Q.1 The working principle of a washing machine is:
(a) centrifugation (b) dialysis
(c) reverse osmosis (d) diffusion
Q.2 When the same note is played on a sitar and a flute, the sound produced can be distinguished from each other because of the difference in
(a) pitch, loudness and quality
(b) pitch and loudness
(c) quality only
(d) loudness only
Q.3 Who among the following anticipated Newton by declaring that all things gravitate to the earth ?
(a) Aryabhatta (b) Varahamihira
(c) Buddhagupta (d) Brahmagupta
Q.4 Optical fibre works on the principle of :
(a) total internal reflection
Q.5 Suppose a rocketship is receding from the earth at a speed of 2/10 th the velocity of light. A light in the rocketship appears blue to the passengers on the ship. What colour would it appear to an observer on the earth ?
(a) Blue (b) Orange
(c) Yellow (d) Yellow-orange
Q.6 Cryogenic engines find applications in:
(a) sub-marine propulsion
(b) frost-free refrigerators
(c) rocket technology
(d) researches in superconductivity
Q.7 The clouds float in the atmosphere because of low :
(a) temperature (b) velocity
(c) pressure (d) density
Q.8 Given below are two statements, one labelled as Assertion (A) and other labelled as Reason (R)
Assertion (A) : A diamond sparkles more than a glass imitation cut to the same shape.
Reason (R) : The refractive index of diamond is less than that of glass.
In context of the above two statements, which one of the following is correct ?
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true and R is not a correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Q.9 An air bubble in water will act like a
(a) convex mirror (b) convex lens
(c) concave mirror (d) cancave lens
Q.10 When a mirror is rotated by an angle 10, the reflected ray will rotate by :
(a) 0° (b) 0/2
(c) 0 (d) 20
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Answer Key With Explanation:
Washing machine works on the principle of centrifugation.
Musical sound can differ from each other with respect to the following three characteristics :
(1) Loudness (intensity)
(2) Pitch (shrillhkssi
(3) Quality (timber)
But quality (timber) is that characteristic of a musical sound which enables us to distinguish between two sounds even if they have the same pitch and loudness.
Brahmagupta anticipated Newton by declaring that all things gravitate to the earth.
Optical fibres works on the principle of total internal reflection. When light is incident at a small angle at one end, it gets refracted into the fibres (or strands) and gets incident on the interface of the fibres and the coating. The angle of incidence being greater than the critical angle. So, the light suffers the internal reflections again and again till the angle of incidence being greater than the critical angle for the fibre material.
In the air or vacuum to any observer, the velocity of light is same. Since, on rocket ship light appears blue to an observer so on earth the observer will see the same colour.
Cryogenic engines find applications in rocket technology.
When air rises, it is cooled by expansion. After dew point has reached cooling leads to condensation of water vapour in the atmosphere. Tiny droplets of water vapour which are too small to fall as raize or shower will be suspended in the air and float as clouds.
Explanation The refractive index of diamond is very high (approximately 2.47) while the refractive index for
the glass is 1.57. Therefore, the initial angle for the ray of light traveling form diamond to air is very low about 24°. The initial angle for the ray of light traveling from glass to air is 39°. Moreover the diamonds are usually cut with their faces in such a manner that once a ray of light enters into it, it suffers a large number of total internal reflections at various faces till the angle of incidence inside the diamond remains greater than the critical angle. In total internal reflection 100% of the light reflected back into the same medium. Hence, the object shines. That's why a diamond sparkles more than a glass imitation cut to the same shape.
For given incident ray, if a plane mirror is rotated through a certain angle, then the reflected ray rotates through twice of that angle . So if a mirror is rotated by an angle 10, the reflected ray will rotate by 20.