FC-for-IAS-Prelims-2018-science-Day-37
70 Days WAR Plan

DAY#37 Static Flash Cards General Science [70 Days WAR Plan]

Density of Substances; Centrifugation Principle; Friction and Ball Bearings; Conduction; Altitudes and Atmospheric Pressure; Temperature and Heat; Total Internal Reflection; Refraction through Curved Surface; Angstrom;
By IT's Core Team
April 27, 2019

 

 

 

Angstrom is the unit to measure Pressure, Wavelength or Highspeed? 

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Answer: 

  • Angstrom is the unit to measure wavelength.

Enrich Your Learning:

Highspeed: 

  • The ratio of the speed of the aircraft to the speed of sound in the gas determines the magnitude of many of the compressibility effects. Because of the importance of this speed ratio, aerodynamicists have designated it with a special parameter called the Mach number in honor of Ernst Mach, a late 19th century physicist who studied gas dynamics. The Mach number M allows us to define flight regimes in which compressibility effects vary.

Wavelength:

  • The wavelength, λ, of a wave is the distance from any point on one wave to the same point on the next wave along. The unit for wavelength is the angstrom.

Speed:

  • Speed and velocity are both measured using the same units. The SI unit of distance and displacement is the meter. The SI unit of time is the second. The SI unit of speed and velocity is the ratio of two — the meter per second.

Pressure:

  • The pascal, symboled as Pa is the SI derived unit of pressure used to quantify internal pressure, stress, Young’s modulus and ultimate tensile strength. It is defined as one newton per square metre.

Energy:

  • The joule symbolized as J, is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre.

 

 

 

If a ray of light from the object appears to diverge from the principal focus located on the same side of the lens, then through which does the ray pass through after refraction? Concave lens or Convex lens?

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Answer:

  • If a ray of light from the object appears to diverge from the principal focus located on the same side of the lens, then it should pass through concave lens after refraction.

Enrich Your Learning: 

Refraction through Curved Surface:

A lens is a portion of a transparent refracting medium bounded by two spherical surfaces. Because the lenses are made from spheres, they are called as spherical lenses. They are mainly of two types :

  1. Convex lens
  2. Concave lens

Convex lens:

  • A convex lens is thick in middle and thin at the rim. It makes the parallel rays of light to converge and come to a point. Hence, it is also called a converging lens.

Concave lens:

  • A concave lens is thin in the middle and thick at rim. It makes the parallel rays of light to spread from a point. Hence it is also called a diverging lens.
  • The point at which the incident rays parallel to principal axis will converge upon after refraction in a convex lens is called its principal focus. Where as in a concave lens the point from where incident rays parallel to the principal axis of the lens appear to be coming, is called as its principal focus (F).
  • A ray of light from the object, parallel to the principal axis, after refraction from a convex lens, passes through the principal focus on the other side of the lens. In case of a concave lens, the ray appears to diverge from the principal focus located on the same side of the lens.
  • This is the reason why air bubble in water would act as a diverging lens as the index of refraction of air is less than that of water.
  • The ability of a medium to refract light is also expressed in terms of its optical density. Optical density has a definite connotation. It is not the same as mass density.
  • A ray of light travelling from a rarer medium to a denser medium slows down and bends towards the normal. When it travels from a denser medium to a rarer medium, it speeds up and bends away from the normal.

 

 

 

 

 

Optical fibres are fabricated such that light reflected at one side of inner surface strikes the other at an angle smaller than the critical angle. Do you agree?

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Answer:

  • Optical fibres are fabricated such that light reflected at one side of inner surface strikes the other at an angle larger than the critical angle.

Enrich Your Learning: 

Total Internal Reflection:

  • When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection.
  • When light gets reflected by a surface, normally some fraction of it gets transmitted. The reflected ray, therefore, is always less intense than the incident ray, howsoever smooth the reflecting surface may be. In total internal reflection, on the other hand, no transmission of light takes place.
  • All optical phenomena can be demonstrated very easily with the use of a laser torch or pointer, which is easily available nowadays.
  • Now-a-days optical fibres are extensively used for transmitting audio and video signals through long distances. Optical fibres too make use of the phenomenon of total internal reflection.
  • When a signal in the form of light is directed at one end of the fibre at a suitable angle, it undergoes repeated total internal reflections along the length of the fibre and finally comes out at the other end.
  • Since light undergoes total internal reflection at each stage, there is no appreciable loss in the intensity of the light signal. Optical fibres are fabricated such that light reflected at one side of inner surface strikes the other at an angle larger than the critical angle. Even if the fibre is bent, light can easily travel along its length. Thus, an optical fibre can be used to act as an optical pipe.
  • A bundle of optical fibres can be put to several uses. Optical fibres are extensively used for transmitting and receiving electrical signals which are converted to light by suitable transducers.
  • Obviously, optical fibres can also be used for transmission of optical signals.
  • For example, these are used as a ‘light pipe’ to facilitate visual examination of internal organs like esophagus, stomach and intestines. Decorative lamp with fine plastic fibres with their free ends forming a fountain like structure. The other end of the fibres is fixed over an electric lamp. When the lamp is switched on, the light travels from the bottom of each fibre and appears at the tip of its free end as a dot of light. The fibres in such decorative lamps are optical fibres.
  • The main requirement in fabricating optical fibres is that there should be very little absorption of light as it travels for long distances inside them. This has been achieved by purification and special preparation of materials such as quartz.
  • In silica glass fibres, it is possible to transmit more than 95% of the light over a fibre length of 1 km.

 

 

 

What does the ice point and steam point symbolize?

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Answer:

  • The ice point and the steam point of water are two convenient fixed points and are known as the freezing and boiling points. These two points are the temperatures at which pure water freezes and boils under standard pressure.

Enrich Your Learning:

Temperature and Heat:

  • Temperature is a relative measure, or indication of hotness or coldness. A hot utensil is said to have a high temperature, and ice cube to have a low temperature. An object that has a higher temperature than another object is said to be hotter.
  • A glass of ice-cold water left on a table on a hot summer day eventually warms up whereas a cup of hot tea on the same table cools down. It means that when the temperature of body, icecold water or hot tea in this case, and its surrounding medium are different, heat transfer takes place between the system and the surrounding medium, until the body and the surrounding medium are at the same temperature.
  • Heat is the form of energy transferred between two (or more) systems or a system and its surroundings by virtue of temperature difference.
  • Taking and example, the ice point and the steam point of water are two convenient fixed points and are known as the freezing and boiling points. These two points are the temperatures at which pure water freezes and boils under standard pressure.
  • Steam at 100°C and boiling water at 100°C contain same amount of heat.
  • The amount of heat per unit mass transferred during change of state of the substance is called latent heat of the substance for the process.
  • For example, if heat is added to a given quantity of ice at –10 °C, the temperature of ice increases until it reaches its melting point (0 °C). At this temperature, the addition of more heat does not increase the temperature but causes the ice to melt, or changes its state. Once the entire ice melts, adding more heat will cause the temperature of the water to rise.
  • A similar situation occurs during liquid gas change of state at the boiling point. Adding more heat to boiling water causes vaporisation, without increase in temperature.

 

 

 

Does the air pressure always decrease at the same rate with increase in altitude? Yes or No.

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Answer: 

  • No, air pressure decreases with increase in altitude but it does not always decrease at the same rate.

Enrich Your Learning: 

Altitudes and Atmospheric Pressure:

  • Altitudes means the height above the average sea level. The atmosphere becomes less dense and we feel breathlessness as we go higher from the earth surface and thus the temperature also decreases with the height.
  • Air pressure decreases with increase in altitude but it does not always decrease at the same rate. Dense components of atmosphere are found in its lowest parts near the mean sea level.
  • Temperature of the air, amount of water vapour present in the air and gravitational pull of the earth determine the air pressure of a given place and at a given time. Since these factors are variable with change in height, there is a variation in the rate of decrease in air pressure with increase in altitude.
  • The normal rate of decrease in air pressure is 34 millibars per every 300 metres increase in altitude.
  • The effects of low pressure are more clearly experienced by the people living in the hilly areas as compared to those who live in plains.
  • In high mountainous areas rice takes more time to cook because low pressure reduces the boiling point of water.
  • Breathing problem such as faintness and nose bleedings are also faced by many trekkers from outside in such areas because of low pressure conditions in which the air is thin and it has low amount of oxygen content.

 

 

 

How does cooking equipment having good and bad conductors of heat used together?

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Answer:

  • In cooking, copper cooking pots are used as they are good conductor of heat while wooden large spoon is used and even sometimes kept in the hot cooking copper pot along with working flame because of it being bad conductor of heat. Here the theory of transfer of heat work along with individual being different conductors of heat with different density.

Enrich Your Learning:

Conduction:

Conduction is the mechanism of transfer of heat between two adjacent parts of a body because of their temperature difference.

  • Heat conduction may be described quantitatively as the time rate of heat flow in a material for a given temperature difference.
  • Comparing the relatively large thermal conductivities of the good thermal conductors, the metals, with the relatively small thermal conductivities of some good thermal insulators, such as wood and glass wool.
  • Some cooking pots have copper coating on the bottom. Being a good conductor of heat, copper promotes the distribution of heat over the bottom of a pot for uniform cooking.
  • In an experiment heating up to same temperature copper piece is found hotter than in relation to glass piece. The reason is that copper being a metal is a good conductor of heat and electricity while glass on the other hand is a poor conductor of heat.
  • Along with this even the density differs from each other.
  • The density of copper is 8.92 gm/cm3 and of glass is 2.6 gm/cm3.

 

 

 

What role does ball bearing play in bicycle? Friction or Traction?

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Answer:

  • Ball bearing in bicycle plays the role of frictional.

Enrich Your Learning:

About Friction and Ball Bearings:

  • Due to friction, a lot of energy is wasted in the form of heat that causes wear and tear of the moving parts of a machine.
  • Friction also reduces efficiency of the machines as considerable amount of energy is wasted in overcoming friction. However, the efficiency of a machine can be increased by putting a suitable lubricant between its moving parts.
  • In most of the machines, to reduce friction ball bearings are used between the moving parts. By using the ball bearing the sliding friction is replaced by rolling friction.
  • As the rolling friction is less than the sliding friction, therefore, the friction between the moving parts is reduced.
  • Ball bearings are used to reduce friction and friction is directly proportionate to effective surface area. Thus if actual surface area is reduced then friction will also reduce.

 

 

 

Clouds are able to float due to lower pressure and velocity compared to air. Is this statement correct?

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Answer:

  • Clouds are able to float in air due to lower density compared to air.

 Enrich Your Learning:

About Density:

  • Since air has weight it must also have density, which is the weight for a chosen volume, such as a cubic inch or cubic meter. If clouds are made up of particles, then they must have weight and density.
  • The key to why clouds float is that the density of the same volume of cloud material is less than the density of the same amount of dry air.
  • Just as oil floats on water because it is less dense, clouds float on air because the moist air in clouds is less dense than dry air. This concept of density applies even to the floating of ship on water.

 

 

 

The density of mercury is greater than gold while the density of steel is lower than mercury. True or False?

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Answer:

  • The density of mercury is lower than gold. Density of mercury is 13.534 g/cm3 while density of gold is 19.30 g/cm3.

 Enrich Your Learning:

About Density of Substances:

  • The mass of a unit volume of a substance is called its density.
  • The density is thus a measure of its heaviness; more the density, heavier is the substance.
  • The density of air decreases with height.
  • The density of water at 4oC (277 K) is 1.0 × 103 kg m–3.
  • The relative density of a substance is the ratio of its density to the density of water at 4oC.
  • It is a dimensionless positive scalar quantity.
  • For example, the relative density of aluminum is 2.7. Its density is 2.7 × 103 kg m–3.

The following are examples of density of substances:

  • Density of the atmosphere at sea level is 1.29 kg/m3.
  • Density of oil is 1.5 ×103 kg m-3, density of copper is 8.9 × 103 kg m-3.
  • Density of mercury = 13.6 × 103 kg m–3.
  • Density of gold is 19.30 g/cm3.
  • Density of ultra pure liquid mercury is 13.534 g/cm3
  • Density of steel is 7.80 g/cm3.

 

 

 

Working of washing machine and separation of butter from curd is based on which principle: Centripetal principle OR Centrifugal principle?

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Answer:

  • Both the activities of working of washing machine and separation of butter from curd is based on centrifugal principle.

Enrich Your Learning:

About Centrifugation Principle:

  • A centrifuge is the equipment generally driven by an electric motor that puts an object to rotate around fixed axis, and a perpendicular force is applied to axis. The particles get separated according to their size, shape, density, viscosity of the medium and rotor speed.
  • The centrifuge involves principle of sedimentation, where the acceleration at centripetal force causes denser substances to separate out along the radial direction at the bottom of the tube. By the same concept lighter objects will tend to move to the top of the tube; in the rotating picture, move to the center.
  • In a solution, particles whose density is higher than that of the solvent sink (sediment), and particles that are lighter than it float to the top. The greater the difference in density, the faster they move.
  • If there is no difference in density (isopycnic conditions), the particles stay steady. To take advantage of even tiny differences in density to separate various particles in a solution, gravity can be replaced with the much more powerful “centrifugal force” provided by a centrifuge.
  • Some of the examples where this principle is applied are: fine mud particles suspended in water utilizes the principle of centrifugation while butter can be separated from curd by centrifugation. Working of washing machine also works under centrifugal principle.
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