Electricity and magnetism Flashcards
Ferrous Materials
Attracted by magnet and can be magnetized
Eg. iron, steel, nickel and cobalt
Non-ferrous materials
Not attracted by magnet and cannot be magnetized
e. g copper, silver, aluminum, wood, glass
Electric field intensity
E is the electric field intensity in N/C
force exerted by the field on a unit
charge placed at a point around
another charge
E = f/q
Current
=> Rate of flow of charges in a 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
Voltage across the resistor is
directly proportional to current,
V⋉ I or V/I = R
V is the voltage in volts (V),
I is the current in amperes (A) and
R is resistance in ohms (Ω)
Voltage
Energy per unit charge
V = energy / Q
Q is the charge in coulombs (C),
V is the voltage in volts (V)
Energy is in joules (J)
E.M.F - Electromotive Force
e.m.f. = lost volts + terminal potential difference
EMF=Ir + IR
Resistance and resistivity
R = ρ x L/A
ρ is the resistivity of resistor in Ω.m
R is the resistance a resistor,
L is the length of a resistor in meters
A is the area of cross-section of a
resistor in m2
Circuit
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
R, R1, R2 and R3 are resistances of
resistor in ohms
Resistance in parallel
1/R = 1/R1 + 1/R2 + 1/R3
Potential divider
V1/V2 = R1/R2
Potential divider
V2 = (R2 / R1 + R2) X V
Power
P = I X V P = I2 X R P = V2/R
P is the power in Watts (W)