Electricity and Magnetism / Electromagnetism and Digital Electronics Flashcards
Ferrous Materials
- Definition
- Example
- Attracted by magnet and can be magnetised
- iron, steel, nickel and cobalt
(iron temporary and steel permanent)
Non-ferrous materials
- Definition
- Example
- Not attracted by magnet and cannot be magnetised
- copper, silver, aluminium, wood, glass
Electric field
The space or region around a charge where a unit charge experiences a force.
The direction is outward from (North) positive charge and inward into (South) negative charge
Electric field intensity
- Definition
- Formula
Amount force (f) exerted by the charge on a unit charge (q) placed at a point in the field.
E = F / Q
E is the electrical field intensity in N/C
Current (I): Rate of flow of charges in conductor
I = Q / t
I is the current in amperes (A),
Q is the charge in coulombs (C)
t is the time in seconds (s)
Current
In circuits the current always choose the easiest path
Ohms law
def
formula
Voltage across the resistor is
directly proportional to current,
V⋉ I
R = V / I
V is the voltage in volts (V),
I is the current in amperes (A) and
R is resistance in ohms (Ω)
Voltage (potential difference)
Energy per unit charge
V = Energy (E) / Charge (Q)
q is the charge in coulombs (C),
V is the voltage in volts (V)
Energy is in joules (J)
Resistance in terms of the resistivity of a resistor
fomula
R = p x (L / A)
R is the resistance a resistor ρ is the resistivity of resistor in Ω L is the length of a resistor in meters A is the area of cross-section of a resistor in m^2
Voltage and Current in series vs. parallel Circuits
In series circuit→ the current stays the same and voltage divides
In parallel circuit → the voltage stays the same and current divides
Resistance in series
R = R1 + R2 + R3
all represent resistances in Ω
Resistance in parallel
1/R = 1/R1 + 1/R2 + 1/R3
all represent resistances in Ω
Potential divider or potentiometer
V1 / V2 = R1 / R2
Potential divider
V1 or V2 formula
V(1 or 2) = (R2 / (R1 + R2) ) x V
Power (W)
P = I x V
P = I^2 x R
P = V^2 / R
Power (J)
P = energy / time
Diode def
Semiconductor device… current pass only in one direction, rectifier
Transistor def
Semiconductor device works as a switch , collector, base, emitter
Light dependent resistor
LED resistor dependant upon light, brightness increases when the resistance decreases
Thermistor
Resistor depend upon temperature, temperature increase resistance decrease
Capacitor
Parallel conductor with insulator in between to store charges
Relay
Electromagnetic switching device
Fleming’s RH or LH rule
Thumb direction of motion (Force)
Index finger direction of magnetic field lines
Second finger direction of current
Transformer
Vp / Vs = np / ns
Vp and Vs are the voltages; np and ns are the number of turns in primary and secondary coils
(second formula TBA)
Power in primary coil =Power in secondary coil
Ip and Is the currents in primary and secondary coil
E.M induction
Emf or current is induced in a conductor when it cuts the magnetic field lines
a.c. generator
Produce current, use Fleming’s right hand rule
d.c. motor
Consume current, use Fleming’s left hand rule
Logic gates
AND:
only 1 outcome if both inputs are 1
NAND:
opposite of AND
OR:
only 0 outcome if both inputs are 0
NOR:
opposite of OR
NOT:
1 input and output is opposite of input
Cathode rays
Stream of electrons emitted from heated metal (cathode). This process is called thermionic emission.
CRO
Horizontal or y-plates for vertical movement of electron beam.
Timebase or x-plates for horizontal movement
Emf def
energy needed to drive 1 unit of charge around a circuit
