# KPK Board 10th Class Physics Ch 3 Geometrical Optical Short Questions Answers

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We provided 10th class Physics short questions answers on this page of all KPK boards. Students of KPK boards can prepare the Physics subject for annual examinations.

In this List we have included all KPK boards and both Arts and Science students. These Boards students can prepare their exam easily with these short question answer section

Malakand Board 10th classes short questions Answer

Mardan Board 10th classes short questions Answer

Peshawar Board 10th classes short questions Answer

Swat Board 10th classes short questions Answer

Dera Ismail Khan Board 10th classes short questions Answer

Kohat Board 10th classes short questions Answer

Bannu Board 10th classes short questions Answer

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Which type of lens would you use to start fire from light of sum, concave or convex? At what distance from the lens should the paper be held for best result?

Ans .      we will use a convex lens ( converging lens) to start fire from light of sun. The paper should be held at the focus ( F) as all rays converges here as shown in the figure.

Explanation:       A convex lens, converges all rays falling on it to a single point due to which paper burns from the heat of sun. Moreover , as shown in the figure, all the rays focused on the focal length. That is why if we held a piece of paper on the focus, it will burn soon as compared to other position.

If a concave mirror produces a real images, is the image be necessarily inverted? Explain?

Ans.       Yes,  the image be necessarily invented if a concave mirror produces a real images.

Explanation:       A concave mirror produces real image when the object is placed beyond C, on C, and between C and F. In all these cases the images are real and inverted. How ever, if the object is placed between pole P  and focus F, the image formed will be upright but that will be a virtual image and not real. That is why it is said that a real image formed by a concave lens will always inverted.

Are rear – view mirrors in cars concave or convex?

Ans.       The rear  – view mirrors in cars are always convex in nature.

Explanation:       A convex mirror minimizes the image and it is always upright due to which it helps the driver  to see the cars upright that are coming from back. Objects in the convex mirror are closer then they appear because the convex mirror produces an image that is reduced in size, which makes the object look as if it  is farther away. Therefore, the external rear – view side s mirror on most cars carry the phrase “ objects in the mirror are closer then they appear” . Sometimes a small plan mirror is held  with the convex mirror in order to get the idea about the closeness of the cars from behind.

A magician during a show makes a glass lens with n = 1.47 disappear in a trough of liquid. What is the refractive index of the liquid? Could the liquid be water?

Ans.       The refractive index of the liquid should be equal to the refractive index of glass lens ( i.e. 1.47 ) for it to disappear in the liquid.  The liquid cannot be water as its refractive index is 1.33 which much less that of the glass lens. It can be glycerin or turpentine; both or “ clear” liquid with their refractive index equal to 1.47.

Suppose that you were handed a lens and a ruler and told to determine the focal length of the lens, how would you proceed?

Ans.       We can easily find the focal length of a lens by falling sun rays parallel on the lens and finding  the point where all rays are concentrated, which will be the principal focus of the lens.

Explanation.       As show in above figure all the rays are concentrated on one point which is called focus ( focal point) of the lens. We can easily measure the length of which will be focal length of the given lens.

Can we achieve total internal reflection when light travels from optically rare medium to optically dense medium?

Ans.       No, we cannot achieve total internal reflection when light travels from optically rare medium to optically dense medium.

Explanation:       One of the two fundamental conditions for total internal refraction is “ the light must travel from an optically dance medium into an optically rare medium ( e.g. from water to air)”.which means that total internal reflection cannot be achieved when light travels from optically rare medium to optically dense medium ( e.g. from air to water)

Will a near sighted person who wears corrective lenses in her glass, be able to see clearly under water when wearing those glasses?

Ans.       She will not see clearly under water when wearing those glasses because of the different refractive index of water than air.

Explanation:       water has a refractive index of 1.332 which is much greater than that of air ( 1.002 ). This high refractive index of water affects the refraction of light rays due to which she ( or any – glasses having corrective lenses.

When you use a simple magnifying glass, does it matter whether you hold the object, to be examined , closer to the lens than its focal length or farther away? Explain.

Ans.       Yes, it matters whether we hold the object, to be examined, closer to the lens then its focal length or further away.

Explanation:       it is the principle of a magnifying glass that we should place an object closer than its focal length in order to get a magnified object. So, when we hold an object to a magnifying glass closer than its focal length, the image will be magnified more.

In blind turns on hilly roads, mirror are used to help drivers. Are these mirrors plane, concave or convex mirror? Explain.

Ans.       Convex mirror are used in turns on hilly roads to help drivers to see vehicles coming from the other side.

Explanation:       A convex mirror bends light as it reflects the light, and the father away a point is from the centre, the more the light is bent. As a result, an image formed in a convex mirror is smaller than an image in a plane ( flat) mirror. Because the image is smaller, more image can fit onto the mirror, so a convex mirror provides a larger field of view than a plane mirror.

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