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PHYSICS [2 Mark Question Answer]

Light Energ · ICSE STD 8 (ICSE - English Medium). 13 questions.

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[2 Mark Question Answer]

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13 questions · timed · auto-graded

Question 12 Marks
What do you understand by refraction of light?
Answer
Refraction is the bending of light as it passes from one substance to another. Here the light ray passes from air to glass and back to air. The bending is caused by the differences in density between the two substance.
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Question 22 Marks
Name the kind of mirror used to obtain
$(a)$ a real and enlarged image
$(b)$ a virtual and enlarged image
$(c)$ a real and diminished image, and
$(d)$ a virtual and diminished image.
Answer
$a)$ Concave
$b)$ Concave
$c)$ Concave
$d)$ Convex
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Question 32 Marks
Out of air and glass, which is optically rarer? Give reason.
Answer
Air is $\text{RARER}$ as the speed of light in air is more than the speed of light in glass.
$3 \times 10^8 ms^{-1} > 2 \times 10^8 ms^{-1}$
speed of light in air $>$ speed of light in glass
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Question 42 Marks
State two uses of a convex mirror.
Answer
Two USES OF CONVEX MIRROR:
$1.$ It is used as a REARVIEW MIRROR.
$2.$ It is used as a VIGILANCE MIRROR
$3.$ It is used as a REFLECTOR IN STREET LAMPS
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Question 52 Marks
State two uses of a concave mirror.
Answer
Two uses of concave mirror are :
$1.$ Concave mirror is used as $\text{REFLECTOR}$ in headlights of cars and in searchlight. The source of light $($bulb$)$ is placed at the principal focus and the reflector forms a parallel beam of light.
$2.$ For doctors to examine throat, ear, nose and eyes, light is focused with the help of a concave mirror.
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Question 62 Marks
What is a real image? Name the mirror which can be used to obtain the real image of an object. What should be the position of the object relative to the mirror?
Answer
REAL IMAGE. “When rays of light after reflection or refraction actually meet at some other point” the image is real. Concave mirror.
Except between pole and focus, the image formed is $\text{REAL}$
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Question 72 Marks
The diagram $($figure$)$ given below shows two parallel rays $1$ and $2$ incident on $(a)$ a concave mirror, $(b)$ a convex mirror. Draw the reflected rays and mark the focus by the symbol $F$.
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Question 82 Marks
How is the focal length of a spherical mirror related to its radius
Answer
The distance from the pole to the focal point is called the focal length $(f)$. The focal length of a spherical mirror is then approximately half its radius of curvature.
Focal length $=$ Radius of curvature $/ 2$
Or $2 F = R$
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Question 92 Marks
How does the speed of light determine the optical density of a medium?
Answer
If the speed of light in a medium is less than the speed of light in air, means the $\text{MEDIUM}$ is $\text{DENSER}$ than air.
If the speed of light is more than the speed of light in $\text{AIR,}$ means the $\text{MEDIUM}$ is $\text{LESS DENSER}$ than air.
Speed of light is $1$ density of medium
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Question 102 Marks
State the two laws of reflection of light.
Answer
Laws of reflection :
$1.$ The incident ray, the reflected ray and the normal ray at the point of incidence, lie in the same plane.
$2.$ The angle of incidence i is equal to the angle of reflection $r$ i.e. $\angle i = \angle r$
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Question 112 Marks
What do you understand by the term spectrum? Name the various colours present in the spectrum of sunlight.
Answer
Spectrum is the band of colours obtained on a screen when white light passes through a prism and splits into its constituent colours. The colours of the spectrum are violet $(V)$, indigo $(1),$ blue $(B)$, green $(G)$, yellow $(Y)$, orange $(O)$, and red $(R).$
The order of the spectrum is $\text{VIBGYOR}.$
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Question 122 Marks
State the speed of light in $(a)$ air, $(b)$ water, and $(c)$ glass
Answer
Speed of light in
Air $ - 3 \times 10^8 ms^{-1}$ or $300000\  km / h$
Water $-2.25 \times 10^8 ms^{-1}$
Glass$ - 2 \times 10^8 ms^{-1}$
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Question 132 Marks
A ray of white light falls on a prism. Draw a ray diagram to show that the prism disperses the white light.
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[2 Mark Question Answer] - PHYSICS STD 8 Questions - Vidyadip