resistance and resistivity Flashcards
State Ohm’s Law in words.
- for an ohmic conductor at a constant temperature
- current is directly proportional to the voltage across it
Describe the effect of increasing temperature on resistance.
increases
Explain why components have a higher resistance at a higher temperature.
- higher temperature = more kinetic energy
- particles vibrate with a greater amplitude
- more frequent collisions between free charge carriers & ions
- more disruption therefore harder for current to pass through
State the name of the component that is used to vary the current in the circuit.
variable resistor
Identify how the resistance changes as the current is increased in a filament lamp.
The resistance increases because the lattice ions vibrate more.
Explain how a diode works.
- only allows current to flow through it in one direction.
- as resistance is infinitely high in the opposite direction
Describe the IV graph for a diode.
for negative potential difference, no current flows
Describe resistance when an LDR is in the dark.
resistance is high
as no. of free charge carriers are low
State the actual name for a thermistor.
thermal resistor
Explain what is meant by NTC.
negative temperature coefficient:
resistance decreases as temperature increases
State the relationship between light intensity and resistance in an LDR.
The resistance of an LDR (light dependent resistor) decreases as the light intensity increases.
The equation for the resistance, R, of a section of wire of length L and cross-sectional area A is…
R = ρL/A where ρ is the resistivity
Describe and explain what happens to the resistance of a thermistor as its temperature increases.
decrease in resistance
more charge carriers released at high temperature
