Class 10 Science - Chapter Light - Reflection and Refraction NCERT Solutions | Find the focal length of a lens of power

One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.

Find out, from Table 10.3, the medium having highest optical density. Also find the medium with lowest optical density.

     Table 10.3 Absolute refractive index of some material media

An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table 10.3.

Define 1 dioptre of power of a lens.

Find the focal length of a convex mirror whose radius of curvature is 32 cm.

The magnification produced by a plane mirror is +1. What does this mean?

We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

What is a good source of energy?

Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?

What are trophic levels? Give an example of a food chain and state the different trophic levels in it.

What changes can you make in your habits to become more environment-friendly?

What is the difference between a reflex action and walking?

What is the importance of DNA copying in reproduction?

If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Why should a magnesium ribbon be cleared before burning in air?

You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

How does the embryo get nourishment inside the mother’s body?

When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

What is the role of decomposers in the ecosystem?

The xylem in plants are responsible for

         (a) transport of water.                   (c) transport of amino acids.
         (b) transport of food.                     (d) transport of oxygen.

Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

What could be the reasons for adopting contraceptive methods?

Which of the following terms does not represent electrical power in a circuit?

(a) I²R          (b) IR²          (c) VI          (d) V²/R

Which of the following methods is suitable for preventing an iron frying pan from rusting?

(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) All of the above.

Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?