Sensing Flashcards
What is the relationship stated by Ohm’s law?
Current is directly proportional to voltage
On a current voltage graph, does a shallow gradient have lots or little resistance?
Lots of resistance
What happens to the resistance of thermistors & LDR’s when temperature/light is increased?
Their resistance decreases
In a filament lamp, what happens to resistance when current is increased and why?
More current causes the temp. to increase, and so the resistance increases as the particles vibrate more with more energy
What determines a material’s conductivity?
The number of charge carriers (free electrons or ions) there are per cubic metre
Do conductors have high or low density of mobile charge carriers?
Very high density
What happens to a conductor when the temp. is increased and why?
The number of charge carriers remains the same but the lattice vibrates more so electrons are scattered and less free to move, so conductivity decreases
What happens to a semiconductor’s conductivity when the temp. is increased?
More electrons are freed to conduct so conductivity rapidly increases. The lattice still vibrates like in a conductor but its effect is small compared to the huge increase in charge carriers.
What are 3 equations for EMF?
E = V + v E = I(R+r) V = E - Ir
In an EMF and internal res. investigation, why do you sometimes turn off the current, via a switch?
To reduce current briefly to prevent wires heating up too much which would increase the resistance
When do semiconductors not conduct?
When at a temp. of -273 K
What is the potential divider equation?
Vout = (R2/R1 + R2) X Vin
What is a potentiometer and when is it useful?
Just a potential divider but with variable resistors. Useful for changing a voltage continuously, like volume control on a radio
Why do voltmeters have a very high resistance?
To ensure they don’t affect the circuit by discouraging current from flowing through the parallel connection of the voltmeter
Define current
The number of coulombs transferred per second
