Help Needed: Working Out Resistor Size for Potential Divider

Click For Summary

Discussion Overview

The discussion revolves around determining the appropriate resistor size for a potential divider in the context of an AS level coursework project. Participants explore the requirements for input and output voltages, as well as the application of the circuit in a sensor design that activates a bulb based on light levels.

Discussion Character

  • Homework-related, Technical explanation

Main Points Raised

  • One participant asks for assistance in calculating the resistor size for a potential divider without prior knowledge of the process.
  • Another participant notes that the required resistor size depends on the desired input and output voltages.
  • A participant mentions that the input voltage is 9 volts, but the output voltage is uncertain, as the circuit is designed to activate a bulb when light levels drop.
  • It is suggested that one component of the potential divider will be a Light Dependent Resistor (LDR), and that values from the LDR are necessary to determine the resistor value.
  • The equation for the voltage output of a potential divider is provided, referencing standard AS textbooks.
  • A later reply recommends using a Variable Resistor (VR) instead of a fixed resistor to allow for adjustments based on light requirements, while noting the need to calculate the VR range.

Areas of Agreement / Disagreement

Participants generally agree on the need for specific input and output voltage values to determine the resistor size, but the exact output voltage remains unresolved. There are differing views on whether to use a fixed resistor or a variable resistor.

Contextual Notes

The discussion does not resolve the specific output voltage needed for the sensor circuit, and the implications of using an LDR and a variable resistor are not fully explored.

Steph191290
Messages
29
Reaction score
0
i am currently doing my as level coursework and for part of it i need to work out what size resistor to use in a potential divider but i have no idea how anyone that could help i would be really grateful,,

thanx
steph xx
 
Physics news on Phys.org
It depends what one wants to do with the potential divider. That is, what is the input voltage and the output voltage that you want?
 
umm.. well we have to put 9 volts in but I am not sure what voltage out,, we are making a sensor,, we are designing the ciruit so when the light level fall too low a bulb will switch on
 
Well one part of the potential divider will be an LDR. You'll need to know some values from the LDR and how the NOT gate operates before you can work out what value of resistor you wish to place in the potential divider. The equation for the voltage output of a potential divider is given in your AS textbooks as:

[tex]V_{out} =\frac{R_2}{R_1+R_2} V_{in}[/tex]
 
thank you i have the values from the ldr,, that is the equation i needed i just couldn't remember it thanks for your help.. xxx
 
P.S. I would place a Variable Resistor (VR) in place of a fixed resistance, so it can be altered to suit the requirments. You'll still need to work out your VR range though, but you'll gain the advantage of making adjustments to the amount of light needed.
 

Similar threads

  • · Replies 29 ·
Replies
29
Views
5K
  • · Replies 32 ·
2
Replies
32
Views
4K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 33 ·
2
Replies
33
Views
5K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K