# Author: Dr. Vikas Jasrotia Question 2.8: What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy? https://www.youtube.com/watch?v=lCdbg6Dtw3I Question 2.8: What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy? Ans 2.8: Energy (E) of a photon = hν Energy (En) of ‘n’ photons = nhν ν = c/Λ n = EnΛ /hc Where, λ = wavelength of light = 4000 pm = 4000 ×10–12 m c = velocity of light in vacuum = 3 × 108 m/s h = Planck’s constant = 6.626 ×…

Question 2.7: Calculate the wavelength frequency and wave number of a light wave whose period is 2.0 × 10–10 s. https://www.youtube.com/watch?v=G4rzkF41-58 Answer 2.7: Frequency (ν) of light = 1/Period Frequency (ν) = 1/2.0 × 10–10 s = 5 × 109 s-1 Wavelength (λ) of light = c/ ν c = velocity of light in vacuum = 3×108 m/s Substituting the value in λ = c/ ν = 3 × 108 ms-1/5 × 109 s-1 λ = 6 × 10-2 m Wave number of light = 1/wavelength = 1/6 × 10-2 m = 16.66 m-1

Class 11 Chemistry Chapter 2 Question 2.1 https://www.youtube.com/watch?v=_lNTTItFsbg&t=32s Question 2.1: (i) Calculate the number of electrons which will together weigh one gram. (ii) Calculate the mass and charge of one mole of electrons. Ans 2.1: (i) Mass of one electron = 9.1 × 10–31 kg Number of electrons that weigh 9.1 × 10–31 kg = 1 Number of electrons that will weigh 1 g i.e 1 × 10–3 kg = 1 × 10–3 kg/ 9.1 × 10–31 kg = 0.1098 × 10–3 + 31 = 0.1098 × 1028 = 1.098 × 1027 (ii) Mass of one electron = 9.1 ×…

https://www.youtube.com/watch?v=wPSp-xSYWsw Question 2.4: Write the complete symbol for the atom with the given atomic number (Z) and atomic mass (A) (i) Z = 17, A = 35 (ii) Z = 92, A = 233 (iii) Z = 4, A = 9 Ans 2.4: For any given atom, we can write the symbols as AZX. Here, X is the element’s symbol, Z is its atomic number and A is its mass number. Therefore the symbols for the above elements are written as: (i) Z = 17, A = 35 Symbol: 3517Cl (ii) Z = 92, A = 233 Symbol: 23392U (iii)…

https://www.youtube.com/watch?v=6-di0ujG_Ew Question 2.3: How many neutrons and protons are there in the following nuclei? 136C, 168O, 2412Mg, 5626Fe, 8838Sr Ans 2.3: 136C Atomic mass = 13 Atomic number = Number of protons = 6 Number of neutrons = Atomic Mass – Atomic Number ∴ Number of neutrons = 13 – 6 = 7 168O Atomic mass = 16 Atomic number = 8 Number of protons = 8 Number of neutrons = Atomic Mass – Atomic Number ∴ Number of neutrons = 16 – 8 = 8 2412Mg Atomic mass = 24 Atomic number = Number of protons = 12…

Question 2.5: Yellow light emitted from a sodium lamp Question 2.5: Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm. Calculate the frequency (ν) and wave number (v¯) of the yellow light. Ans 2.5: We know λ = c/ ν c = velocity of light (3 × 108 m/s) λ = Wavelength = 580 nm = 580 × 10-9 m ν = c/ λ ν = 3 × 108 / 580 × 10-9  ν = 5.17 × 1014 s-1 Thus, the frequency of yellow light emitted from the sodium lamp = 5.17 × 1014 s–1…

Question 2.6: Find the energy of each of the photons Question 2.6: Find the energy of each of the photons which (i) corresponds to light of frequency 3× 1015 Hz. (ii) have a wavelength of 0.50 Å. Ans 2.6. We know (i) Energy (E) of a photon (E) = hν —————–A Where, h = Planck’s constant = 6.626 × 10–34 Js ν = frequency of light = 3 × 1015 Hz ν = 3 × 1015 s–1 Substituting the values of h and ν in expression A E = (6.626 × 10–34) (3 × 1015) E = 1.988 × 10–18…

Important Questions of Periodic Classification of Elements Class 11 Important Questions of Periodic Classification of Elements Class 11 Que 1. An element is present in the third period of the p-block. It has 5 electrons in its outermost shell. Predict its group. How many unpaired electrons does it have? Ans 1. It belongs to the 15th group (P). It has 3 unpaired electrons. Que 2. An element X with Z = 112 has been recently discovered. Predict its electronic configuration and suggest the group in which it is present. Ans 2. [Rn] 5f14 6d10 7s2. It belongs to the 12th…

Important Questions Class 11 Chemistry – Structure of Atom Important Questions Class 11 Chemistry Que 1. Calculate the charge of one mole of electrons. Ans 1. One electron has charge 1.602 × 10−19 coulombs one mole of electrons has charge = 6.023 × 1023 × 1.602 × 10−19 = 9.648846 × 104 = 96488.5 coulombs Que 2. Calculate the mass of one mole of electrons. Ans 2. Mass of electron = 9.1 × 10−31 kg One mole of electrons has mass = 6.023 × 1023 × 9.1 × 10−31 = 54.8 × 10−8 = 5.48 × 10−7 kg Que 3.…

Chapter 2 Science Class 9 – Questions and Answers Chapter 2 Science Class 9 Very Short Questions Que 1. Define solvent. Ans 1. The component of the solution that dissolves the other component in it is called the solvent. Que 2. Define solute. Ans 2. The component of the solution that is dissolved in the solvent is called the solute. Que 3. What is a ‘tincture of iodine’? Ans 3. A solution of iodine in alcohol is known as a tincture of iodine. It has iodine (solid) as the solute and alcohol (liquid) as the solvent. Que 4. What are…