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Do You Know
1. Radius of Curvature of a Spherical Mirror
The radius of curvature of a spherical mirror is related to its focal length by a simple formula.
Formula
Radius of Curvature (R) = 2 × Focal Length (f)
Given
- Focal length = 20 cm
Calculation
R = 2 × 20
R = 40 cm
Therefore, the radius of curvature is 40 cm.
Important Points
- Radius of curvature is always double the focal length
- This relation is used for both concave and convex mirrors
- The center of curvature lies on the principal axis of the mirror
Example
If the focal length of a mirror is 15 cm, then the radius of curvature will be 30 cm.
Importance
This formula is useful in solving numerical problems related to mirrors and image formation.
2. Dispersion of White Light
Dispersion is the process in which white light splits into its different component colours.
How Dispersion Occurs
When white light passes through a prism, each colour bends differently because every colour has a different wavelength.
Colours Formed
The seven colours are:
- Violet
- Indigo
- Blue
- Green
- Yellow
- Orange
- Red
Important Points
- Violet bends the most
- Red bends the least
- Together these colours form the visible spectrum
Example
Rainbow formation is a natural example of dispersion.
Importance
Dispersion proves that white light is made up of many colours.
3. Periods in the Modern Periodic Table
The Modern Periodic Table contains 7 horizontal rows called periods.
What are Periods?
Periods are horizontal rows where elements are arranged according to increasing atomic number.
Features of Periods
- Elements in the same period have the same number of electron shells
- Properties change gradually from left to right
Structure of the Periodic Table
- 7 periods
- 18 groups
Example
- First period → Hydrogen and Helium
- Second period → Lithium to Neon
Importance
The periodic table helps scientists classify and study elements easily.
4. Biodegradable Substance – Wool
Biodegradable substances are materials that can be broken down naturally by microorganisms.
Why Wool is Biodegradable
Wool is obtained from animals and decomposes naturally over time.
Examples of Biodegradable Materials
- Wool
- Paper
- Cotton
- Food waste
Non-Biodegradable Materials
- Plastic
- Glass
- Aluminum
These materials remain in the environment for a very long time.
Importance
Biodegradable materials reduce pollution and are eco-friendly.
Example
Dry leaves and food waste decompose naturally and mix with soil.
5. Heating Element of Electric Iron – Nichrome
The heating element of an electric iron is made of nichrome.
What is Nichrome?
Nichrome is an alloy made of nickel and chromium.
Why Nichrome is Used
- High resistance
- Produces heat quickly
- Can tolerate high temperature
- Does not rust easily
Working Principle
When electric current passes through nichrome wire, heat is produced due to resistance.
Uses of Nichrome
- Electric iron
- Room heater
- Toaster
- Electric stove
Importance
Nichrome is ideal for heating appliances because it is durable and heat resistant.
Summary
These concepts explain important topics related to light, chemistry, electricity, and environmental science. The radius of curvature formula helps in mirror calculations, dispersion explains the splitting of white light, the periodic table organizes elements scientifically, biodegradable substances help protect nature, and nichrome is widely used in heating appliances.