Science (English Medium) कक्षा १२ - CBSE Important Questions

Write the structures of the main products of the following reactions:

Define the following with an example

Denatured protein

Write the product when D-glucose reacts with conc. HNO₃.

Write one difference between α-helix and β-pleated structures of proteins.

Shyam went to a grocery shop to purchase some food items. The shopkeeper packed all the items in polythene bags and gave them to Shyam. But Shyam refused to accept the polythene bags and asked the shopkeeper to pack the items in paper bags. He informed the shopkeeper about the heavy penalty imposed by the government for using polythene bags. The shopkeeper promised that he would use paper bags in future in place of polythene bags.

1) Write the values (at least two) shown by Shyam.

2) Write one structural difference between low-density polyethene and high-density polyethene.

3) Why did Shyam refuse to accept the items in polythene bags?

4) What is a biodegradable polymer? Give an example.

What is tincture of iodine? What is its use?

Among the following, which one acts as a food preservative?

Aspartame, Aspirin, Sodium Benzoate, Paracetamol

Read the passage given below :

1. To ensure its perpetuity, the ground is well held by the panther both in space and in time. It enjoys a much wider distribution over the globe than its bigger cousins and procreates sufficiently profusely to ensure its continuity for all time to come.

Read the passage given below:

People tend to amass possessions, sometimes without being aware of doing so. They can have a delightful surprise when they find something useful which they did not know they owned. Those who never have to change house become indiscriminate collectors of what can only be described as clutter. They leave unwanted objects in drawers, cupboards, and attics for years in the belief that they may one day need them. Old people also accumulate belongings for two other reasons, lack of physical and mental energy, and sentiment. Things owned for a long time are full of associations with the past, perhaps with the relatives who are dead, and so they gradually acquire a sentimental value.

Some things are collected deliberately in an attempt to avoid wastage. Among these are string and brown paper, kept by thrifty people when a parcel has been opened. Collecting small items can be mania. A lady cuts out from newspaper sketches of model clothes that she would like to buy if she had money. As she is not rich, the chances are that she will never be able to afford such purchases. It is a harmless habit, but it litters up her desk.

Collecting as a serious hobby is quite different and has many advantages. It provides relaxation for leisure hours, as just looking at one’s treasure is always a joy. One doesn’t have to go out for amusement as the collection is housed at home. Whatever it consists of - stamps, records, first editions of books, china – there is always something to do in connection with it, from finding the right place for the latest addition to verifying facts in reference books. This hobby educates one not only in the chosen subject but also in general matters which have some bearing on it.

There are other benefits also. One gets to meet like-minded collectors to get advice, compare notes, exchange articles, to show off one’s latest find. So one’s circle of friends grows. Soon the hobby leads to traveling, perhaps a meeting in another town, possibly a trip abroad in search of a rare specimen, for collectors are not confined to one country. Over the years one may well become an authority on one’s hobby and will probably be asked to give informal talks to little gatherings and then, if successful, to larger audiences.

(a) On the basis of your understanding of the above passage make notes on it using headings and sub-headings. Use recognizable abbreviations (wherever necessary-minimum four) and a format you consider suitable. Also, supply an appropriate title to it.

(b) Write a summary of the passage in about 80 words.

Define electric flux.

Four point charges Q, q, Q and q are placed at the corners of a square of side 'a' as shown in the figure.

Find the

1) resultant electric force on a charge Q, and

2) potential energy of this system.

A 10 V cell of negligible internal resistance is connected in parallel across a battery of emf 200 V and internal resistance 38 Ω as shown in the figure. Find the value of current in the circuit.

State Ampere’s circuital law.

The susceptibility of a magnetic material is 0·9853. Identify the type of magnetic material. Draw the modification of the field pattern on keeping a piece of this material in a uniform magnetic field.

The teachers of Geeta’s school took the students on a study trip to a power generating station, located nearly 200 km away from the city. The teacher explained that electrical energy is transmitted over such a long distance to their city, in the form of alternating current (ac) raised to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices. As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how the ac is converted to a higher or lower voltage.

1) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.

2) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.

3) Write two values each shown by the teachers and Geeta.

Name the electromagnetic radiations used for (a) water purification, and (b) eye surgery.

The figure shows a ray of light falling normally on the face AB of an equilateral glass prism having refractive index`3/2`, placed in water of refractive index `4/3`.Will this ray suffer total internal reflection on striking the face AC? Justify your answer.

When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why?

State Huygen’s principle.

If one of two identical slits producing interference in Young’s experiment is covered with glass, so that the light intensity passing through it is reduced to 50%, find the ratio of the maximum and minimum intensity of the fringe in the interference pattern.