Electric Circuits Flashcards
What is 1W in SI base units?
Watts = Power (P) P = VI = WI / Q =FsI / Q =FsI / It =masI / It
=kgm²s⁻²A / As
=kgm²s⁻³
What is charge?
A property that particles or objects can have.
Can be described as positive (+), negative (-), or neutral.
What is the symbol for charges?
Charge (C)
Positive (+)
Negative (-)
Define electrical current.
The rate of flow of charge.
What direction does conventional current flow in?
Positive → Negative
How does the flow of the actual electrons differ from the conventional current flow?
Opposite to conventional current flow.
How can we increase the current through a material?
Increase the rate of charges.
Define potential difference.
The energy transferred per unit charge.
Define resistance.
Opposite to the flow of charge.
Define power.
The energy transferred per unit time.
Define work done.
The energy transferred when a force is acting.
How is current quantified?
The amount of charge passing a point in a second:
I = ΔQ / Δt
One electron has a charge of ______ C.
e = -1.60 x 10⁻¹⁹C
How many electrons pass a point in a second if there is a current of 1A?
1 = ΔQ / 1 ΔQ = 1 1 electron = - 1.6 x 10⁻¹⁹ C x electrons = 1 C x = 1 / (1.6 x 10⁻¹⁹) = 6.25 x 10¹⁸
Where do the electrons come from in a circuit?
The metal from the wire.
Can we increase or decrease the amount of charges?
No, the number of charges in a circuit is a constant.
Due to the conservation of charge:
The number of charges that enter a cell or battery must be equal to the number of charges leaving a cell or battery.
In a series circuit, the current is ____ at every point.
Equal.
In a parallel circuit, the current is __1__ across __2__.
1) Split.
2) Each branch.
What is the total resistance in series?
Rₜ = R₁ + R₂ + …
What is the total resistance in parallel?
¹/Rₜ = ¹/R₁ + ¹/R₂ + …
Derive the equation for total resistance in series?
Due to the conservation of energy: the Pd supplied bu the cell is the sum of the Pd across the circuit
∴ Vₜ = V₁ + V₂ + …
Due to the conservation of charge: the current is the same across the circuit
∴ Iₜ = I₁ = I₂ = …
V=IR
∴ IₜRₜ = IₜR₁ + IₜR₂ + IₜR₃ + …
(÷ Iₜ)
Rₜ = R₁ + R₂ + R₃ + …
Derive the equation for total resistance in parallel?
Due to the conservation of charge: the total current is the sum of the currents on each branch
∴ Iₜ = I₁ + I₂ + …
Due to the conservation of energy: the Pd across the circuit must be the same
∴ Vₜ = V₁ = V₂ = …
V = IR (but I must be the subject ∵ V is a constant), I = V/R
∴ Vₜ /Rₜ = Vₜ /R₁ + Vₜ /R₂ + Vₜ /R₃ + …
(÷ Vₜ)
¹/Rₜ = ¹/R₁ + ¹/R₂ + ¹/R₃ + …
What is Ohm’s Law?
The current through a conductor between two points is directly proportional to the Pd across the two points.
What is the electromotive force?
The amount of energy a source supplies to one coulomb of charge.