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ICSE-X-Physics

Previous Year Paper year:2018

with Solutions - page 2

#1-e [2]

#1-e-i
Why is the motion of a body moving with a constant speed around a
circular path said to be accelerated?
Ans : Although speed remains constant, its direction keeps on changing.
Hence, its velocity which is displacement in a specified direction
changes, and due to this, the movement in a circular path is said to be
accelerated.

#1-e-ii
Name the unit of physical quantity obtained by the formula ``\frac{2K}{V^2}``
Where K: kinetic energy, V: Linear velocity.
Ans : ``\frac{2K}{V^2}``
As we know ``K = \frac12 MV^2``, substituting K with this:
$$= \require{cancel} \frac{2 * \frac12 M\cancel{V^2}} {\cancel{V^2}} = M $$
M is mass and it's S.I. Unit is Kilogram (``\pu{kg}``)

#2

#2-a [2]
The power of a lens is - 5D.
(i) Find its focal length.
(ii) Name the type of lens.
Ans :
(i) The power of a lens is −5 D.
The power of a lens is defined as the reciprocal of its focal length in meters, or
$$ D = \frac1f$$ , where D is the power in diopters and f is the focal length in meters.
Focal length = ``\frac{100 cm}{−5} = \pu{−20 cm}``.
(ii) Since focal length is negative, the lens is a concave lens.

#2-b [2]
State the position of the object in front of a converging lens if:

#2-b-i
It produces a real and same size image of the object.
Ans : It produces a real and same size image of the object.
Thus, the object is at 2F1.

#2-b-ii
It is used as a magnifying lens.
Ans : It is used as a magnifying lens.
The object is between F1 and the optical centre.

#2-c [2]

#2-c-i
State the relation between the critical angle and the absolute refractive
index of a medium.
Ans : If the critical angle is C and ``\nu`` is the absolute refractive index, then
$$\pu{\sin C = \frac{1}{\nu} }$$

#2-c-ii
Which colour of light has a higher critical angle? Red light or Green light.
Ans : Red light has a higher critical angle because the refractive index of red
light is smaller than that of green light.

#2-d [2]

#2-d-i
Define scattering.
Ans : Scattering is the process of absorption and re-emission of light energy.

#2-d-ii
The smoke from a fire looks white. Which of the following statements is
true?
1. Molecules of the smoke are bigger than the wavelength of light.
2. Molecules of the smoke are smaller than the wavelength of light.
Ans : 1. Molecules of smoke are bigger than the wavelength of light -
True.
2. Molecules of smoke are smaller than the wavelength of light -
False.

#2-e [2]
The following diagram shows a 60°, 30°, 90° glass prism of critical angle
42°, Copy the diagram and complete the path of incident ray AB emerging
out of the prism marking the angle of incidence on each surface.

Ans :
The following diagram shows a 60°, 30°, 90° glass prism of critical angle 42°.