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Part 011 – Physics Previous Year Questions

Q1. ‘Mirage’ is an example of
(a) refraction of light only
(b) total internal, reflection of light only
(c) refraction and total internal reflection of light
(d) dispersion of light only
Ans: (c) A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or the sky. In contrast to a hallucination, a mirage is a real optical phenomenon which can be captured on camera, since light rays actually are refracted to form the false image at the observer’s location. As light passes from colder air across a sharp boundary to significantly warmer air, the light rays bend away from the direction of the temperature gradient. When light rays pass from hotter to cooler, they bend toward the direction of the gradient. If the air near the ground is warmer than that higher up, the light ray bends in a concave, upward trajectory. Once the rays reach the viewer’s eye, the visual cortex interprets it as if it traces back along a perfectly straight “line of sight”. This line is however at a tangent to the path the ray takes at the point it reaches the eye.

Q2. The phenomenon of light associated with the appear-ance of blue colour of the sky is

(a) Interference
(b) Reflection
(c) Refraction
(d) Scattering
Ans: (d) During daylight, the sky appears to be blue because air scatters blue sunlight more than it scatters red. At night, the sky appears to be a mostly dark surface or region scattered with stars. Except for light that comes directly from the sun, most of the light in the day sky is a result of scattering, which is dominated by a small-particle limit called Rayleigh scattering. The scattering due to molecule sized particles (as in air) is greater in the forward and backward directions than it is in the lateral direction. Scattering is significant for light at all visible wavelengths, but it is stronger at the shorter (bluer) end of the visible spectrum, meaning that that the scattered light is more blue than its source, the sun.

Q3. Lens is made up of

(a) Pyrex glass(b) Flint glass
(c) Ordinary glass
(d) Cobalt glass
Ans: (b) Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). A concave lens of flint glass is commonly combined with a convex lens of crown glass to produce an achromatic doublet lens because of their compensating optical properties, which reduces chromatic aberration (colour defects).

Q4. The time period of a pendulum when taken to the Moon would:

(a) remain the same
(b) decrease
(c) become zero
(d) increase
Ans: (d) Since the pendulum rate will increase with an increase in gravity, and local gravity varies with latitude and elevation on Earth, pendulum clocks must be readjusted to keep time after a move. For example, a pendulum clock moved from sea level to 4000 feet will lose 16 seconds per day. Even moving a clock to the top of a tall building will cause it to lose measurable time due to lower gravity. Time period of a pendulum taken to the moon will be longer than the period of the same pendulum on earth.

Q5. The atmospheric air is held to the Earth by :

(a) gravity (b) winds
(c) clouds
(d) rotation of the Earth
Ans: (a) The atmosphere is an ocean of air held in place by gravity, extending from the surface to an altitude of hundreds of kilometers, the edge of space. Energy from the sun heating the air and land surface to different degrees, drives atmospheric circulation. Patterns of circulation are also influenced by Earth’s rotation, latitude and the distribution of land, ocean and ice. Surface gravity, the force that holds down an atmosphere, differs significantly among the planets. For example, the large gravitational force of the giant planet Jupiter is able to retain light gases such as hydrogen and helium that escape from lower gravity objects.

Q6. The function of ball bearings in a wheel is :

(a) to increase friction
(b) to convert kinetic friction into rolling friction
(c) to convert static friction into kinetic friction
(d) just for convenience
Ans: (b) A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. In general, it’s main function is to convert kinetic friction into rolling friction. It achieves this by using at least two races to contain the balls and transmit the loads through the balls.

Q7. ‘Shock-absorbers’ are usually made of steel as it :

(a) is not brittle
(b) has lower elasticity
(c) has higher elasticity
(d) has no ductile property
Ans: (c) A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. Steel is an alloy made by combining iron and other elements, the most common of these being carbon. When carbon is used, its content in the steel is between 0.2% and 2.1% by weight, depending on the grade. Varying the amount of alloying elements and the form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the higher elasticity, hardness, ductility, and tensile strength of the resulting steel.

Q8. Among the following materials sound travels fastest in

(a) Steel (b) Air
(c) Vacuum (d) Water
Ans: (a) The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s). the speed of sound varies from substance to substance. Sound travels faster in liquids and nonporous solids than it does in air. It travels about 4.3 times as fast in water (1,484 m/s), and nearly 15 times as fast in iron (5,120 m/s), than in air at 20 degrees Celsius. Sound waves in solids are composed of compression waves (just as in gases and liquids), but also exhibit a different type of sound wave called a shear wave, which occurs only in solids.

Q9. Lambert’s law is related to

(a) Reflection
(b) Refraction
(c) Interference
(d) Illumination
Ans: (d) In optics, Lambert’s cosine law says that the radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle between the observer’s line of sight and the surface normal. The law is also known as the cosine emission law or Lambert’s emission law. A surface which obeys Lambert’s law is said to be Lambertian, and exhibits Lambertian reflectance. Such a surface has the same radiance when viewed from any angle. This means, for example, that to the human eye it has the same apparent brightness (or luminance).

Q10. One can distinguish a telescope from a microscope by observing

(a) length
(b) colour
(c) size of the lens
(d) length and size of the lens
Ans: (d) Telescope and Microscope are two scientific instruments that serve their purposes differently. One of the main differences between a telescope and a microscope is that a telescope is used to view things that are far whereas a microscope is used to view things that are very near. Another important difference between telescope and microscope is that the focal length or the distance from the focal point to the lens is different in these two scientific instruments. As a result of this the focal point in the case of a telescope may be at a far off place. On the other hand the focal point in the case of a microscope is just a fraction of an inch off. The difference in the diameter of the lens used in the two instruments also matter a lot when it comes to the difference between them. The lens diameter or the aperture is much larger in a telescope. This is to ensure that the aperture allows tiny amount of natural light at the focal point .On the other hand only artificial illumination is used in a microscope.

Q11. The sound produced by a bat is–

(a) audible (b) subsonic
(c) infrasonic (d) ultrasonic
Ans: (d) Although bats use echolocation to detect their prey, and find their way around in the dark, the sounds which they emit are ‘ultrasonic’, which is another way of saying they are beyond the range of normal human hearing. 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. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.

Q12. When a bar magnet is cut into two equal halves, the pole strength of each piece –

(a) becomes double
(b) becomes half
(c) becomes zero
(d) remains the same
Ans: (d) The poles remains same whether the magnet is cut into two equal half or more and also pole strength remains same but magnetic moment reduces due to decrease in the length of the magnet. If a bar magnet is suspended by a thread, it will come to rest in a position close to the north-south direction. The end of the magnetic toward the north is called north pole (N-pole) of the magnet and the other end the south pole (S-pole). The poles of a magnet cannot be separated. If a bar magnet is broken into two parts, each part will be a complete magnet with the poles at its ends. No matter how many times a magnet is broken; each piece will contain N-pole at one end and S-pole at the other.

Q13. A new technology which provides the ability to create an artificial world and have people interact with it is called :

(a) Televirtuality
(b) Virtual reality
(c) Alternate reality
(d) 3-D reality
Ans: (b) Virtual reality (VR) is a term that applies to computer-simulated environments that can simulate physical presence in places in the real world, as well as in imaginary worlds. Most current virtual reality environments are primarily visual experiences, displayed either on a computer screen or through special stereoscopic displays, but some simulations include additional sensory information, such as sound through speakers or headphones. Some advanced, haptic systems now include tactile information, generally known as force feedback, in medical and gaming applications.

Q14. Electrostatic precipitator is used to control –

(a) Air pollution
(b) Water pollution
(c) Solid waste
(d) Noise pollution
Ans: (a) An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream. In contrast to wet scrubbers which apply energy directly to the flowing fluid medium, an ESP applies energy only to the particulate matter being collected and therefore is very efficient in its consumption of energy (in the form of electricity).

Q15. The time period of a seconds pendulum is

(a) 1 second (b) 2 seconds
(c) 0•5 second(d) 1•5 seconds
Ans: (b) A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and one second for the return swing, a frequency of 1/2 Hz. At standard gravity its length is 0.994 m.

Q16. Lakes freeze in cold countries in winter, leaving the water underneath at

(a) 0°C (b) 0°F
(c) 4°C (d) 4°F
Ans: (c) Lake ice cover is seasonal and occurs where average daily temperature is below the freezing point. Once formed the lake ice thickens over the course of the winter as the temperature gets colder. The lakes thermal structure prepares for ice with 0 (zero) degrees Celsius water at the surface and denser 4 degrees Celsius at the bottom. Once meteorological conditions provide colder air, relative to warmer water, the water does not get colder – instead ice forms.

Q17. Which one of the following determines the sharpness of image in a camera ?

(a) The aperture
(b) The exposure time
(c) The focal length of the lens
(d) Size of the camera
Ans: (a) Image quality is a characteristic of an image that measures the perceived image degradation (typically, compared to an ideal or perfect image). Imaging systems may introduce some amounts of distortion or artifacts in the signal, so the quality assessment is an important problem. Sharpness determines the amount of detail an image can convey. System sharpness is affected by the lens (design and manufacturing quality, focal length, aperture, and distance from the image center) and sensor (pixel count and anti-aliasing filter).

Q18. In MRI machine, which one of the following is used?

(a) Sound wave
(b) ‘X’-ray
(c) Ultra-sound wave
(d) Magnetic wave
Ans: (d) Magnetic resonance imaging (MRI), nuclear magnetic resonance imaging (NMRI), or magnetic resonance tomography (MRT) is a medical imaging technique used in radiology to visualize internal structures of the body in detail. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body. An MRI scanner is a device in which the patient lies within a large, powerful magnet where the magnetic field is used to align the magnetization of some atomic nuclei in the body, and radio frequency fields to systematically alter the alignment of this magnetization. This causes the nuclei to produce a rotating magnetic field detectable by the scanner—and this information is recorded to construct an image of the scanned area of the body.

Q19. For a person having hypermetropia, the near point is

(a) greater than 25 cm
(b) greater than 50 cm
(c) less than 25 cm
(d) infinity
Ans: (a) For a hyper-metropic eye ,the near points shift away from the eye i.e. farther away from the normal near point (25cm). In a hypermetropic eye, the light is not bent sufficiently so that it focuses at a point behind the retina. Here a person sees well for distance but near vision is difficult and causes strain. Hence hypermetropic people are called long-sighted. To correct the hypermetropic eye, a plus lens is required so that the light can now focus on the retina.

Q20. Amount of water vapour in the atmosphere is measured in terms of

(a) Humidity
(b) Droplets
(c) Smog
(d) All of the above
Ans: (a) Humidity is the amount of water vapor in the air. Water vapor is the gas phase of water and is invisible. Humidity indicates the likelihood of precipitation, dew, or fog. Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table, used during summer weather. There are three main measurements of humidity: absolute, relative and specific.

Q21. Name the process of production of energy in the Sun

(a) Nuclear fission
(b) Radioactivity
(c) Nuclear fusion
(d) Ionization
Ans: (c) The source of the sun’s fuel is hydrogen and helium gases. Through a special chemical reaction, called nuclear fusion, the hydrogen gas is “burned” releasing an enormous amount of energy in the form of light and heat. In nuclear physics, nuclear fusion is a nuclear reaction in which two or more atomic nuclei join together, or “fuse”, to form a single heavier nucleus. During this process, matter is not conserved because some of the mass of the fusing nuclei is converted to energy which is released. Fusion is the process that powers active stars. The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy, while the fusion of nuclei heavier than iron absorbs energy. The opposite is true for the reverse process, nuclear fission.

Q22. A spherical ball made of steel when dropped in mercury container will

(a) sink in mercury
(b) will be on the surface of mercury
(c) will be partly immersed mercury
(d) will dissolve in mercury
Ans: (b) The density of steel usually ranges between 7.75 and 8.05 g/cm3 and the density of mercury is 13.534 g/cm3. Mercury is denser than steel this will mean that the buoyant force is large enough to float the steel ball. Different materials usually have different densities, so density is an important concept regarding buoyancy, purity and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but not the densest materials. Less dense fluids float on more dense fluids if they do not mix.

Q23. The sounds having a frequency of 20 Hertz to 20,000 Hertz are known as

(a) Audible sounds
(b) Ultrasonics
(c) Infrasonics
(d) Megasonics
Ans: (a) An audio frequency is characterized as a periodic vibration whose frequency is audible to the average human. It is the property of sound that most determines pitch and is measured in hertz (Hz).The generally accepted standard range of audible frequencies is 20 to 20,000 Hz, although the range of frequencies individuals hear is greatly influenced by environmental factors. Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough. Frequencies above 20,000 Hz can sometimes be sensed by young people.

Q24. Eclipses occur due to which optical phenomena?

(a) Reflection (b) Refraction
(c) Rectilinear propagation
(d) Diffraction
Ans: (c) An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. Rectilinear propagation is a wave property which states that waves propagate (move or spread out) in straight lines. This property applies to both transverse and longitudinal as well as an Electromagnetic wave. Even though a wave front may be bent (the waves created by a rock hitting a pond) the individual waves are moving in straight lines.

Q25. Pure water is bad conductor of electricity because it is

(a) feebly ionized
(b) not volatile
(c) a very good solvent
(d) a non-polar solvent
Ans: (a) Pure water is a covalent compound. It exists as simple discrete molecules and have a simple molecular structure. Hence, it does not exist as ions. Therefore, pure water cannot conduct electricity due to the absence of mobile ions and electrons. One instance that water can conduct electricity is when there are dissolved substance in it. Only then will water dissociate into hydrogen ions and hydroxide ions. The presence of mobile ions enables it to conduct electricity.

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