IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: NotAbod on March 23, 2011, 01:22:20 pm

Title: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 23, 2011, 01:22:20 pm: hello
i need help with Reed relay, Reed switch and LDR.
How does street lights work using LDR and a normally closed reed relay?
help me please
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 23, 2011, 07:57:52 pm: Street Lamp working:
LDR (photoresistor) resist the flow of electricity, but their resistance drops when light hits them. The more resistance in a circuit, the less electric current flows through. In a LDR powered street light, a small current runs through the resistor. When it becomes dark, the resistance increases and the current drops. Now the Reed relay which consists of "Normally Opened" relay switch is used. The low current in the circuit makes the reed relay to power the lamp with the battery in the another circuit.
::)
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 23, 2011, 08:25:10 pm: Quote from: $~SauD~$ on March 23, 2011, 07:57:52 pm
Now the Reed relay which consists of "Normally Opened" relay switch is used. The low current in the circuit makes the reed relay to power the lamp with the battery in the another circuit.
::)
thanks a alot, nut actually our school physics teacher told us that a normal closed relay is used. :-\
so which one is correct ????????
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 23, 2011, 08:42:47 pm: Quote from: Abod on March 23, 2011, 08:25:10 pm
thanks a alot, nut actually our school physics teacher told us that a normal closed relay is used. :-\
so which one is correct ????????
Won't a closed switch gets open? In open circuit current doesn't flows.
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 23, 2011, 10:07:00 pm: i donno
there are 2 circuits

During night time this circuit is drawn
_________________________ ___________street lamp______
| | | | |
| | Relay coil Relay(NC relay) |
| resistor | | |
____ |__________| |__________240v___________|
_ 12v |
| LDR
|_____________|
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 24, 2011, 09:32:55 am: Quote from: Abod on March 23, 2011, 10:07:00 pm
i donno
there are 2 circuits

During night time this circuit is drawn
_____________________________ _________street lamp________
| |     | |    |
| | Relay coil   Relay(NC relay)    |
| resistor         |         |   |
____       |____________|        |__________240v___________|
   _ 12v       |
| LDR
|_______________|
Oh, Sorry sorry
You are correct :-[
Yes, normally closed switch works in it
I am sorry.
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 24, 2011, 03:14:46 pm: no problem bro ;)
we didnt get any questions about LDR and relays today, it was phyiscs mock exam.
i was so worried about LDR, Relays and transistors xd xd
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 24, 2011, 03:30:57 pm: Quote from: Abod on March 24, 2011, 03:14:46 pm
no problem bro ;)
we didnt get any questions about LDR and relays today, it was phyiscs mock exam.
i was so worried about LDR, Relays and transistors xd xd
i had physics on Wednesday, mocks :P
Gave it without studying because i was sck >:(
i had a transistor question :-[
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 24, 2011, 03:56:39 pm: actually i have no idea about transistors.
i dont have a good physics textbook to study about transistors from it :(
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 24, 2011, 04:25:00 pm: Quote from: Abod on March 24, 2011, 03:56:39 pm
actually i have no idea about transistors.
i dont have a good physics textbook to study about transistors from it :(
Study notes and check a book named "Physics for you" by Keith Johnson. Its a good book :)
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 24, 2011, 06:03:21 pm: ok i will.
thanks for the advice.
is it availabe as ebook?
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 24, 2011, 06:31:05 pm: Quote from: Abod on March 24, 2011, 06:03:21 pm
ok i will.
thanks for the advice.
is it availabe as ebook?
I am not sure,
Let me search,
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 24, 2011, 06:51:26 pm: i am searching too....
nothing till now
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: The Golden Girl =D on March 26, 2011, 04:27:10 pm: I've got some notes on this just give me ur e-mail ID since I was not able to upload it here.
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 26, 2011, 04:36:32 pm: Quote from: ~ The Golden Girl ~ on March 26, 2011, 04:27:10 pm
I've got some notes on this just give me ur e-mail ID since I was not able to upload it here.
IGCSe? :o
Send me too, mom :D
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 26, 2011, 05:27:00 pm: Quote from: ~ The Golden Girl ~ on March 26, 2011, 04:27:10 pm
I've got some notes on this just give me ur e-mail ID since I was not able to upload it here.
THANKS
i will send my e-mail in a pm
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: ~ Miss Relina ~ on March 26, 2011, 06:10:18 pm: Quote from: Abod on March 26, 2011, 05:27:00 pm
THANKS
i will send my e-mail in a pm
and if u have got them and donot have any probs in posting them here so plz do that ;)
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: SauD~ on March 26, 2011, 06:11:45 pm: Quote from: Relina on March 26, 2011, 06:10:18 pm
and if u have got them and donot have any probs in posting them here so plz do that ;)
Yes i will do :)
Title: Re: need help with Reed relay, Reed switch and LDR
Post by: NotAbod on March 26, 2011, 06:17:31 pm: Quote from: Relina on March 26, 2011, 06:10:18 pm
and if u have got them and donot have any probs in posting them here so plz do that ;)
okz i will do that ;D