Science (English Medium) इयत्ता १२ - CBSE Important Questions

Show graphically an audio signal, a carrier wave and an amplitude modulated wave

A carrier wave of peak voltage 15 V is used to transmit a message signal. Find the peak voltage of the modulating signal in order to have a modulation index of 60%

How do you convert the following:

Aniline to phenol

How do you convert the Ethanal to Propanone

When concentrated sulphuric acid was added to an unknown salt present in a test tube a brown gas (A) was evolved. This gas intensified when copper turnings were added to this test tube. On cooling, the gas (A) changed into a colourless solid (B).

1) Identify (A) and (B).

2) Write the structures of (A) and (B).

3) Why does gas (A) change to solid on cooling?

Arrange the following in the decreasing order of their reducing character :

HF, HCl, HBr, HI

Account for the following:

pK_a value of 4-nitrobenzoic acid is lower than that of benzoic acid.

Give a simple chemical test to distinguish between Aniline and N, N-dimethylaniline

In a potentiometer arrangement for determining the emf of a cell, the balance point of the cell in open circuit is 350 cm. When a resistance of 9 Ω is used in the external circuit of the cell, the balance point shifts to 300 cm. Determine the internal resistance of the cell.

Using the concept of free electrons in a conductor, derive the expression for the conductivity of a wire in terms of number density and relaxation time. Hence obtain the relation between current density and the applied electric field E.

Write the underlying principle of a moving coil galvanometer.

Define mutual inductance.

What do you understand by the statement, "Electromagnetic waves transport momentum"?

Draw a diagram of the microscopic structure of human sperm. Label the following parts in it and write their functions:

1. Acrosome
2. Nucleus
3. Middle piece

Explain the effect on the characteristics of a river when urban sewage is discharged into it.

Name any two biodiversity hot spots in India.

What type of azeotrope is formed by positive deviation from Raoult’s law?

Define the following term:

Fuel cell

How would you account for the following: Transition metals form complex compounds.

Account for the following:

E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺.