Class 11th

Given below are two statements:

Statement I : The pH of rain water is normally $\sim 5.6$

Statement II : If the pH of rain water drops below 5.6, it is called acid rain.

In the light of the above statements, choose the correct answer from the options given below

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Payal Gupta

Contributor-Level 10

Both statements are true when pH decreases from 5.6 then it becomes more acidic hence it is called Acid rain.

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7 months ago

Class 11th Oscillation

The potential energy (U) of a diatomic molecule is a function dependent on r (interatomic distance) as $U = \frac{α}{r^{10}} - \frac{β}{r^{5}} - 3$

Where, and are positive constants. The equilibrium between two atoms will be ${(\frac{2 α}{β})}^{\frac{a}{b}},$ ${\frac{}{}}^{\frac{}{}}$ where a =…………….

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Contributor-Level 10

For equilibrium,

$\frac{d U}{d r} = 0 \Rightarrow \frac{- 10 α}{r^{11}} + \frac{5 β}{r^{6}} = 0 \Rightarrow r = {(\frac{2 α}{β})}^{\frac{1}{5}}$

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7 months ago

Given below are two statements:

Statement I : An allotrope of oxygen is an important intermediate in the formation of reducing smog.

Statement II : Gases such as oxides of nitrogen and sulphur present in troposphere contribute to the formation of photochemical smog.

In the light of the above statements, choose the correct answer from the options given below:

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alok kumar singh

Contributor-Level 10

Primary pollutants are oxides of N & C and classical smog is due to SO₂ & particulates of fossil

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7 months ago

The same size images are formed by a convex lens by a convex lens when the object is placed at 20cm or at 10cm from the lens. The focal length of convex lens is ……………cm.

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Contributor-Level 10

Image is virtual, when an object is placed at distance 10 cm from the lens and image is real when object is placed at 20 cm from the lens.

Thus, m₁ = -m₂ => $\frac{f}{f - 10} = \frac{- f}{f - 20} \Rightarrow f = 15 c m$

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7 months ago

Class 11th Thermodynamics

In a certain thermodynamical process, the pressure of a gas depends on its volume as kV³. The work done when the temperature change from 100°C to 300°C will be……………. nR, where n denotes number of moles of a gas.

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Contributor-Level 10

P = kV³ Þ PV^-3 = k Þ Polytropic Process with index m = -3

W = $\frac{n R (T_{2} - T_{1})}{1 - m} = \frac{n R (300 - 100)}{1 - (- 3)} = 50 n R$ .

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7 months ago

Which of the following compound is added to the sodium extract before addition of silver nitrate for testing of halogens?

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Payal Gupta

Contributor-Level 10

NaCN converted into HCN and Na₂S converted into H₂S

$\begin{array}{l} N a C N + H N O_{3} \to N a N O_{3} + H C N \\ N a_{2} S + 2 H N O_{3} \to N a N O_{3} + H_{2} S \end{array}$

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7 months ago

An engine of a train, moving with uniform acceleration, passes the signal – post with velocity u and the last compartment with velocity $υ .$ The velocity with which middle point of the train passes the signal post is:

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Contributor-Level 10

Assume the length of train be I and its acceleration be a.

$v^{2} = u^{2} + 2 a l \Rightarrow a l = \frac{v^{2} - u^{2}}{2}$

Velocity when middle point crosses the post,

$V_{m} = \sqrt[]{u^{2} + 2 a \frac{l}{2}} . = \sqrt[]{u^{2} + \frac{v^{2} - u^{2}}{2}} = \sqrt[]{\frac{u^{2} + v^{2}}{2}}$

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7 months ago

The correct order of bond dissociation enthalpy of halogens is

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Payal Gupta

Contributor-Level 10

Bond dissociation enthalpy is the energy required to break 1 mole of bond according to experimental data

Bond energy : Cl₂ > Br₂ > F₂ > l₂

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7 months ago

Two satellites A and B of masses 200kg and 400kg are revolving round the earth at height of 600km and 1600km respectively. If T_A and T_B are the time periods of A and B respectively then the value of T_B – T_A :

[Given : radius of earth = 6400km, mass of earth = 6 * 10²⁴kg]

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Contributor-Level 10

$T = 2 π \sqrt[]{\frac{r^{3}}{G M_{e}}}$

$T_{B} - T_{A} = \frac{2 π}{\sqrt[]{G M_{e}}} (r_{B}^{3 / 2} - r_{A}^{3 / 2}) = \frac{2 * 3.14}{\sqrt[]{6.67 * 1 0^{- 11} * 6 * 1 0^{24}}} [{(8 * 1 0^{6})}^{\frac{3}{2}} - {(7 * 1 0^{6})}^{\frac{3}{2}}]$

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A student is performing the experiment of resonance column. The diameter of the column tube is 6cm. THE Frequency of the tuning fork is 504 Hz. Speed of the sound at the given temperature is 336m/s. The zero of the meter scale coincides with tip end of the resonance column tube. The reading of the water level in the column when the first resonance occurs is:

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