Dentists use a concave mirror.

Refraction of through glass slab:

When a ray of light passes through a glass slab, it undergoes refraction twice: once when entering the glass and once when exiting. The refraction at the second surface is such that the ray emerges parallel to its original path. This happens because the angle of incidence and refraction are equal but opposite at both surfaces, resulting in no overall deviation in the direction of the light ray. However, the ray is displaced laterally.

If no image is obtained when an object is placed 20 cm away from a convex lens, it suggests that the object is at the focus of the lens. This means the object distance (u) is equal to the focal length (f) of the lens. Therefore, the focal length of the lens is:

f = 20 cm

_glassn_air = 1/1.5 = 0.67

Thus, the refractive index of air with respect to glass is 0.67.

OR

The linear magnification ($m$) of a lens is the ratio of the image size to the object size. Given:

• Object length = 5 cm
• Image length = 10 cm

m = Image\ size\over Object\ size = 10\over 5 = 2

So, the linear magnification is 2.

Image Distance:

Magnification (m) = 2

Object distance (u) = - 2 cm

v = m × u = 2 × (-2) = -4 cm

So, the image distance is -4 cm (negative indicating the image is on the same side as the object, meaning it’s a virtual image).

Hydro-electric power generation is based on the principle of converting potential energy of stored water into kinetic energy and then into electrical energy. The basic steps are:

1. Water Storage: Water is stored at a height in reservoirs behind a dam. This water has potential energy due to its elevated position.
2. Water Flow and Turbines: When released, the water flows through pipes (penstocks), and its potential energy is converted into kinetic energy. The flowing water strikes and rotates turbines connected to a generator.
3. Electricity Generation: The rotating turbines drive the generator, converting mechanical energy into electrical energy, which is then distributed for use.

Initial voltage (V₁) = 220 V

Current (I₁) = 1 A

Voltage for the second case (V₂) = 110 V

Resistance (R) of the bulb:

R = V_1\over I_1 = 220\over 1 = 220 Ω

Current in the second case:

I₂ = V_2\over R = 110\over 220 = 0.5 A

OR

The formula for power: P = V^2\over R

For the first bulb (220V-60W):

R₁ = V^2\over P = 220^2\over 60 = 806.67 Ω

For the second bulb (110V-60W):

R₂ = V^2\over P = 110^2\over 60 = 201.67 Ω

Now, find the ratio of their resistances:

Required Ratio = R_1\over R_2 = 806.67\over 201.67 = 4

Thus, the ratio of resistance for the two bulbs is 4:1.

An α-particle consists of 2 protons and 2 neutrons. When emitted, the nucleus loses 2 protons, reducing the atomic number by 2 and the mass number by 4, forming a new element that is two places lower in the periodic table.

γ-ray emission only releases energy without changing the number of protons or neutrons. Since the atomic number remains unchanged, no new element is formed.

Dobereiner’s law of triads states that in a group of three elements (a triad) with similar chemical properties, the atomic mass of the middle element is approximately the arithmetic mean of the atomic masses of the other two elements.

The oxidizing power of these halogens increases as follows:

I < Br < Cl < F

OR

Important Conclusion of Moseley’s Experiment

Moseley’s experiment established that the atomic number (not atomic mass) defines an element’s identity, as X-ray frequencies corresponded to atomic numbers.

Importance of the Periodic Table

This led to the periodic table being organized by atomic number rather than atomic mass, resolving previous inconsistencies and accurately reflecting element properties.

In electrolytic refining of copper, the impure copper rod is used as the anode.

Chemicals Used in Industrial Production of Urea

1. Ammonia (NH₃)
2. Carbon Dioxide (CO₂)

Balanced Chemical Equation

2NH₃ ​ + CO₂ ​ →NH₂ CONH₂ ​+ H₂O

In this reaction, ammonia and carbon dioxide react to form urea and water.

(A): Since (A) adds one molecule of bromine per molecule, it must be an alkene with the general formula C₂H4.

The structural formula of (A) is:

Ethene: CH₂ ​=CH₂ ​

(B): Since (B) adds two molecules of bromine per molecule, it must be an alkene with the general formula C₂H₂​.

OR

Balanced Chemical Equation:

NaOH + CH₃​COOH → CH₃​COONa + H₂​O

Jute is more environmentally friendly for packaging compared to polythene. This is because jute is a natural, biodegradable fiber that decomposes quickly, while polythene is a synthetic plastic that can take hundreds of years to break down, contributing to environmental pollution.

The structural formula of (B) is:

Ethyne: HC≡CH

Balanced Chemical Equation for (B) with Bromine

HC ≡ CH + 2Br₂ → CHBr₂ − CHBr₂

In this reaction, ethyne reacts with two molecules of bromine to form 1, 2 - dibromoethane

Solar energy is a non-conventional energy source used to generate electricity.

The SI unit of electric power is the watt (W).

Nitric acid (HNO₃) is manufactured using the catalytic oxidation of ammonia.