Urgent Physics Assistance Needed!

[abcde]

AOA!

One of the syllabus components is: "discuss the environmental and cost implications of underground power transmission compared to overhead lines".
Where can I get information on this? It isn't mentioned in our book. Please provide detailed info on this if you can.
Secondly, the syllabus also requires us to: "describe and explain the action of reed relays in switching circuits". Are reed relays the same as the 'normally-open' type relays?

 

[scouserlfc]

WOA!

i think you search for reed relays on the internet like wikipedia and other helpful websites.

I copied this from wikipedia its the simple definition.I dont know if it helps you or not but its up to you if u find it informative.

Reed relay
A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas-filled glass tube which protects the contacts against atmospheric corrosion; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid. Reed relays can switch faster than larger relays, require only little power from the control circuit, but have low switching current and voltage ratings.


Just wanted to know what book do you use for physics??

 

[Nibz]

AOA!

One of the syllabus components is: "discuss the environmental and cost implications of underground power transmission compared to overhead lines"

W.S
Underground Power Transmissions are mostly used in areas of glorious natural beauty, where the overhead cables would damage the environment by spoiling the landscape. However, these underground cables are very much expensive to lay compared to overhead cables. Overhead cables are the cheapest way of transmitting power over long distances ( Air is the best insulator )
For underground cables, it is very difficult to insulate and so they use lower voltage. To transmit the same power, they have to carry a higher current. This also means they must be thicker. (another cost implication)
I hope this explanation helps!

n I think 'scouserlpc' has already answered ur 2nd question.

 

[UxaiR]

Wasalam! Just Wanted to Add Some more points

 

[UxaiR]

Notes by Me on Reed relay

 

[abcde]

Thankyou so much everyone!

 

[abcde]

@scouserlfc: i use the GCE Physics Matters.
@ everyone: one more question: (f) describe the use of an astable circuit (pulse generator).
(g) describe how the frequency of an astable circuit is related to the values of the resistive and capacitative
components.
What's an astable? Can anybody please answer these?

 

[abcde]

more over i want to know the uses of a bistable. Please answer!

 

[Nibz]

@ everyone: one more question: (f) describe the use of an astable circuit (pulse generator).
(g) describe how the frequency of an astable circuit is related to the values of the resistive and capacitative
components.
What's an astable? Can anybody please answer these?

An astable circuit has no stable state, i.e it changes from one state to the other at a constant rate.
Uses of astable circuit => it is used as a pulse generator (as u mentioned)
=> It can also be used in "Indicator Lights" of vehicles etc

Frequency of astable circuit = k/ (R)(C) [read it as k over (R into C)]

 

[Nibz]

more over i want to know the uses of a bistable. Please answer!

And a bistable circuit has two stable states. It can be made using two NAND gates or two NOR gates (I hope u know these).
It is used in: => COUNTERS (shop counters);
=> and in electrical memories in computers.

 

[abcde]

Can you kindly umm show me how an astable circuit looks like? :S

 

[Nibz]

This circuit is made using two NAND gates (P and Q), a resistor (R) and a capacitor (C).
When the power is on, the output signal will be vibrating at a fixed frequency.
The function of this circuit can be explained as: A high voltage input to the Gate P gives low output to P. Since the output from Q is high, the input of Q is low, resulting in the chjarging of the capacitor through R. as the Capacitor gets charged, the input of Q rises. At a certain point, the output 4m Q swicthes to low value. The input of P therefore becomes low, and the output 4m it becomes high. The Capacitor now begins to discharge thru R in the reverse direction, resulting in a low output to Q and high output 4m it. the input of P then becomes high, and the output from it becomes low. this cycle is repeated again n again.

The output signal from "P" thus vibrates with a steady FREQUENCY "f" which is inversely proptional to the resistance of the resistor and the capicitance of the capacitor.
f=k/CR