Chapter 4 - Electric current Flashcards
What formula relates charge, current and time?
Q=It
Define current
Rate of flow of charge (due to passage of charge particles)
How do you work out the number of electrons passing for a given charge?
Times it by the charge of the electron
What is the structure of an insulator?
Each electron is attached to the atom
What is the structure of a conductor?
Free charge carriers (electrons/ions)
What is the structure of semi-conductors?
The number of free electrons increases with temperature (as they gain more energy to break free of the shells)
What is the formula relating energy, voltage and charge?
E=VQ
What is the formula relating current, resistance and voltage?
V=IR
What is Ohms law?
V=IR
Define the term potential difference
The work done/ energy transferred per unit of charge
Define the term electromotive force
Electrical energy predicted per unit of charge passing through the source
What is the formula relating power, current and voltage/resistance?
P=IV=IIR
What is the formula relating power, energy and time?
Power = Energy/time
What is the formula relating resistivity, resistance, area and length?
resistance = (resistivity*length)/area
Define the term superconductor
A material with 0 electrical resistance
Define the term transition temperature
The temperature at which a material loses its superconducting ability
Define the term critical temperature
The temperature at which and below a materials resistance = 0
What are the applications of superconductors?
Efficient power lines/ cables
High power electromagnets with very strong magnetic fields
Define the term diode
Very high resistance in 1 direction but very low in the other
What happens as temperature increases on a thermistor?
Resistance descreases
In metals what happens when temperature increases? Explain why
Resistance increases as cations have more kinetic energy so electrons cannot pass through as easily
Why do metals have a positive temperature coefficient?
As temperature increases, resistance increases
Why do semi conductors have a negative temperature coefficient?
As temperature increases, resistance decreases
Why are thermistors often used as temperature sensors?
Its % change of resistance per kelvin is much greater than that of a metal
