Physics
Define 'Electrical Current'
The rate of flow of charge
Define a coulomb
The flow of charge in a time of 1 second
What is the elementary charge of an electron
1.6 * 10^-19 coulombs
what is conventional current
The rate of flow of charge from the positive terminal to the negative terminal
What is electron flow
The flow of electrons from negative to positive
State Kirchoff's first law
The sum of the current entering a node is equal to the sum of the current exiting that node
Define mean drift velocity
The average velocity of electrons as they travel down a wire, colliding with positive metal ions
Give the formula for charge (Using the mean drift velocity)
I = nAve
n = Density of the material(no, of free e- per unit of volume)
A = Cross-Sectional area of the wire
v = mean drift velocity
e - Electron charge
What is the difference between insulators and conductors (in terms of density)
conductors have high densities
insulators have smaller values
semiconductors have inbetween values
Define 'Potential Difference'
The energy transferred per unit of charge where energy is transformed from electrical into other forms
define a volt
1 joule of energy transferred per coulombs
Define 'EMF'
The energy transferred per unit of charge where energy is transferred from a power supply into electrical energy
Define 'Resistance'
The potential differnce across a component divided by the current in the component
Define an ohm
1 volt per unit ampere
State Ohm's law
For a metallic conductor kept at a constant temperature, the courrent of a wire is directly proportional to the potential difference across it
Give the formula for resistivity
- RA/l
R - Resistance (Ωm)
A - Cross-Sectional Area
l - length
What is the link between resistance and resistivity
They're directly proportional
Give the formula for total no of electrons
Charge / e(electron charge)
Give the 3 formulae for Power
P = W/T
P = VI
P = 1²R
P = V²/R
W - Work Done
V - Voltage
I = Current
T - Time
Define 'Electrical Power'
The work done per unit of time
State Kirchoff's Second law
In any circuit the sum of the EMF is equal to the sum of the potential difference in a closed loop
A source of emf has internal resistance, what does this means
Not all energy transferred to the charge carriers are available to the circuit as some is transferred to the internal resistance of the cell
Define 'lost volts'
The difference between the measured potential difference across terminals of the power supply, and the actual EMF of the cell
What does kirchoffs first law demonstrate
Conservation of charge
What is the resistivity of a material
The physical property of the material
Give the formula for voltage (in a potential divider circuit)
V(out) = [R2/(R1+R2)] * V(in)
In an LED, what features change if you use an LED of a higher frequency
The threshold voltage (voltage needed to emit light) increases
What does forward bias & reverse bias mean?
Forwards bias - Where current flows in the direction of the arrowhead symbol on the diode
Reverse bias - Where current cannot flow as the arrowhead is in the opposite direction the current is meant to flow
Give 2 purposes of a potential divider circuit
- To provide a variable potential difference
- To allow a specific potential difference to be chosen