Drift Velocity, Insulators, Semi-Conductors, and Conductors Flashcards
How do metallic bonds work and how do they define metal properties?
In metals attractive forces are strong due to the regular lattice and high melting point. Each atom contributes at least one electron which becomes delocalised, creating a strong metallic bond.
When PD is applied to a conductor, how does the resistance change?
Electrons move with random velocities. With a PD across the lattice, they experience force and drift to the anode, the rate of flow in current. As temperature rises, positive ions vibrate more in conductors, increasing resistance.
What is the drift velocity formula?
I = vAnq
Why do insulators have high resistance?
Insulators have electrons and charges but they can’t move. When glass is heated, sodium ions are freed, and these can conduct.
How do semi-conductors change when temperature rises?
Semi conductors have 1 in 10^12 atoms ionised. When heated, more are ionised, increasing number density of electrons, and so conductivity.
How does resistance change in filament lamps?
As PD rises, current rises at a declining rate. While filament is coiled up metal wire and expected to act like a conductor, current increases the temperature, and so resistance rises.
How does resistance change with temperature for NTC thermistors?
In thermistors, these are used as temperature sensors. NTC thermistors have falling resistance with temperature. Increasing temperature is achieved through more current.
How do diodes work?
Diodes only allow current in one direction. Forward bias is the direction current flows in. Forward bias requires threshold voltage 0.6V. In reverse bias, current is tiny. At a high enough voltage, the diode will break down, making current infinite.
