electricity chp 9 Flashcards
electric current
the rate of flow of charge in a wire/component
charge
a property of matter and can be positive and negative
conventional current
current flowing from positive side to negative side
power
the transfer of energy
resistance
blockage of the movement of electrons
joule heating
the heating effect of when a current passes through a resistor
ohm’s law
for a metallic conductor at room temp, the current is proportional to the potential difference across it
resistivity
property that describe the extend to which a material can oppose to the flow of electric current
use of thermistor
resistor that is sensitive to high temperatures
EMF
Energy transferred by a source per unit charge around a complete circuit
Potential difference
Energy transferred per unit charge as it passes through a component
Forward bias
Positive voltage across diode, allowing current to flow
Reverse bias
Negative voltage across diode, blocking current flow
Reverse bias
Potential diff switched, negative voltage across diode
Difference between EMF and PD
- emf measured in open circuit, pd in closed
- emf is cause of pd, pd is effect of emf
- emf no energy loss, pd yes energy loss (resistance)
I-V characteristic of metallic conductor at constant temp
- follows ohm’s law
- I-V graph is straight line (constant resistance)
- slope represents resistance
- only linear when temp is constant (inc temp, inc resist)
I-V characteristic of semiconductor diode
- doesn’t follow ohm’s law
- in forward bias, current remains small until voltage reaches threshold
- in reverse bias, small leakage of current flows until breakdown od voltage is reached
- graph is highly asymmetric with significant current flowing only in forward direction after threshold voltage is surpassed
Why do diodes not follow ohm’s law
- current stays small until voltage reaches a certain level, then increases quickly
- current can only flow in one direction
- variable resistor
