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Appropriate arrangement of light meter circuit with LDR and resistor question:

  • Thread starter Caiti
  • Start date
  • #1
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Homework Statement



If you have a series 'light-meter' circuit with a cell EMF of 12V that must include both an LDR and a resistor only (in series), which way would you put them around to make this most effective and why?

~~~That is, would you have LDR then resistor, or resistor then LDR? And what would be the reasoning for this.

Homework Equations


n/a


The Attempt at a Solution



If you have a series 'light-meter' circuit with a cell EMF of 12V, wouldn't the appropriate arrangement of a resistor and an LDR be to have the positive end of the battery connected to the LDR and then the resistor, as opposed to having a resistor and then LDR? I can't work out why though.
 

Answers and Replies

  • #2
gneill
Mentor
20,801
2,778

Homework Statement



If you have a series 'light-meter' circuit with a cell EMF of 12V that must include both an LDR and a resistor only (in series), which way would you put them around to make this most effective and why?

~~~That is, would you have LDR then resistor, or resistor then LDR? And what would be the reasoning for this.

Homework Equations


n/a


The Attempt at a Solution



If you have a series 'light-meter' circuit with a cell EMF of 12V, wouldn't the appropriate arrangement of a resistor and an LDR be to have the positive end of the battery connected to the LDR and then the resistor, as opposed to having a resistor and then LDR? I can't work out why though.
Hi Caiti, Welcome to Physics Forums.

I don't see any "meter" in your light-meter :smile: Perhaps the answer lies in knowing how one is to interpret the "reading" from this device.
 
  • #3
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Hi Caiti, Welcome to Physics Forums.

I don't see any "meter" in your light-meter :smile: Perhaps the answer lies in knowing how one is to interpret the "reading" from this device.
Hey,
While I totally agree with your comment, this is a question I've pulled straight from a book of them - and there is definitely no additional information there. I'm assuming the exact way of measuring light was to be disregarded; however I'm obviously not certain about this.
 
  • #4
gneill
Mentor
20,801
2,778
Hey,
While I totally agree with your comment, this is a question I've pulled straight from a book of them - and there is definitely no additional information there. I'm assuming the exact way of measuring light was to be disregarded; however I'm obviously not certain about this.
Well, why don't you propose a method of interpreting a 'reading' from the circuit? What kinds of things might be measured in an operating circuit? Do you want your reading to be larger when there's more light, or less light? What varies in an LDR with changes in light, and how does it vary?
 

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