Why Can’T We See Clearly Through Fog? - Physics


Why can’t we see clearly through fog?



During fog, the light coming from an object is partly deflected by the particles of the fog and does not reach the eye of the observer. Thus, the objects are not seen clearly.

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2015-2016 (March) All India Set 3 N


Give scientific reason : Danger signals are red in colour.

Fill in the blank:

Very fine particles mainly scatter ………… colored light.

Show with the help of a diagram, how unpolarised light from Sun gets linearly polarised by scattering.

In the meterbridge experimental set up, shown in the figure, the null point ‘D’ is obtained at a distance of 40 cm from end A of the meterbridge wire. If a resistance of 10Ω is connected in series with R1, null point is obtained at AD = 60 cm. Calculate the values of R1 and R2.

Describe briefly using a diagram how sunlight is polarised ?

Suppose you are inside the water in a swimming pool near an edge. A friends is standing on the edge. Do you find your friend taller or shorter than his usual height?

The image formed by a concave mirror

A thin lens is made with a material having refractive index
\[\mu = 1 \cdot 5\]. Both the side are convex. It is dipped in water \[\mu = 1 \cdot 33\]. It will behave like

A convex lens is made of a material having refractive index
\[1 \cdot 2\] Both the surfaces of the lens are convex. If it is dipped into water (μ = 1.33), it will behave like 

A concave mirror forms an image of 20 cm high object on a screen placed 5.0 m away from the mirror. The height of the image is 50 cm. Find the focal length of the mirror and the distance between the mirror and the object.


A 1 cm object is placed perpendicular to the principal axis of a convex mirror of focal length 7.5 cm. Find its distance from the mirror if the image formed is 0.6 cm in size.

A candle flame 1.6 cm high is imaged in a ball bearing of diameter 0.4 cm. If the ball bearing is 20 cm away from the flame, find the location and the height of the image.

A point source S is placed midway between two converging mirrors having equal focal length f as shown in figure. Find the values of d for which only one image is formed.

Locate the image of the point P as seen by the eye in the figure.

Light falls from glass (μ = 1.5) to air. Find the angle of incidence for which the angle of deviation is 90°.

A point source is placed at a depth h below the surface of water (refractive index = μ). (a) Show that light escapes through a circular area on the water surface with its centre directly above the point source. (b) Find the angle subtended by a radius of the area on the source.

A container contains water up to a height of 20 cm and there is a point source at the centre of the bottom of the container. A rubber ring of radius r floats centrally on the water. The ceiling of the room is 2.0 m above the water surface. (a) Find the radius of the shadow of the ring formed on the ceiling if r = 15 cm. (b) Find the maximum value of r for which the shadow of the ring is formed on the ceiling. Refractive index of water = 4/3.

A biconvex thick lens is constructed with glass (μ = 1.50). Each of the surfaces has a radius of 10 cm and the thickness at the middle is 5 cm. Locate the image of an object placed far away from the lens.

A paperweight in the form of a hemisphere of radius 3.0 cm is used to hold down a printed page. An observer looks at the page vertically through the paperweight. At what height above the page will the printed letters near the centre appear to the observer?

A beam of blue, green and yellow light passes through the the Earth's atmosphere. Name the colour which is scattered the most

Fill in the blank and rewrite the completed statement:

Very fine particles mainly scatter ______ light.

Explain: ‘How is a rainbow formed’?

Answer the following question in detail.

State the conditions under which a rainbow can be seen.

Answer the following question in detail.

Explain the formation of a primary rainbow. For which angular range with the horizontal is it visible?

Answer the following question in detail.

Explain the formation of a secondary rainbow. For which angular range with the horizontal is it visible?

Answer the following question in detail.

Is it possible to see primary and secondary rainbow simultaneously? Under what conditions?

Pick the wrong answer in the context with rainbow.

Rainbow is the phenomenon due to ______.

A plano-convex lens is made of material having refractive index 1.5. The radius of curvature of curved surface is 40 cm. The focal length of the lens is ____________ cm.

State any one difference between a primary rainbow and a secondary rainbow.

Explain the formation of primary and secondary rainbow.

A parallel beam of light of wavelength 5890 Å falls normally on a slit of width 0.2 mm. Find the distance between the first minima on the two sides of the central maximum of the diffraction pattern observed on a screen placed in the focal plane of a convex lens of focal length 50 cm. The lens is placed quite close to the slit.

The sky would appear red instead of blue if

A passenger in an aeroplane shall ______.


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