Equations Flashcards
What are the three equations that can be used to determine the Voltage in any given circuit?
I.R
(current x resistance)
P/I
(power / current)
√P.R
(square root of power x resistance)
What are the three equations that can be used to determine the Current in any given circuit?
V/R
(voltage / resistance)
P/V
(power / voltage)
√P/R
(square root of power / resistance)
What are the three equations that can be used to determine the Resistance in any given circuit?
V/I
(voltage / current)
V²/P
(voltage squared / power)
P/I²
(power / current squared)
What are the three formulae that can be used to determine the Power in any given circuit?
V.I
(voltage x current)
I².R
(current squared x resistance)
V²/R
(voltage squared / resistance)
What is the equation for calculating the total resistance (Rₜ) in a circuit with two resistors in paralell?
Rₜ = R₁xR₂ / R₁+R₂
What is the equation for calculating the total resistance (Rₜ) in a circuit with more than two resistors in paralell?
1/Rₜ = 1/R₁ + 1/R₂ + 1/R₃ … etc.
What is the equation for calculating the total resistance (Rₜ) in a circuit with more than one resistors in series?
Rₜ = R₁ + R₂ + R₃ + R₄ …etc
What is the formula for Kirchoff’s Law regarding voltage (Vₜ) in a paralell or series circuit?
Vₜ = V₁ + V₂ + V₃ + V₄ …etc
What is the formula for Kirchoff’s Law regarding current (Iₜ) in a paralell or series circuit?
Iₜ = I₁ + I₂ + I₃ + I₄ …etc.
Briefly describe Kirchoff’s voltage law (KVL).
“the sum of the voltage differences around any closed loop in a circuit must be zero”
Basically, all of the voltage that goes into a circuit must be accounted for at the end of the circuit.
Briefly describe Kirchoff’s Current law.
“the current flowing into a node (or junction) must be equal to the current flowing out of it”.
Basically, all of the current that flows into a component of a circuit must also flow out of it in a closed circuit loop.
What is the formulae that can be used to determine the resistivity (R) of a conductor?
What two other mathmatical expressions can be used to signify the relationship between resistivity and the other factors governing cable choice?
R = P x l / a
(resistivity = rho x length / area)
R ∝ l
(resistivity is proportional to length)
R ∝ 1/a
(resistivity is inversly proportional to area)
P = Rho
l = Length
a = cross sectional area
What are the two equations that can be used to work out the quantity of Charge (Q) in a circuit?
Q = I.t
(charge = current x time in seconds)
Q = V.C
(charge = voltage x coulombs)
What is the formula for calculating the total capacitance (Cₜ) of a circuit in series?
Cₜ = C₁ + C₂ + C₃ + C₄ …etc
What is the formula for calculating the total capacitance (Cₜ) of a circuit in paralell?
1/Cₜ = 1/C₁ + 1/C₂ + 1/C₃ + 1/C₄ …etc.
What is the formula for efficiency?
How is the result of the equation presented?
Efficiency = output power / inputpower
It is presented as a percentage.
What is the formula used to calculate the energy (J) in a magnetic field?
1/2.L.I²
(0.5 x inductance in henrys x current squared)
What is the equation used to calculate the force required to move an object that is accelerating at any given speed?
F = m.a
(Force = mass x acceleration)
What is the equation used to calculate the acceleration of an object?
a = d/t²
(Acceleration = distance / time²)
What is the equation used to calculate the average acceleration of any given object?
Av. a = avg. v / t
(Average acceleration = average velocity / time)
What is the equation used to calculate the force required to move an object?
F = m.a
(Force = mass x acceleration)
What is the equation used to calculate work done?
W = F.d
(Work = force x distance)
Force requires the weight of an object (ie. the mass x the acceleration due to gravity)
How do you calculate the weight (w) of an object?
w = m.g
(Weight = mass x acceleration due to gravity - 9.81)
What equation is used to calculate the power (P) of a process?
P = W/t
(Power = work done / time taken)
What calculation is used to calculate the potential energy (PE) an object possesses?
PE = m.g.h
(Potential energy = mass x gravity x height)
What calculation is used to calculate the kinetic energy (KE) of an object?
KE = m.v
(Kinetic energy = mass x velocity)
What is the equation used to calculate the efficiency of any given piece of power using machinery?
Efficiency = Output / Input
What is the equation used to calculate the input power of any given piece of power using machinery?
Input = Output / Efficiency
What is the equation used to calculate the output power of any given piece of power using machinery?
Output = Input x Efficiency¹
¹ This is expressed as a percentage, so you will need to multiply as a decimal! eg. 70% is 0.7!
What is the equation you would use to calculate the effort required to lift (E) a lever?
E = L x Ld / Ed
(Effort = (Load x load to fulcrum distance) / effort to fulcrom distance)
What is the equation you would use to calculate the Load (L) of a lever?
L = E.Ld / Ed
(Load = Effort x Load distance from fulcrum / Effort distance from fulcrum)
What is the equation you would use to calculate the distance of the load from the fulcrum (Ld) on a lever?
Ld = E.Ed / L
(Load distance = Effort x Effort distance from fulcrum / Load)
What is the equation you would use to calculate the distance of the effort from the fulcrum (Ed) on a lever?
Ed = L.Ld / E
(Effort distance = Load x Load distance from fulcrum / Effort)
How would you convert millimetres squared into metres squared?
Multiply the figure in millimetres by ten to the power of -6
What is the formula used to determine the Flux density in a magnetic field?
β = ɸ / a
(Flux density = Magnetic flux / area)
What is the formula for calculating the force on a current-carrying conductor?
F=β.I.l
(Mechanical force extered on conductor = Flux density x current x length)
What is the formula for the generation of EMF?
What is the name of the law which states this?
emf(V)=β.l.v
(Electro motive force generated = magnetic flux density x length x velocity of conductor)
The name of this law is Faraday’s Law
How would you calculate the Vrms of UK supply electricity?
0.707 x Vpeak
-or-
0.707 x 325 = 230V
How would you calculate the Vpeak of UK supply electricity?
1.414 x Vrms
-or-
1.4.4 x 230 = 325V
