Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
9 Cards in this Set
- Front
- Back
Charges in good electrical conductors (metal) |
Charges move relatively freely |
|
Charges in insulators (glass and ceramics) |
No mobile charges |
|
Charges in semi conductors |
Limited number of mobile charges |
|
Examples of semi conductors |
Silicon Germanium |
|
What happens to resistivity as semi conductor is heated |
Some vibrational energy is transferred to atomic electrons Some of these electrons become free to move through the material As temp increases Number of mobile charge carriers increases So resistivity decreases |
|
Rate of change of resistivity compared to metal |
Rate of change of resistivity with temperature > rate of change of resistivity of a metal Large negative number |
|
Thermistors |
Resistance decreases, temperature increases (NTC thermistors) |
|
Uses of NTC thermistors |
Car thermometers Fridges, toasters, hairdryers (thermometers) In circuits -> prevent a current surge i |
|
Light dependent resistors |
Semi conductors with small amounts of another substance (ie galium arsenide) Electrons absorb energy from light as light intensity increases More electrons mobile, resistivity decreases |