Potential Dividers

• When two resistors are connected in series, the potential difference across the power source is shared between them

  
• The potential difference across each resistor depends upon its resistance:

  • The resistor with the largest resistance will have a greater potential difference than the other one
  • If the resistance of one of the resistors is increased, it will get a greater share of the potential difference, whilst the other resistor will get a smaller share
• • A potentiometer is a single component that (in its simplest form) consists of a coil of wire with a sliding contact, midway along it

  A) coil of wire

  B) sliding contact

  
• The sliding contact of a potentiometer has the effect of separating the potentiometer into two parts – an upper part and a lower part – both of which have different resistances

  • If the slider in the diagram is moved upwards, the resistance of the lower part will increase and so the potential difference across it will also increase

  
• When two resistors are connected in series, through Kirchhoff’s Second Law, the potential difference across the power source is divided between them
• Potential dividers are circuits which produce an output voltage as a fraction of its input voltage
• Potential dividers have two main purposes:

  • To provide a variable potential difference
  • To enable a specific potential difference to be chosen
  • To split the potential difference of a power source between two or more components
• Potential dividers are used widely in volume controls and sensory circuits using LDRs and thermistors
• The potential difference (V) across each resistor depends upon its resistance R:

  • The resistor with the largest resistance will have a greater potential differencet han the other one from V = IR
  • If the resistance of one of the resistors is increased, it will get a greater share of the potential difference, whilst the other resistor will get a smaller share
• Potential divider circuits are based on the ratio of voltage between components. This is equal to the ratio of the resistances of the resistors in the diagram below, giving the following equation:

  • The input voltage V(in) is applied to the top and bottom of the series resistors
  • The output voltage V(out) is measured from the centre to the bottom of resistor R2
• Potential divider equation:

  A) V out

  B) R2

  C) R1+R2

  D) Vin

  
• In potential divider circuits, the p.d across a component is proportional to its resistance from V = IR
• When thinking about potential dividers, remember that the higher the resistance the more energy it will take to 'push the current through' and therefore the higher the potential difference

  • if a component (often shown as a voltmeter in questions) needs to be switched on by a change such as increased light or temperature, then the resistor it is in parallel with needs to become larger compared to the other resistor
• Potential divider - an arrangement that delivers a proprotion of the voltage from a battery

  • voltage is shared in series circuits
• Variable resistor in a series values the total resistance

  • adjusts the share of the voltage
  • can be used to be a light dimmer
  • as resistance is changed, the voltage through the bulbs change
• Amount of resistors / by total amount of resistors = the amount of voltage it gets
• The p.d.s across 2 resistors are in proportion to their resistance in a potential divider

  • R1/R2 = V1/V2
• Potential divider equation using resistance

  • V2/V = R2/R1+R2 or V(out) = R2/R1+R2 x V(in)
• Transducers - converts energy from 1 type to another

  • e.g. lightbulb
• Thermistor - resistor that changes based on tempearture

  • current increases as temperature increases, vice versa
  • input transducer
• Symbol of thermistor

  
• Thermistor doesn’t obey Ohm’s law

  • isn’t direcly linear
  • changes resistance based off temperature so as current is ran through it, it loses energy because it heats
• LDR (light dependent resistor) - resistance changes based off ligh intensity

  • input transducer
  • made from cadmium sulfide and the resistance decreases as brightness increases
• LDR symbol

  
• Less resistance means voltage decreases