# 3 bulbs at different brightness

1. Sep 10, 2014

### emmfranklin

1. The problem statement, all variables and given/known data

This is a circuit i tried recently . I have recorded my observation below and i need to know why it happens like that
.....................230 V
______________(~)______________
|.....................................................|
|.....................................................|
|.....................................................|
|......62V..........130V...........38V........|
|...__(v)__.......__(v)__.......__(v)__....|
|..|...........|.....|...........|......|...........|...|
|..|...........|.....|...........|......|...........|...|
|_|__(x)__|___|__(x)__|____|__(x)__|__|
.......A................B................C
......60W.........40W............100W

Key: (x) = Bulb

(v) = voltmeter

(~) = AC Voltage

Please ignore the dotted lines ..... .I did that because otherwise the whole diagram got crumpled up when i used spaces or tabspace to make my circuit diagram.
it is very difficult to draw a circuit diagram in ascii text.
please do not consider the dots as connecting wires.
the connecting wires are | and ___

I have connected 3 Tungsten Bulbs to an AC source of 230 voltage in series. Each glows differently.
Bulb A is 60Watts, B is 40Watts, C is 100Watts.
I noticed that Bulb B is the Brightest, Bulb A is dim and Bulb C is the dimmest. (least bright). I recorded the voltage across each using a multimeter and indicated in the diagram.
The voltages measured may be up or down by 2 to 3 volts due to practical errors.

Normally the 100 W is always the brightest when compared with other bulbs in a single circuit i.e bulb is connected alone to the power source.
Q1) Why does the 40 W bulb glow the brightest?
Q2) Why is the voltmeter showing the highest reading across the 40 W bulb B?
Q3) What is the resistance in each case?
Q4) What is the current drawn ? is it different in each bulb or same .
Q5) What is the Power in each?
Q6) What is the Energy used each?

2. Relevant equations
V= IR
P= IV

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### 3 bulb circuit.jpg
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2. Sep 10, 2014

### nrqed

The first step is to determine the resistances of each light bulb (or at least, how they rank in terms of resistance). Do you see how to do this? Once you have ranked the resistances, you can rank the power in each (which determines how bright they glow) using the formula for power (here, the simplest one to use is $P = R I^2$

3. Sep 10, 2014

### CWatters

In case it's not obvious....

A bulb specified as "60W, 230W" only burns 60W when connected to 230V. If the voltage across the bulb is not 230V the power and brightness will be different.

4. Sep 10, 2014

### BvU

So, Emm, are you able to make the first step nrq proposes ? Your two equations are just fine for that: use the second one to find I for the "bulb is connected alone to the power source" (which is 230 V). Then the first one to find R.

Next you place all three in series, and you know the power ratios (from your second equation), because I is the same for each of the three. The equation nrq mentions (substitute V = IR in P = IV to get P = I2R helps you answer Q5.

5. Sep 11, 2014

### haruspex

To enter diagrams in ASCII text use 'CODE' brackets. Click on Go Advanced, then click the pound sign (in UK, called the hash symbol, #). Text inside the CODE brackets is monospaced. E.g.
Code (Text):
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