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Download 8th Class General Science Notes (Unit # 11) for Islamabad Model Schools & Colleges

Download 8th Class General Science Notes (Unit # 11) for Islamabad Model Schools & Colleges

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Download 8th Class General Science Notes (Unit # 11) for Islamabad Model Schools & Colleges


Make a list of similarities and differences between the way the dynamo works and how a power station generates electricity.
·        Electrical energy can be produced by a machine called dynamo or generator.
·        In power station heat energy is converted to mechanical energy and mechanical energy is converted into electric current.

What are the functions of slip ring and brushes?
The ends of the coil are joined to two slip rings on the axle and against which carbon brushes press. The brushes rub against the slip rings, so that the rotating coil is connected to the bulb.

Suggest three ways in which the speed of rotation of the motor could be increased.
1)      Increase the strength of permanent magnets.
2)      Increase the size of magnet wires.
3)      Increase the number of turns (coil)

Write two disadvantages of using wind power generators.
1)   Wind turbines do not produce the same amount of electricity all the time.
2)   Wind turbines are noisy.

What is the difference between bicycle dynamo and a power station?
·        A bicycle dynamo is a power generator which employs a fixed coil generator. This generator is made by fixing the coil and rotating a coil around it.
·        While power station is huge as compared to bicycle dynamo

What is meant by alternating current?
The current induced in the coil flows first in one direction and then in the opposite direction. This type of current is called alternating current (AC).

Identify the simple devices that generate electricity in daily life.
Battery, Cell, Generator, Dynamo LED etc.

Draw a flow chart showing energy conversion in thermal power station.

Why is the energy stored in hot rocks called geothermal energy?
Geothermal energy is thermal energy generated and stored in the Earth. Therefore energy stored in hot rocks is also called geothermal energy.

Name some electronic system used in our homes and offices?
Door Bell System, Security Alarm System, Biometric Fingerprint reader system
Give three examples of transducers.
The output transducer converts the electrical energy supplied by the processor into another form. Output producers include lamps, LEDs, loudspeakers, motors, electric heaters, relays and cathode ray tubes.

When a door bell is rung, what is being used as? a) the input sensor b) the output device
Bell Button is used as input sensor and Speaker of bell is used as output device.

What is the purpose of a rectifier?
The task of turning alternating current into direct current is called rectification, and the electronic circuit that does the job is called a rectifier.

What types of problems are involved in generating electricity from fossil fuels?
(a)        Fossil fuels are non-renewable energy resources.
(b)        Fossil fuels release carbon dioxide when they burn, which increases global warming.
(c)             Coal & oil release sulphur dioxide on burning causing breathing problems.

What are the problems with generating electricity using nuclear fuel?
(a)        Nuclear fuels are radioactive materials which are nonrenewable.
(b)        The disposal of leftover radioactive waste is the greatest problem.
(c)             In case of any accident, large amounts of radioactive materials could be released into the environment which can cause fatal diseases.

Describe briefly the followings:
They conduct electricity less than conductors but more than insulators. Semiconductors exhibit both conducting and insulating properties.
They keep currents and voltages at the levels needed for other components to work properly.
They store small amounts of electric charge. It has two plates (+ve and -ve). They are used in smoothing circuits and time-delay circuits.
A diode is component that consists of two semiconductors placed side by side. A diode allows electric current to flow in one direction.
They are used for amplifying signals and for switches.
They contain many complete circuits with resistors, transistors, and other components all formed on a tiny chip. They are also called integrated circuits (ICs).
Display device:
A display device is an output device for presentation of information in visual.




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Download Class Notes: Download 8th Class General Science Notes (Unit # 11) for Islamabad Model Schools & Colleges
Download 8th Class General Science Notes (Unit # 11) for Islamabad Model Schools & Colleges
Download 8th Class General Science Notes (Unit # 11) for Islamabad Model Schools & Colleges
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