Electricity Flashcards
Current is the measure…
of the amount of charge moving per second.
Current=
ΔQ/Δt
Electrons only…
drift in a random direction, so there is no net movement of charge.
When p.d. is applied across…
a conductor, a current is produced. This causes a movement of charge in one direction rather than a rapid flow.
Conventional current is…
historically from + to -
Electron flow is…
real flow from - to +
The electrical signal travels by…
electromagnetic waves, caused by the electrons.
A charge can be either…
positive or negative(ions).
Semiconductors:
- the number of charges changes with temperature
- as the temperature increases, it liberates electrons so the resistance is reduced
Series circuit:
- current is the same
- p.d. adds up
Parallel circuit:
- the current adds up
- p.d. is the same
Best conductors are:
copper, silver and gold.
Best conductors have many…
conduction electrons(delocalsied)
Number density is…
the number of conductive electrons per unit volume. (n)
Mean drift velocity is…
mean velocity of an electron (3mm/s)
Current(with number density)=
nAvq (number density x A x mean drift velocity x charge of a carrier)
A charge of electrons =
number of electrons x electron charge
A battery consists of…
many cells.
A potential difference is a measure…
of energy provided to the charge carriers.
V =
W(J) / Q(C)
P.d. between A and B is…
the energy per unit charge as the charge moves from A to B.
E.m.f. is…
electromotive force, which is the energy transferred by a source in driving unit charge around a complete circuit.
In a battery, chemical…
energy is transferred to electrical energy.
Resistance is a measure…
of the opposition, a material exerts against the flow of electrons.
R=
V/I-current
Resistance is measured in…
ohms.
The Ohm is the resistance…
of a component when a p.d. of 1V drives a current of 1A through it.
Resistance is caused by ions…
colliding with atoms.
Ohm’s law states that current…
in an ohmic conductor is proportional to the voltage across it, when temp. and other physical conditions are kept the same.
An ohmic conductor is a conductor…
that obeys Ohm’s law.
Filament lamp graph:
- for small voltages, the graph is roughly a straight line
- at a higher voltage, the line starts to curve, the gradient increases
Why does the gradient in filament lamp increases with higher voltage?
Because, the temperature increases with higher current.
Tresh-hold voltage is where…
the diode starts to conduct (0.6 V on average)
A diode in a forward direction after passing…
tresh-hold point the resistance of diode decreases rapidly.
A diode in reverse direction, the resistance…
is almost infinite so very little current.
A diode in the breakdown stage, the current…
becomes infinite, the heating effect is very big and it is destroyed.
Tresh-hold for LED is around…
2 V
LDR is…
Light-dependent resistor. It is an input transducer. Resistance decreases as light intensity increases.
Transducer is…
a device that transforms one physical quantity into another.
The resistance of LDR can fall from…
1 M ohms in darkness to 500 ohms in the light.
Thermistor is…
input transducer. Decreasing resistance with increasing temperature.
NTC is…
negative temperature coefficient thermistor. The resistance decreases with increasing temperature.
