# Physics GK Quiz-18

## Physics GK Quiz-18

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

### 341. Lightning is caused due to

(1) electric power
(2) electric discharge
(3) electric leak
(4) electric pressure
341. (2) Lightning is a discharge of electrical energy that builds up within a storm. The charges develop because a storm causes air to move around which rubs against itself to generate electrical charges. Eventually the charge increases to a point where the electricity can flow through the air. Once an electric discharge starts it provides a better path for more electrical flow than normal air due to ionization which results in a sudden, large and fast discharge.

### 342. Sprayer functions on

(1) Bernouli’s principle
(2) Archemede’s principle
(3) Pascal’s law
(4) Floatation principle
342. (1) Bernoulli’s principle states that as the speed of a moving fluid (liquid or gas) increases, the pressure within the liquid decreases. In the case of a sprayer, when the plunger is pushed in, the air flows at a high velocity through a nozzle, creating a region of low pressure above the metal tube. The higher pressure of the atmospheric air causes the liquid to rise up to the metal tube and come out as spray.

### 343. The device which transfer the signal from low resistance region to high resistance region is

(1) diode
(2) transistor
(3) capacitor
(4) inductor
343. (2) A transistor transfers a signal from a low resistance to high resistance. It has two PN-junctions: one junction is forward biased and other junction is reverse biased having low resistance path and high resistance path respectively. The weak signal is introduced in the low resistance, circuit and output is taken from the high resistance circuit.

### 344. A bird sitting on a high tension electric wire does not get electrocuted because

(1) it has high resistance
(2) the body is earthed
(3) it does not form a closed path for the flow of current
(4) its feet are good insulators
344. (3) Electricity travels from a place of high voltage to low voltage, just as water travels from high elevation to low elevation. A bird, or any living thing, that touches a wire (where electricity is moving from high voltage to low voltage) and also touches the ground (a place with no voltage) creates a path that allows the electricity to travel through that body and into the place with no voltage. When  electricity travels through a body in this fashion, electrocution takes place, and the bird can die.

### 345. The wall of a dam is broader at the base

(1) because streamlining is required
(2) to withstand pressure that increases with depth
(3) to withstand pressure that increases in a horizontal plane
(4) to withstand pressure that is increased with atmospheric pressure
345. (2) Dams are built broader at the base for two reasons. The first is because it needs to be stable enough to support the dam, and two, the bottom of the dam needs to be able to deal with the increased pressure of the water, as you get further down. Particular to dams, at the lower part of the structure the lower levels of water are at higher pressure than the upper levels of the water.

### 346. Which of the following is arranged in order of decreasing conductivity?

(1) Copper, Aluminium, Steel, Silver
(2) Aluminium, Silver, Copper, Steel
(3) Copper, Silver, Aluminium, Steel
(4) Silver, Copper, Aluminium, Steel
346. (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.

### 347. Which of the following liquids is most viscous?

(1) Oil
(2) Milk
(3) Water
(4) Petrol
347. (1) Informally, viscosity is the quantity that describes a fluid’s resistance to flow. It is dependent on temperature. Viscosity of the different fluids (in cP) is as follows: Edible Oil: 20 to 60; Milk: approximately 1.0; Water: 0.894; and Petrol: around 0.82 to 0.95 cP.

### 348. Radio activity is due to

(1) unstable nucleus
(2) stable nucleus
(3) stable electronic configuration
(4) stable electronic configuration
348. (1) Radioactivity is caused by unstable nuclei trying to become stable by emitting particles and or energy. The nuclei of radioactive substances are unstable due to an unstable ratio of protons to neutrons.

### 349. Which conservation principle is applicable in the case of the motion of a rocket?

(1) Conservation of mass
(2) Conservation of charge
(3) Conservation of momentum
(4) Conservation of energy
349. (3) The motion of a rocket is an application of Newton’s third law of motion and law of conservation of linear momentum. The operation of a rocket illustrates the conservation of momentum. Just before launching, the momentum of the rocket is zero. When the rocket is fired, it forces a jet of hot gases with a high velocity through the nozzle. The jet of gases acquires a momentum downwards. Hence, the rocket acquires a momentum of equal magnitude in opposite direction. Thus the rocket moves upwards.

### 350. It is easier to carry two buckets of water in one hand each, than to carry only one in one hand because

(1) weights of buckets are balanced
(2) centre of gravity falls within the body
(3) centre of gravity and centre of equilibrium fall within the feet
(4) resultant weight of buckets is zero
350. (3) When the buckets containing equal amount of water are held in both hands, weight is spaced out more evenly than it would be if one had to carry a single bucket. For balancing the weight, the centre of gravity and the centre of equilibrium should fall, in the present case, within the feet.

### 351. The surface tension of water on adding detergent to it

(1) increases
(2) decreases
(3) no change
(4) becomes zero
351. (2) In the solid and liquid phase, water molecules are bonded to each other by virtue of an interaction between hydrogen atoms on one molecule and the oxygen atom of another — the process is referred to as “hydrogen bonding.” The result is a kind of “skin” on liquid water’s surface. When Soaps and detergents are added to water, they weaken the strength of the skin by interfering with hydrogen bonding between water molecules because the polar end of the soap or detergent is also attracted to the water.

### 352. In a refrigerator, the cooling system should always be

(1) at the top
(2) at the bottom
(3) at the middle
(4) can be anywhere
352. (2) The compressor is the motor (or engine) of the cooling system. It is normally at the bottom of the refrigerator in the back. The compressor runs whenever the refrigerator thermostat calls for cooling.

### 353. Which of the following is optical illusion?

(1) Rainbow
(2) Earthshine
(3) Halo
(4) Mirage
353. (4) A mirage is a naturally occurring optical illusion or phenomenon in which light rays are bent due to refraction in layers of air of varying density. The image usually is upside down, enhancing the illusion that the sky image seen in the distance is really a water or oil puddle acting as a mirror.

(1) Inertia of motion
(2) Frictional force
(3) Moment of a force
(4) Principle of moments
354. (1) An athlete does so to build up forward momentum so that when he jumps he already has a forward motion that would be greater than that of a jump made from standing in one spot. He needs forward momentum to get a good long jump and the best way is to have a running start. In this way, he gets advantage in terms of inertia of motion which is the tendency of an object to resist a change in motion.

### 355. In sunlight a rose appears red. In green light, the same rose appears

(1) red
(2) black
(3) green
(4) yellow
355. (2) Any object which allows light to pass through it is known as a transparent object. The colour of any transparent object is the colour of the light transmitted by it. A red rose appears red in white light because it absorbs all colours except red. However, when seen in green light, it looks black because the red colour of the rose is absorbed by the green light.

### 356. The sparkling of a diamond is due to

(1) total internal reflection of light
(2) interference of light
(3) polarisation of light
(4) refraction of light
356. (1) Diamonds sparkle because of the total internal reflection of light. Diamonds have a very high refractive index, meaning they slow light down much more than glass; and if cut in the right manner, the angles of incidence can be made so that light seems to get ‘trapped’ within the diamond giving it it’s sparkly appearance.

### 357. Ocean currents are an example of

(1) convection
(2) conduction
(3) insulation
357. (1) Heat is transferred by convection in numerous examples of naturally occurring fluid flow, such as: wind, oceanic currents, and movements within the Earth’s atmosphere. Winds and ocean currents are examples of convection currents. Convection serves to transfer heat from the surplus to deficit heat zones and set the oceanic circulation in motion.

### 358. If a copper wire is increased to double its length, its resistance will become

(1) four times
(2) one–fourth
(3) double
(4) half
358. (3) There is a direct relationship between the amount of resistance encountered by charge and the length of wire it must traverse. After all, if resistance occurs as the result of collisions between charge carriers and the atoms of the wire, then there is likely to be more collisions in a longer wire. An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area.

### 359. In a diesel engine the high temperature needed to ignite the fuel is achieved by

(1) using heat from exhaust
(2) the battery
(3) compressing air in the cylinders
(4) an electrical spark
359. (3) Diesel engines use the heat of compressed air to ignite the fuel (intakes air, compresses it, then injects fuel). Diesel engines need high compression ratios to generate the high temperatures required for fuel auto ignition.

### 360. Waves that are required for long distance wireless communication are

(1) Infrared rays
(2) Ultraviolet rays