Principles of electricity Flashcards
Definition of current flow
The flow of excited valance electrons in a specific direction is also referred to as current flow
Definition of Ampere
An amp(A) is a unit of electric current equal to a flow of one coulomb(C) per second (s)
The definition of potential difference
The potential difference(PD) the voltage measured across the terminals of an electrical energy of a closed circuit.
Definition of coulomb
The coulomb is a unit of electrical charge equal to the quantity of electricity conveyed in 1 second by a current of 1 A
Definition of Volt
The Volt is the potential difference between two points of a conducting wire carrying a constant current of 1A when the power dissipated between these points is equal to 1W
Definition of electromotive force
EMF is the voltage measured across the ends of a voltage source of an open circuit, that is, when no current is flowing
What are the sources of electromotive force
Cells or batteries
Generators
Solar energy
Heat
Friction
Definition of potential difference
PD is the voltage measured across the terminals of an electrical energy source of a closed circuit
Definition of resistance
Resistance is the opposition that a substance offers to the flow of electrical current. in the process of resisting current flow, heat is produced
Definition of Ohm
The ohm(Ω) is the unit of electrical resistance(R), transmitting a current 1A when subjected to a potential difference of 1V
What are the different groups of materials used in the electrical industry?
•Conductors
•Insulators
•Semiconductors
What is a conductor
It is any substance that allows current to flow through it
What is an insulator?
Give examples.
It is any substance that does not allow current to pass through it. it has an extremely high resistance
•Glass
•Ceramic
•Paper
•PVC
•Asbestos
•Mica
•Porcelain
What is a semiconductor?
Give examples.
They have conducting properties that lie between those of conductors and insulator. usually used for diodes and transistors
•Germanium
•Silicon
What is resistance used in electric Circuits for?
To produce voltage drops
To limit current flow
Definition of ohms law
The current flowing in any closed circuit is directly proportional to the voltage producing it and inversely proportional to the resistance of the circuit, provided the temperature remains constant
Definition of power
Power is defined as the rate at which work is done or the rate at which energy is consumed
Definition of energy
The capacity for doing work
Definition of joules law
The heat generated an electric circuit is proportional to the products of
- The square of the current
- The resistance of the circuit
- The time during which current flows
Q = I²Rt
Definition of joule
Is the energy dissipated as heat when an electric current (A) passes through a resistance (Ω) an equivalent amount of time (t)
Name the factors that influence the resistance of a conductor?
•Length (l)
•Resistivity (ρ)
•cross-sectional area (a)
•Temperature (t)
How does length effect Resistivity?
the resistance of a conductor is directly proportionalto its length.
the longer the higher the resistance.
How does the cross sectional area effect the resistance?
The Resistance is inversely proportional to the cross sectional area.
the bigger the smaller the resistance.
name materials that experience an increase in resistance with an increase in temperature?
•silver
•Copper
•gold
•aluminum
name materials that experience an decrease in resistance with an increase in temperature?
•Carbon
•electrolytes
•silicon and germanium
•asbestos
•mica
•porcelain
•PVC
•bakelite
What are the characteristics of magnetic lines of flux?
•always flow from the North Pole to the south pole
•always form closed loops
•behave like stretched elastic bands, Always trying to shorten themselves •they never intersect one another
•when two are flowing parallel in the same direction they will repel each other
•They are vector quantities
What are the types of Magnets?
•natural magnets
•permanent magnets
•electromagnets
What is Kirchhoff’s first law?
Kirchhoff’s current law
The Sum of the currents flowing towards any junction equals the sum of the currents flowing away from that junction.
What is Kirchhoff’s second law?
Kirchhoff’s voltage law
the sum of the applied EMFs in a closed circuit equals the sum of the voltage drops.
What is Norton’s theorem?
Any two-terminal active network containing voltage sources and resistances, when viewed from its output terminals, is equivalent to a constant-current source in parallel with a resistor.
Define magnetic flux density
The amount of magnetic flux (ϕ) passing through a specific area.
Name the ways an EMF can be induced in a conductor or a coil?
•Dynamically
•Statically
Name the requirements for an EMF to be induced?
•magnetic field lines
•a coil or conductor
•some type of motion
name the types of statically induced EMF?
•mutually induced EMF
•self-induced EMF
Name Lenz’s Law
The direction of the induced EMF is always such that it tends to set up a current opposing the charge of flux responsible for inducing it.
Define magnetomotive force
mmf
The work done in moving the unit magnetic pole (1Wb) once around the magnetic circuit.
Define magnetic field strength
The magnetomotive force per unit length of the flux path.
Define magnetic reluctance
The ratio of magnetomotive force (mmf) to magnetic flux (ϕ)
Define electromagnetic induction
The process of producing an electromotive accepts a coil linked to a changeover magnetic field.
What is Faraday’s first law?
An electromotive force (EMF) or open circuit voltage is always induced in a coil whenever the magnetic flux linking with the coil changes.
What is Faraday’s second law?
The magnitude of the induced EMF is dependant on the taste of change of flux linkages.
What is the right-hand rule for a conductor? and what is another method you can use?
If you hold a conductor in your right hand with your thumb pointing in the direction of the flow of current,
the fingers curled around the conductor will point in the direction of the Magnetic field.
The screw rule
The direction the screw travels is the direction current flows in. and the way it rotates shows the direction of Magnetic flux.
Name the ways to strengthen the Magnetic field around a solenoid.
•increase the number of turns in the coil
•increase the current through the coil
•use thicker wire
•inserting an iron core into the coil
What is the right-hand grip rule for a coil?
If you hold a coil in your right hand with your fingers pointing in the direction of the flow of current, your outstretched thumb will point to the north pole of the electromagnet.
Describe Fleming’s left hand rule?
When you hold the thumb, index and middle finger on your left hand at right angles.
then point your index finger in the direction of magnetic field
and point your middle finger in the direction of current
then your thumb will point in the direction of force exerted on the conductor.
Describe Fleming’s right hand rule.
When you hold the thumb, index and middle finger on your right hand at right angles.
then point your index finger in the direction of magnetic field
and point your thumb in the direction of force exerted on the conductor.
then your middle finger will point in the direction of current
Definition of Charge
The quantity of electricity.
Measured in Coulomb (C)
What makes a good conductor?
give some examples.
They have low resistance values.
•Gold
•Silver
•Copper
•Aluminum
What makes a poor conductor?
give some examples.
They have high resistance values.
•Steel
•Lead
•Tungsten
Give the Formulas for Ohm’s Law.
• V = IR
• R = V/I
• I = V/R
What are the Formulas for calculating Power?
• P = VI
~ P = (IR)I = I²R
~ P = V(V/R) = V²/R
What are the Formulas for Joule’s Law?
• Q = Pt
• Q = I²Rt
• Q = VIt
• Q = (V²/R)t
How do you calculate the cost of electricity?
• xkWh
Formula for efficiency.
η = Pₒ/Pı × 100%
State the formula for calculating Internal Resistance
Vᵢₙₜ = Ir
What is the formula to calculate the area of a circular object?
• a = πr²
• a = πd²/4
State the formula for calculating the resistance of a conductor
R = ρl/a
What are the units for converting into m?
•Mega(M) ~ ×10⁶
•Kilo(k) ~ ×10³
•mili(m) ~ ×10⁻³
•micro(μ) ~ ×10⁻⁶
•nano(n) ~ ×10⁻⁹
•pico(p) ~ ×10⁻¹²
State the formulas to determine the final resistance, if 0°C.
Rₜ = R₀(1 + α₀t)
R₁/R₂ = (1 + α₀t₁)/(1 + α₀t₂)
State the formulas to determine the final resistance, when initial resistance is θ°C.
•Rₜ = R_θ + ΔR
=R_θ + α_θ(t - θ)
=R_θ[1 + α_θ(t - θ)]
Formula for calculating magnetic flux density.
β = ϕ/a
Formula for calculating the magnitude of the force of a conductor inside a magnetic field
F = βIl sin θ
Formula for magnetomotive force
mmf = NI
State the formula for calculating magnetic field strength.
•H = mmf/l
•H = NI/l
State the formula for calculating magnetic reluctance.
•S = mmf/ϕ
•S = NI/ϕ
How is EMF dynamically induced?
It is produced as a result of physical movement
State the formula for calculating the magnitude of a dynamically induced EMF.
e = βlv sin θ
Describe statically induced emf
An EMF is statically induced when no physical motion is needed to induce an EMF in a coil or conductor, but the magnetic field around the conductor changes instead
Define inductance
Inductance(L) is the property of an electric circuit or coil that causes an EMF to be produced (generated or induced) in it is a result of a changing magnetic flux. Inductance opposes changes in the electric current flowing through it.
State the formula for calculating the magnitude of self-induced EMFs
E = (-LΔI)/t
State the formula for calculating the inductance of a coil
L = NΔϕ/ΔI
What are the factors influencing the capacitance of a capacitance?
•Size of plates:
~The larger the plates, the larger the capacitance
~The smaller the plates, the smaller the capacitance
•Distance between the plates:
~The further the distance, the smaller the capacitance
~The closer the distance, the greater the capacitance
•Type of dielectric material:
~Materials with greater permittivity produce greater capacitance
~Materials with lesser permittivity produce lesser capacitance
Formula for calculating capacitance
C = Q/V
Formula for the relationship between current and charge
I = Q/t
How do you calculate the total capacitance of capacitors in series?
Cₜₒₜₐₗ = (C₁ × C₂ × C₃)/(C₁C₂ + C₁C₃ + C₂C₃)
How do you calculate the total capacitance of capacitors in Parallel?
Cₜₒₜₐₗ = C₁ + C₂ + C₃
