Chemical Reactions and Equations — Science STD 10 — Question

An object 2cm tall is placed on the axis of a convex lens of focal length 5cm at a distance of 10m from the optical centre of the lens. Find the nature, position and size of the image formed. Which case of image formation by convex lenses is illustrated by this example?

Draw a labelled ray diagram to show how a ray of light passes through a parallel sided glass block:

1. If it hits the glass block at 90° (that is, perpendicular to the glass block).
2. If it hits the glass block at an angle other than 90° (that is, obliquely to the glass block).

What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals?

Describe the working of a hydrogen bomb.

Why is atomic number considered to be a more appropriate parameter than atomic mass for the classification of elements in a periodic table? How does the metallic character of elements vary as we move (i) from left to right in a period, and (ii) top to bottom in a group in the modern periodic table? Give reasons to justify your answers.

What does the direction of thumb indicate in the right-hand thumb rule. In what way this rule is different from Fleming’s left-hand rule?

An object of size 7.0cm is placed at 27cm in front of a concave mirror of focal length 18cm. At what distance from the mirror should a screen be placed so that a sharp focussed image can be obtained? Find the size and nature of image.
[Hint. Find the value of image distance (v) first. The screen should be placed from the mirror at a distance equal to image distance.]

The atomic number of three elements A, B and C are 11, 14 and 17 respectively.
State the group to which these elements belong in the modern periodic table.

Explain giving one example, how highly reactive metals (which are high up in the reactivity series) are extracted.

The surface of water in a lake appears green due to a layer of tiny free-floating organisms X on its surface. The lake water also contains organisms like water beetle, fish and tadpole. The sun shines over the lake water and provides energy for the functioning of this lake ecosystem.

1. What could organisms X be?
2. Write a food chain comprising of all the four organisms mentioned.
3. What is the general name of the food chains like the one written above?
4. Name (i) secondary consumer (ii) producer (iii) tertiary consumer, and (iv) primary consumer, in the above food chain.
5. If the tertiary consumer gets 0.2 J of energy from the secondary consumer, then how much energy was radiated by the sun to the producer?