Q1. The surface tension of water on adding detergent to it
(c) no change
(d) becomes zero
Ans: (b) 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.
Q2. In a refrigerator, the cooling system should always be
(a) at the top
(b) at the bottom
(c) at the middle
(d) can be anywhere
Ans: (b) 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.
Q3. Which of the following is optical illusion?
(a) Rainbow (b) Earthshine
(c) Halo (d) Mirage
Ans: (d) 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.
Q4. An athlete runs before long jump to get advantage on
(a) Inertia of motion
(b) Frictional force
(c) Moment of a force
(d) Principle of moments
Ans: (a) 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.
Q5. In sunlight a rose appears red.
In green light, the same rose appears
(a) red (b) black
(c) green (d) yellow
Ans: (b) 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.
Q6. The sparkling of a diamond is due to
(a) total internal reflection of light
(b) interference of light
(c) polarisation of light
(d) refraction of light
Ans: (a) 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.
Q7. Ocean currents are an example of
Ans: (a) 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.
Q8. If a copper wire is increased to double its length, its resistance will become
(a) four times (b) one–fourth
(c) double (d) half
Ans: (c) 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.
Q9. In a diesel engine the high temperature needed to ignite the fuel is achieved by
(a) using heat from exhaust
(b) the battery
(c) compressing air in the cylinders
(d) an electrical spark
Ans: (c) 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.
Q10. Waves that are required for long distance wireless communication are
(a) Infrared rays
(b) Ultraviolet rays
(c) Radio waves
Ans: (c) Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor. With radio waves distances can be short, such as a few metres for television remote control, or as far as thousands or even millions of kilometres for deep-space radio communications.
Q11. Rise of oil a wick is due to
(a) density of the oil
(b) viscosity of the oil
(c) surface tension of the oil
(d) pressure of the oil
Ans: (c) The phenomenon of rise or fall of liquid in a capillary tube is called capillarity. Oil rises through a wick due to capillarity. The narrow pores in the threads of a wick act like tiny capillaries, through which oil rises. Capillary action is the result of adhesion and surface tension.
Q12. The radiation initially produced in fluorescent tube is
Ans: (b) The primary radiation that is initially produced within a fluorescent lamp is analogous to that emitted by a low pressure mercury lamp. Fluorescent lamps produce UV radiation by ionizing low-pressure mercury vapour. A phosphorescent coating on the inside of the tubes absorbs the UV and converts it to visible light.
Q13. The ‘four stroke petrol engine’ is based on
Ans: (b) A four-stroke engine (also known as four-cycle) is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine’s crankshaft, and one single thermodynamic cycle. The earliest of these to be developed is the Otto cycle engine developed in 1876 by Nikolaus August Otto in Cologne, Germany, after the operation principle described by Alphonse Beau de Rochas in 1861.
Q14. It is dangerous to observe Solar eclipse with naked eyes because
(a) Infrared radiations from sun burn our retina
(b) Ultraviolet radiations from Sun burn our retina
(c) All radiations from sun initiate chemical reactions in eyes
(d) Cosmic rays reach eyes more during the eclipse
Ans: (b) The solar radiation that reaches the surface of Earth ranges from ultraviolet (UV) radiation at wavelengths longer than 290 nm to radio waves in the meter range. The tissues in the eye transmit a substantial part of the radiation between 380 and 1400 nm to the light-sensitive retina at the back of the eye. The concern over improper viewing of the Sun during an eclipse is for the development of “eclipse blindness” or retinal burns.
Q15. These waves cannot be transmitted through vacuum
Ans: (b) Sound is a mechanical wave that is created by vibrating objects and propagated through a medium from one location to another. Because mechanical waves rely on particle interaction in order to transport their energy, they cannot travel through regions of space that are void of particles. That is, mechanical waves cannot travel through a vacuum.
Q16. A gap is left between two rails of a railway track to accommodate……
of the metal.
(a) areal expansion
(b) volume expansion
(c) liner expansion
(d) apparent expansion
Ans: (c) The volume of materials changes depending on current temperature. Usually heat makes them expand, and cold leads them to contract. To a first approximation, the change in length measurements of an object (“linear dimension” as opposed to, e.g., volumetric dimension) due to thermal expansion is related to temperature change by a “linear expansion coefficient”. It is the fractional change in length per degree of temperature change.
Q17. If an ordinary glass tube and a glass capillary tube are both dipped in a beaker of water, water rises in
(b) only the glass tube
(c) only the capillary tube
Ans: (a) The rise or fall of liquid due to capillarity in a beaker of water depends upon the radius of the bore of the tube (s) which is/are dipped into it. The narrower the bore of the tube, the greater is the rise or fall of the liquid in the tube. So in this case, water will rise in both the glass tube and the glass capillary tube.
Q18. ‘Hydraulic brakes’ work on the principle of
(a) Pascal’s law
(b) Thomson’s law
(c) Newton’s law
(d) Bernoulli’s theorem
Ans: (a) Pascal’s law states that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container. According to Pascal’s principle, in a hydraulic system a pressure exerted on a piston produces an equal increase in pressure on another piston in the system. If the second piston has an area 10 times that of the first, the force on the second piston is 10 times greater, though the pressure is the same as that on the first piston. This effect is exemplified by the hydraulic press, based on Pascal’s principle, which is used in such applications as hydraulic brakes.
Q19. Stars in the sky appear to twinkle due to
(a) a series of refractions
(b) a series of reflections
(c) a surface tension phenomenon
(d) multiple diminishing brightness
Ans: (a) The movement of air (sometimes called turbulence) in the atmosphere of Earth causes a series of refractions which makes the starlight to get slightly bent as it travels from the distant star through the atmosphere down to us on the ground. This means that some of the light reaches us directly and some gets bent slightly away. To our eyes, this makes the star seem to twinkle.
Q20. A pilot has to release the bomb to hit a target
(a) right above the target
(b) beyond the target
(c) before the target
(d) None of these
Ans: (c) According to Newton’s first law, an object that is at rest will stay at rest unless an unbalanced force acts upon it and an object that is in motion will not change its velocity unless an unbalanced force acts upon it. So the bomb carries the inertia of the aircraft and so has to be launched before the target so that it can hit it on time. Assuming the plane continues to fly straight forward, the plane will be directly over the target when the bomb hits.
Q21. Parabolic mirros are used in
(a) Car headlights
(b) Driving mirrors
(c) Dentists mirros
(d) Shaving mirros
Ans: (a) A parabolic reflector (mirror) transforms an incoming plane wave traveling along the axis into a spherical wave converging toward the focus. Since the principles of reflection are reversible, parabolic reflectors can also be used to project energy of a source at its focus outward in a parallel beam, used in devices such as spotlights and car headlights.
Q22. Red is used as an emergency or danger signal as
(a) it is a striking colour
(b) its wavelength is the longest
(c) it is scattered
(d) it has very high energy
Ans: (b) 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.
Q23. Bats can sense obstacles because they produce
(a) supersonic sound waves
(b) ultrasonic sound waves
(c) infrasonic sound waves
(d) micro sound waves
Ans: (b) The reason that bats use ultrasound is because it has such a high frequency and it has a low diffraction or it bends less. They use this sound to do a couple of things like to catch their prey and also just to get around. The method of doing such tasks is called echolocation. They make a sound and wait for it to bounce back to hear it. If they hear it come faster in a particular area than the rest of the sounds then they know that something is near.
Q24. The resistance of the human body (dry condition) is of the order of
(a) 101 Ohm (b) 102Ohm
(c) 103 Ohm (d) 104 Ohm
Ans: (*) The level of current passing through the human body is directly related to the resistance of its path through the body. Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body’s resistance to 1,000 Ohms. (Source: The Guide to Photovoltaic System Installation by Gregory Fletcher)
Q25. The sharpness of a television image is termed as its
(a) Clarity (b) Colour
(c) Resolution(d) Graphics
Ans: (c) Resolution is an umbrella term that describes the detail an image holds. The term applies to raster digital images, film images, and other types of images. The display resolution of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed.
Q1. The surface tension of water on adding detergent to it