave is reflected from an object, it changes not only its amplitude but also its phase according to the properties of the object at a particular point. The velocity and momentum are just reversed in another direction.

### 427. Solar energy is due to

(1) fusion reactions
(2) fission reactions
(3) combustion reactions
(4) chemical reactions
427. (1) Nuclear Fusion Reaction is the process which is responsible for the sun to radiate energy in the form of light and heat commonly known as solar energy. Fusion occurs when hydrogen atoms fuse together under extreme heat and pressure to create a denser helium atom releasing, in the process, colossal amounts of energy.

### 428. The width of depletion layer of a P-N junction

(1) decreases with light doping
(2) increases with heavy doping
(3) is independent of applied voltage
(4) is increased under reverse bias
428. (4) The total width of the depletion region is a function of applied reverse-bias and impurity concentration. Forward bias decreases the depletion region width whilst reverse bias increases it.

### 429. A body absorbs heat most if it is

(1) black and rough
(2) black and smooth
(3) white and rough
(4) white and smooth
429. (1) A black body is an idealized physical body that absorbs all incident electromagnetic radiation,
regardless of frequency or angle of incidence. Another property is roughness. Sand is rough and black and so it is a good absorber.

### 430. Safety fuse wire used in domestic electrical appliances is made of metal of low

(1) Resistance
(2) Melting point
(3) Specific gravity
(4) Conductance
430. (2) The fuse wire is based on the Joules law of heating which says that when the electric current is allowed to pass through a conductor, the conductor heats up and is proportional to the square of current. The main object of using fuse wire in electric circuit is to provide protection against short circuit or overload current. For this purpose the material used as fuse wire should have high resistance and low melting point.

### 431. The following particles move with same kinetic energy. Which of them has maximum momentum ?

(1) Electron
(2) Proton
(3) Deutron
(4) Alpha Particle
431. (4) The formula for kinetic energy in terms of momentum for fundamental particles is basically just a quantized version of the classical formula, KE = p 2 m 2 , where KE is kinetic energy, p is momentum and m is the particle’s mass. In our case, Kinetic energy is constant, therefore p2 = 2m meaning that momentum is directly propor-tional to mass. The mass of particles in ascending order is: alpha, proton and electron. So Alpha particle will have the maximum momentum.

### 432. A bottle of sodalime is grasped by the neck and swung briskly in a vertical circle, Near which portion of the bottle do the bubbles collect?

(1) Near the bottom
(2) In the middle of the bottom
(3) Near the neck
(4) Bubbles remain distributed uniformly
432. (3) When the bottle of soda water is grasped by the neck and swung briskly in a vertical circle, the bubbles collect at the top of the bottle which is its neck. What flows in a carbonated drink is carbon dioxide gas. A carbonated beverage forms form bubbles when the dissolved carbon dioxide is depressurized to form emulsions at the top.

### 433. Water from soil enters into the root hairs owing to :

(1) Atmospheric pressure
(2) Capillary pressure
(3) Root pressure
(4) Osmotic pressure
433. (2) In plants, the transpiration stream is the uninterrupted stream of water, and other, which is
taken up by the roots and, via the xylem vessels, transported to the leaves where it will eventually
evaporate into the air/apoplast-interface of the substomatal cavity. It is driven in by capillary action
and in some plants root pressure. The main driving factor is the difference in water potential between
the soil and the substomatal cavity caused by transpiration.

### 434. The angle in which a cricket ball should be hit to travel maximum horizontal distance is :

(1) 60° with horizontal
(2) 45° with horizontal
(3) 30° with horizontal
(4) 15° with horizontal
434. (2) This has to do with the equation of a parabola or trajectory which is z = (tanq)x – q 2 (cos ) q x
2 . We can see that if the ball is fired at a 45 degree angle from the ground, the horizontal distance will be a maximum.

### 435. The minimum number of geostationary satellites needed for uninterrupted global coverage is :

(1) 3
(2) 2
(3) 4
(4) 1
435. (2) In theory, 2 satellites in diametrically opposite geosyn-chronous orbits could cover the planet. In order for the satellites to communicate, a minimum of 3 would be needed, each at a 60 degree angle to the others. At this point, the strength and quality of coverage increases proportionally to the number of satellites.

### 436. The best conductor of electricity among the following is :

(1) Copper
(2) Iron
(3) Aluminium
(4) Silver
436. (4) Copper: 9% less conductive than silver; aluminium is 10% less conductive than copper; while steel is the least conductive among the given options. The most electrically conductive metal is silver.

### 437. Flight Recorder is technically called :

(1) Dark box
(2) Blind box
(3) Black box
(4) Altitude meter
437. (3) A flight data recorder (FDR) is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. Another kind of flight recorder is the cockpit voice recorder which records conversation in the cockpit, radio communications between the cockpit crew and others
(including conversation with air traffic control personnel), as well as ambient sounds. Popularly
referred to as a “black box” by the media, the data recorded by the FDR is used for accident investigation as well as for analyzing air safety issues, material degradation and engine performance.

### 438. Which type of mirror is used in the head lights of vehicles ?

(1) Plane mirror
(2) Concave mirror
(3) Convex mirror
(4) Parabolic mirror
438. (2) Car head lights have concave mirrors because it collects and focuses as much as possible of the light from the bulb and send it out as a fairly tight beam in one direction only. The bulb of the head light is placed at the focal point. The reflected light is parallel and gives more visibility to the driver at night.

### 439. The height of a geo-stationary satellite from the Earth’s surface is approximately :

(1) 36,000 km
(2) 42,000 km
(3) 30,000 km
(4) None of these
439. (1) A geostationary orbit is a circular orbit 35,786 kilometres above the Earth’s equator and following the direction of the Earth’s rotation. Communications satellites and weather satellites are often given geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them, but can be pointed permanently at the position in the sky where they stay.

(1) air
(2) water
(3) sound
(4) soil