Question

A transformer supplies 12V when connected to a 240V mains. If this transformer takes a 0.55A from the mains when used to a light five 12V, 24W lamps in parallel

Wts its efficiency ?

what the cost of using it for 10hrs at 15c per kw/h ?

Answer 1

@IhteshamMalik

Answer 2

can someone just tell me the formula for finding the efficiency

Answer 3

Effiecincy = power output / input power

Answer 4

ik but I'm talking about in terms of the values
power input = 6.6W------> is that ri8?
power output = 24W

Answer 5

and for ideal case... Power input = Power Output

Answer 6

No power output is always less that the power input

Answer 7

For ideal case they may equal.

Answer 8

Mathematically...... Power input = power output .>>>> V I = V' I'

Answer 9

where V is the input voltage and I is the input Current and V' is the output voltage and I' is the output current.

Answer 10

yes i know that but as u said the power input is always greater then the power output then this means the answer is 3.36?

Answer 11

Now i am solving your numerical..... in your question V = 240 v and I = 1.55 A

Answer 12

but only 12V is supplied

Answer 13

wait, gonna to solve this one... V' = 12 V and I' = ?? I' we have to find.

Answer 14

we know that POwer = VI now V = 12V and P = 24 watt.... input is 240 volts..

Answer 15

From P = VI I' = P / V = 24 / 12 = 2 A so you have I' = 2 A

Answer 16

V = 240 V I = 1.55 A V' = 12 V I' = 2A

Answer 17

oh ri8

Answer 18

Now its done?

Answer 19

its 0.55A not 1.55A

Answer 20

@RANE

Answer 21

thank you

Answer 22

yh?

Answer 23

Okay... welcome... :)

Answer 24

r u doing majors in physics ?

Answer 25

I am doing Master In physics. With Quantum mechanics... Alhamdulillah

Answer 26

nyc
best of luck

Answer 27

Thanks... :)

Answer 28

and if I'm not wrong u r paki ri8?

Answer 29

Yes... You are right. And you from?

Answer 30

by the way, How you guess that i'm from Pakistan.

Answer 31

im also form pakistan
by your name.... ihtesham pakistani naam hai

Answer 32

Oh that's good. so i met first Pakistani at open study.,

Answer 33

In which class are you??

Answer 34

im yr 12
really? u haven't met ay paki other then me ?

Answer 35

yes really i hadn't met any body before,

Answer 36

A level??

Answer 37

there is no levels in Australia like pakistan

Answer 38

You are from Pakistan, but in Australia?

Answer 39

yh im Pakistani but i live in Australia
which prt of pak r u form ?

Answer 40

Punjab, Faisalabad

Answer 41

And you belong to?

Answer 42

Lahore

Answer 43

Hmm neighbours... :D

Answer 44

yh .....

Answer 45

And any question??

Answer 46

how does this electric bell works ?
http://www.google.com.au/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=iJCvzL8Fotg7gM&tbnid=wP3fq05OqpP6iM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.controlcircuitdiagram.com%2Fschematicelectrical.com%2F2010%2F12%2F03%2Fcircuit-diagram-of-electric-bell%2F&ei=FlN4U46jNpfd8AWUvoKoCg&bvm=bv.66917471,d.dGc&psig=AFQjCNFSM6ccVjhlFchdSOPlF5danLZVjQ&ust=1400480883527482

Answer 47

okay, it is the phenomenon reated to electro magnet

Answer 48

An electric bell works when an electrical current flows through an electromagnetic coil. when an eclectic current passes through a coil, a magnetic fileld produces..

Answer 49

As you see, there is an iron core inside the coil. this iron becomes megnetized. and act as an electromagnet. while passing the current through the coil, this core remains magnetized and act as magnet.

Answer 50

This causes a piece of iron inside the bell o be attracted to the electromagnet and when it is, it strikes the side of the bell housing.

Answer 51

http://en.wikipedia.org/wiki/File:Electric_Bell_animation.gif

Answer 52

In this animation a strip Name "A" is attracted by the iron core which is acting as a magnet.... when core attracts the strip, this other end of the strip touched the "B". and bell starts ringing....

Answer 53

hmm get this??

Answer 54

yup thank u

Answer 55

wait

Answer 56

This will be helpful for you.

Answer 57

Most Welcome ..