• All solids are made up of vibrating atoms
  • The higher the temperature, the faster these atoms vibrate

   

• Electric current is the flow of free electrons in a material
  • The electrons collide with the vibrating atoms which impede their flow, hence the current?decreases

   

Metal atoms and free electrons at low and high temperatures

• So, if the current decreases, then the resistance will increase (from?V?=?IR)
• Therefore, for a metallic conductor which obeys Ohm's law:
  • An?increase?in temperature causes an?increase?in resistance
  • A?decrease?in temperature causes a?decrease?in resistance

   

• This is?not?the case for components such as a thermistor
  • For a thermistor, an?increase?in temperature causes a?decrease?in resistance

   

• A thermistor is a non-ohmic conductor and sensory resistor whose resistance varies with temperature
• Most thermistors are negative temperature coefficient (ntc) components.
  • This means that if the temperature?increases,?the resistance of the thermistor?decreases?(and vice versa)

   

• The temperature-resistance graph for a thermistor is shown below

Graph of temperature against resistance for a thermistor

• Thermistors are temperature sensors and are used in circuits in ovens, fire alarms and digital thermometers
  • As the thermistor gets?hotter, its resistance?decreases
  • As the thermistor gets?cooler, its resistance?increases

   

The resistance through a thermistor is dependent on the temperature of it

? ? ?ANSWER: A

• The resistance of the thermistor increases as the temperature decreases
• Since the thermistor and resistor?R?are connected in series, the current?I?in both of them is the same
• Ohm’s law states that?V?=?IR
• Since the resistance of the thermistor increases, and?I?is the same, the potential difference?V?across it increases
• Therefore, statement?A?is correct