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Class 12th Physics Atoms

Imagine that the electron in a hydrogen atom is replaced by a muon (µ). The mass of muon particle is 207 times that of an electron and charge is equal to the charge is of an electron. The ionization potential of this hydrogen atom will be :

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Raj Pandey

Contributor-Level 9

E ∝ m ⇒ E / 13.6 = 207 ⇒ E = 207 * 13.6eV = 2815.2eV

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Class 12th Atoms

The atomic hydrogen emits a line spectrum consisting of various series. Which series of hydrogen atomic spectra is lying in the visible region?

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alok kumar singh

Contributor-Level 10

The Balmer series lies in the visible region of the electromagnetic spectrum.

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Class 12th Physics

A radioactive sample disintegrates via two independent decay processes having half lives T?/?¹? and T?/?²? respectively. The effective half-life, T?/? of the nuclei is:

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Raj Pandey

Contributor-Level 9

From Radioactive Decay Law,
dN/dt = λ? N + λ? N = λ_eff N
⇒ λ_eff = λ? + λ? ⇒ ln (2)/T = ln (2)/T? + ln (2)/T? ⇒ T = (T? ) / (T? + T? )
(where T, T? , and T? are half-lives)

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Class 12th Thermodynamics

The standard enthalpies of formation of Al₂O₃ and CaO are –1675 kJ mol⁻¹ and -635 kJ mol⁻¹ respectively.
For the reaction 3CaO + 2Al → 3Ca + Al₂O₃ the standard reaction enthalpy ΔᵣH° = _______ kJ.
(Round off to the nearest integer).

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Vishal Baghel

Contributor-Level 10

3CaO + 2Al → 3Ca + Al? O?
ΔH? = ΣΔH? (Products) - ΣΔH? (Reactants)
ΔH? = [ (0) + (-1675) ] - [ (3 * -635) + (0) ]
ΔH? = -1675 - (-1905) = -1675 + 1905 = 230 kJ
Ans = 230

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Class 12th Physics Electromagnetic Waves

A plane electromagnetic wave of frequency 100 MHz is traveling in vacuum along the x-direction. At a particular point in space and time, B = 2.0 * 10? k? T. (where, k? is unit vector along z-direction) What is E at this point? (speed of light c = 3 x 10? m/s)

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Raj Pandey

Contributor-Level 9

Direction of E is perpendicular to the direction of propagation and that of B.
E = cB = 3 * 10? * 2 * 10? = 6 V/m

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Class 12th Redox Reactions

15 mL of aqueous solution of Fe²⁺ in acidic medium completely reacted with 20 ml of 0.03 M aqueous Cr₂O₇^2-. The molarity of the Fe²⁺ solution is _______ *10^-2 M (Round off to the nearest integer).

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Vishal Baghel

Contributor-Level 10

Cr? O? ²? + Fe²? - (H? )-> Cr³? + Fe³?
(n=6) (n=1)
Meq Cr? O? ²? = Meq Fe²?
20 * 0.03 * 6 = 15 * M * 1
M = (20 * 0.03 * 6) / 15 = 0.24 = 24 * 10? ²
Ans = 24

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Class 12th Physics

Match List-I with List-II

List - I	List - II
(a) Phase difference between current and voltage in a purely resistive AC circuit	(i) π/2; current leads voltage
(b) Phase difference between current and voltage in a pure inductive AC circuit	(ii) Zero
(c) Phase difference between current and voltage in a pure capacitive AC circuit	(iii) π/2; current lags voltage
(d) Phase difference between current and voltage in an LCR series circuit	(iv) tan?¹((X_L - X_C)/R)

Choose the most appropriate answer from the options given below :

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alok kumar singh

Contributor-Level 10

In a purely resistive AC circuit, if V = V? sin (ωt), then the current I is:
I = (V? / X? ) * sin (ωt - π/2)

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Class 12th Physics Magnetism and Matter

Four identical long solenoids A, B, C and D are connected to each other as shown in the figure. If the magnetic field at the centre of A is 3T, the field at the centre of C would be: (Assume that the magnetic field is confined within the volume of respective solenoid).

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Raj Pandey

Contributor-Level 9

Magnetic field at centre of a solenoid is proportional to the current through it. Current through C will be one-third of the current through A. So
Magnetic field at the centre of C = 3/3 = 1T.

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Class 12th Chemistry

The reaction of white phosphorous on boiling with alkali in inert atmosphere resulted in the formation of product 'A'. The reaction of 1 mol of 'A' with excess of AgNO₃ in aqueous medium gives _______ mol(s) of Ag. (Round off to the nearest integer).

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Vishal Baghel

Contributor-Level 10

P? + 3NaOH + 3H? O → PH? + 3NaH? PO? (A)
Here, NaH? PO? is a reducing agent.
NaH? PO? + AgNO? + H? O → Ag + HNO? + NaH? PO?
Equivalents of NaH? PO? = equivalents of Ag (n-factor of NaH? PO? = 4)
1 mole * 4 = n moles of Ag * 1
So, moles of Ag = 4.

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Class 12th Physics

Two cells of emf 2E and E with internal resistance r? and r? respectively are connected in series to an external resistor R (see figure). The value of R, at which the potential difference across the terminals of the first cell becomes zero is: