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1. Concave Mirror Used by Dentists
Dentists use a concave mirror to see a larger image of teeth.
Why concave mirror is used:
- It forms a magnified image when the object is placed close to the mirror
- Helps dentists examine teeth clearly
Properties of concave mirrors:
- Can produce enlarged images
- Reflect light inward toward a focus point
Other uses:
- Shaving mirrors
- Headlights of vehicles
- Solar furnaces
Example:
Dentists use concave mirrors to check cavities and small details in teeth.
2. SI Unit of Electric Potential Difference – Volt
Electric potential difference is measured in volts (V).
Meaning of potential difference:
It is the work done to move a unit charge from one point to another in an electric circuit.
SI Unit:
Volt (V)
Named after:
Alessandro Volta, a famous scientist.
Measuring device:
A voltmeter is used to measure potential difference.
Example:
A household battery may have a potential difference of 1.5 volts.
3. Greenhouse Gas – Carbon Dioxide
Carbon dioxide (CO₂) is one of the main greenhouse gases present in the atmosphere.
How greenhouse gases work:
They trap heat from the Sun and warm the Earth’s atmosphere.
Sources of carbon dioxide:
- Burning fuels
- Vehicles
- Factories
- Deforestation
Effects of excess greenhouse gases:
- Global warming
- Climate change
- Rising temperatures
Importance:
A small amount is necessary to maintain Earth’s temperature, but excess amounts are harmful.
4. Focal Length of a Plane Mirror – Infinity
The focal length of a plane mirror is considered to be infinity.
Reason:
A plane mirror has a flat surface, so reflected rays do not meet at a single point.
Understanding focal length:
Focal length is the distance between the mirror and its focus point.
In plane mirrors:
- Radius of curvature is infinite
- Therefore focal length is also infinite
Image properties:
- Virtual and erect
- Same size as the object
5. Ozone Layer Depletion – CFCs
Chlorofluorocarbons (CFCs) are mainly responsible for the depletion of the ozone layer.
What is the ozone layer?
It is a protective layer in the atmosphere that absorbs harmful ultraviolet (UV) rays from the Sun.
Sources of CFCs:
- Refrigerators
- Air conditioners
- Aerosol sprays
Effects of ozone depletion:
- Increased UV radiation reaching Earth
- Skin diseases and eye damage
- Harm to plants and animals
Prevention:
Reducing the use of CFC-based products helps protect the ozone layer.
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