(National Book Foundation - New Book/New Syllabus Based on National Curriculum Pakistan 2023-2024 and Onwards)
(Class 8 General Science Notes for 8th Centralized Exam 2023-2024 and onward, FDE, Islamabad)
(Class 8 General Science Notes for 8th Centralized Exam 2023-2024 and onward, FDE, Islamabad)
C. Long Questions
Q1. What is the spherical mirror type used in the solar cooker? How it can be used to cook food?
Ans:
In solar cookers, the concave spherical mirror is used. In a concave spherical mirror, the inner surface of the spherical section is made reflecting. A beam of light is directed towards a concave mirror along its principal axis. After reflecting from the mirror, the ray converges to a single point in front of the mirror called the focus point F.
By using a concave mirror we can direct the energy in sunlight to a single point. This reflected light is very powerful because it carries a lot of thermal energy.
Solar cookers are one of the simplest utensils used to cook food. It harnesses the power of the sun to cook food.
Q2. What is a wind turbine? How it is used to produce electricity?
Ans:
A wind turbine is a large vanned (covered with feathers) wheel rotated by the wind to generate electricity.
Production of electricity through wind turbine:
To change the wind energy into electricity, the wind should turn the rotor blades, which need to spin the turbine. An electric generator is fitted inside the turbine, which is a rotating machine that supplies an electrical output with voltage and current. A wind turbine is connected to the motor and its movement generates electricity.
The power produced by a wind turbine depends on
- Elevation (height)
- Wind speed
- Air temperature
Q3. What is UPS? Where and how is it used?
Ans:
UPS stands for Uninterruptible Power Supply. It is also known as battery backup. It is an electrical device that provides emergency power when regular power fails or voltage drops to an unacceptable level.
A UPS allows for the safe, shutdown of a computer and other appliances. Its size and design determine how long it will supply power. It detects loss in the primary power source. The control is transferred to the batteries and DC voltage in batteries is converted to AC using an inverter.
Plug the charger into the wall and power it ON make sure the inverter is powered OFF.
Attach and test the inverter if it is separate from the charger. Hook up the cables to the batteries, noting polarity. Turn the inverter on and test it with some suitable AC load.
Take a UPS system and connect it with a bulb as a load. After charging for some time turn OFF the power to the UPS, and the light will continue glowing.
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Unit-11: Technology in Everyday Life: Solved Short Questions and Answers
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