Go Back   Physics Help Forum > High School and Pre-University Physics Help > Electricity and Magnetism

Electricity and Magnetism Electricity and Magnetism Physics Help Forum

Like Tree2Likes
  • 1 Post By oz93666
  • 1 Post By oz93666
Reply
 
LinkBack Thread Tools Display Modes
Old Mar 2nd 2018, 11:49 AM   #1
Junior Member
 
Join Date: Feb 2018
Posts: 10
What is the current based on the graph?


The graph is current produced when the certain light bulb connected to voltage.

When V = 12Volt, current = 3.5 A
So the R for light bulb = 3.5 ohm

Now, that certain light bulb connected to 5ohm resistor and voltage 12 V.

I guess that Power consumed by the light bulb is P.
P = I^2R = V^2/R = VI. I am not sure which formula to use.

After light bulb connected to 5ohm and 12 V
current = 12/8.5 = 1.4 A

P = I^2R = 6.86 Wt
P = VI = 16.8 Wt
P = V^2/R = 41.14 Wt

Could it be Volt used is not 12 V
But only Volt in light bulb?
V = IR = 1.4*3.5 = 4.9 V

So, P = V^2/R = 6.86 Wt
P = IV = 1.4*4.9 = 6.86 Wt

But my answer is wrong..

Last edited by helly123; Mar 3rd 2018 at 08:33 AM.
helly123 is offline   Reply With Quote
Old Mar 2nd 2018, 08:13 PM   #2
Senior Member
 
Join Date: Apr 2017
Posts: 410
The current read from the graph when V=12 is about 3.42 , nearly 3.5

This graph cannot relate to the circuit since resistance is 5 ohms plus resistance of light , current must be less than 2.4A
studiot likes this.
oz93666 is offline   Reply With Quote
Old Mar 3rd 2018, 08:34 AM   #3
Junior Member
 
Join Date: Feb 2018
Posts: 10
Sorry, i forgot to mentioned before, that the graph is relation between the current in light bulb when connected to voltage.
Then later the light bulb connected to 5ohm and voltage 12 V
helly123 is offline   Reply With Quote
Old Mar 3rd 2018, 11:41 PM   #4
Senior Member
 
Join Date: Apr 2017
Posts: 410
from the graph we see the resistance of the light varies when the voltage across it is changed ...

you have found the resistance of the light (3.5 ohms) when the voltage across just it is 12V ....

Now we have a 5 ohm resistor in series ... the voltage across both it and the light is 12 ...

This means the voltage across the light is less than 12 V and your value for it's resistance is no longer true!!

Now what ya gona do ???
studiot likes this.
oz93666 is offline   Reply With Quote
Old Mar 4th 2018, 07:16 PM   #5
Junior Member
 
Join Date: Feb 2018
Posts: 10
Since R remains unknown, V and I remains unknown
helly123 is offline   Reply With Quote
Old Mar 4th 2018, 07:37 PM   #6
Senior Member
 
Join Date: Apr 2017
Posts: 410
Let's try guessing ...

Perhaps the current is 2A ....

From the chart we see the voltage across the lamp is 2V when current is 2A

V=IR .... resistance of lamp at 2 A is 1 ohm

In the the whole circuit we have R for the lamp 1 ohm plus 5 ohm = 6 ohm

And 6 ohm is just what we need to get 2 A from 12 V ....magick!!!

There should be a more professional way of getting the answer , butI can't think of it at the moment.
oz93666 is offline   Reply With Quote
Old Mar 6th 2018, 03:59 AM   #7
Junior Member
 
Join Date: Feb 2018
Posts: 10
I see, thanks anyway
helly123 is offline   Reply With Quote
Old Mar 6th 2018, 07:30 AM   #8
Senior Member
 
Join Date: Oct 2017
Location: Glasgow
Posts: 260
It looks like the diagrams come from a book. Is there any chance you could scan the whole page and link it here? It might help shed some light on the problem

XD
benit13 is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Electricity and Magnetism

Tags
based, circuit, current, graph, power consumed, resistor



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Current-Voltage Graph engchunh Electricity and Magnetism 1 Dec 11th 2013 02:01 PM
Current-time graph engchunh Electricity and Magnetism 2 Dec 2nd 2013 05:50 AM
drawing a velocity time graph and displacement time graph. davie08 Kinematics and Dynamics 1 Feb 27th 2011 09:18 PM
DIference of Table based on Temperature and Table based on Pressure thipos Advanced Thermodynamics 2 Feb 24th 2010 09:18 AM
Velocity Graph to Position Graph strgrl Kinematics and Dynamics 1 Apr 8th 2009 11:06 PM


Facebook Twitter Google+ RSS Feed