Science
Azim Taraporewala was a traveller and science enthusiast. During one of his travels he found himself on the edge of an island without any mode of communication. As he had read in many stories, he thought he would light a fire on the beach and travelling boats or ships could see that fire and come to give him a ride. He had run out of lighters and match-sticks but had a reading glass. Being a science enthusiast he knew some tricks and used that lens and a scrap of paper to light a fire, with the help of scorching rays from the sun.
(a) Which lens can be used by Azim to create the fire?
(b) What property of the lens helps Azim to create the fire?
Attempt either subpart C or D.
(c) List two more uses of this kind of lens.
OR
(d) Explain with reason the condition under which the lens can form both real as well as virtual images.
Refraction Lens
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Answer
(a) The lens used by Azim to create the fire is a convex lens.
(b) The convex lens has the property of converging parallel rays of sunlight to a single point known as the principal focus.
(c) Two more uses of a convex lens are:
- It is used in a magnifying glass to view small objects clearly by producing a magnified virtual image.
- It is used in optical instruments such as microscopes, cameras, projectors and telescopes to focus light and form images.
(d) A convex lens can form both real and virtual images depending on the position of the object:
- When the object is placed beyond the focus (F), the lens forms a real and inverted image on the opposite side of the lens.
- When the object is placed between the optical center (O) and the focus (F), the lens forms a virtual, erect and magnified image on the same side as the object.
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Related Questions
(a) Distinguish between ethanol and ethanoic acid experimentally.
Attempt either subpart B or C.
(b) Give the IUPAC name of the first member of Alkene which is formed by addition of conc. sulphuric acid to it. Illustrate the change with the help of a chemical equation.
OR
(c) “All combustion reactions are oxidation but all oxidation reactions are not combustion.” Justify.
Mohan and Rohit observed that shoots of a plant growing in shade bend towards the sunlight. Whereas, leaves of ‘Touch me not’ plant fold and droop soon after touching. They were curious to know how these movements occur in plants.
In order to help them understand the movements in the plants, answer the following questions:
Attempt either subpart A or B.
(a) What causes the bending of shoots in the plants as shown in figure A?
OR
(b) What causes the folding of the leaves in ‘Touch me not’ plant as shown in figure B?
(c) Compare the movement of growth of the pollen tube towards ovule with the movements shown in part A of the above figure.
(d) Compare the movement shown in figure B with the movement of body parts in the animals.
During a field trip, Mohan and Rohit observed that shoots of sunflower plants bend towards the sunlight. Whereas, leaves of ‘Touch me not’ plant begin to fold and droop soon after touching even during the day. They were curious to know how these movements occur in plants.
Attempt either subpart A or B.
(a) What causes the bending of shoots in the sunflower plants towards sunlight?
OR
(b) What causes the folding of the leaves in ‘Touch me not’ plants when touched by hand?
(c) Compare the movement of growth of the pollen tube towards ovule with the bending of shoots of sunflower plant towards sunlight.
(d) Compare the movement in folding of leaves of ‘Touch me not’ plants with the movement of body parts in the animals.
The below image is that of a reflecting telescope. Reflecting telescopes revolutionised our ways of looking into the sky. They employ mirrors to gather and focus light, rather than relying solely on lenses as in their refracting counterparts. These telescopes utilise precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where it forms an image for observation.
(a) What kind of image of the star is seen by the observer at the eyepiece?
(b) What kind of mirror is used in this reflecting telescope?
Attempt either subpart C or D.
(c) Explain with reason what kind of optical device (type of lens or mirror) that is used at the eyepiece.
OR
(d) What is the role of the plane mirror in the telescope?