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Science (English Medium) Class 12 - CBSE Important Questions

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

Appears in 9 question papers
Chapter: [15] Communication Systems
Concept: Need for Modulation and Demodulation

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%

Appears in 9 question papers
Chapter: [15] Communication Systems
Concept: Modulation and Its Necessity

How do you convert the following:

Aniline to phenol

Appears in 8 question papers
Chapter: [7] Alcohols, Phenols and Ethers
Concept: Methods of Preparation of Phenols

How do you convert the Ethanal to Propanone

Appears in 8 question papers
Chapter: [7] Alcohols, Phenols and Ethers
Concept: Alcohols, Phenols and Ethers >> Nomenclature

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?

Appears in 8 question papers
Chapter: [7] P - Block Elements
Concept: Group 16 Elements - The Oxygen Family >> Sulphuric Acid

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

HF, HCl, HBr, HI

Appears in 8 question papers
Chapter: [7] P - Block Elements
Concept: Group 17 Elements - The Halogen Family

Account for the following:

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

Appears in 8 question papers
Chapter: [8] Aldehydes, Ketones and Carboxylic Acids
Concept: Physical Properties of Carboxylic Acids

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

Appears in 8 question papers
Chapter: [9] Amines
Concept: Concept of Amines >> Chemical Reactions of Amines - Carbylamine Reaction

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.

Appears in 8 question papers
Chapter: [3] Current Electricity
Concept: Cells, Emf, Internal Resistance

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.

Appears in 8 question papers
Chapter: [3] Current Electricity
Concept: Specific Resistance

Write the underlying principle of a moving coil galvanometer.

Appears in 8 question papers
Chapter: [4] Moving Charges and Magnetism
Concept: Moving Coil Galvanometer

Define mutual inductance.

Appears in 8 question papers
Chapter: [6] Electromagnetic Induction
Concept: Inductance >> Mutual Inductance

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

Appears in 8 question papers
Chapter: [8] Electromagnetic Waves
Concept: Electromagnetic Spectrum

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
Appears in 7 question papers
Chapter: [2] Human Reproduction
Concept: Gametogenesis

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

Appears in 7 question papers
Chapter: [13] Biodiversity and Its Conservation
Concept: Biodiversity

Name any two biodiversity hot spots in India.

Appears in 7 question papers
Chapter: [13] Biodiversity and Its Conservation
Concept: Loss of Biodiversity

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

Appears in 7 question papers
Chapter: [1] Solutions
Concept: Vapour Pressure of Liquid >> Vapour Pressure of Liquid- Liquid Solutions

Define the following term:

Fuel cell

Appears in 7 question papers
Chapter: [2] Electrochemistry
Concept: Electrochemical Cells

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

Appears in 7 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)

Account for the following:

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

Appears in 7 question papers
Chapter: [4] d-block and f-block Elements
Concept: General Properties of the Transition Elements (d-block)
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