Electricity- charge and current Flashcards
(20 cards)
What is the smallest unit of charge, e?
-1.6 x10^-19 C
What happens to like charges ?
They repel
What happens to opposite charges ?
They attract
What carries the charge in an electrolyte?
ions
What is the definition of electric current ?
The rate of flow of charge
What is the equation for current?
Current = Charge / Time
How must ammeters be connected ? and what resistance should they have?
In series
Low resistance
In which direction does conventional current flow?
From the positive to the negative terminals of the circuit
In which direction do the electrons flow?
Negative to positive
What are the charge carriers in metals?
Delocalised (free) electrons
How to the charge carriers in electrolytes move?
Positive ions move in the direction of the conventional current. Negative ions move in the opposite direction of conventional current.
What are semiconductors?
Materials that have a small number of free electrons at room temperature but whose resistivity falls as temperature rises
What are two examples of semiconductors?
silicon and germanium
What is Kirchhoff’s first law?
The sum of the currents entering a junction is equal to the sum of the currents leaving a junction. (This is a consequence of the conservation of charge)
When batteries stop working, what have they run out of??
energy (not charge!!)
How does current behave in a parallel circuit?
Current splits at each junction. The current at each junction depends on the p.d. across the branch and the resistance of the branch. Current recombines at the end of each junction.
How does current behave in a series circuit?
current is the same the whole way round
Are electron drift velocities relatively low or high? and why/
Low. This is because the electrons do not move in a straight line
In semiconductors, is the drift velocity higher or lower than in metals? and why?
Much higher, because the density of charge carriers in semiconductors is much lower than in metals.
What is the equation relating current and drift velocity?
I =naev
n = density of charge carriers a = cross-sectional area of the wire e = elementary charge on the electron (1.6 x10^-19 C) v = drift velocity I = current
