4.3 electrical circuits Flashcards
what is Kirchoff’s Second Law?
Kirchoff’s Second Law states that in any closed loop. the sum of the e.m.f is equal to the sum of the products of the current and the resistance
(in other words the total potential difference is equal to the sum of all the potential differences of the components)
∑Ɛ = ∑IR
what is Kirchoff’s First law?
Kirchoff’s First law states the sum of currents entering a junction in a circuit is equal to the sum of the currents leaving the junction
what is Kirchoff’s Second Law a consequence of?
the conservation of energy
what is Kirchoff’s First Law a consequence of?
the conservation of charge
what is the equation for total resistance in a parallel circuit?
1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3 opposite to capacitors and spring constants
what is the equation for total resistance in a series circuit?
Rtotal = R1 + R2 + R3
opposite to spring constant and capacitors
how are ammeters connected in circuits and what is the resistance of them?
how are ammeters connected in circuits and what is the resistance of them?
how are voltmeters connected in circuits and what is the resistance of them?
connected in parallel, designed to have close to infinite resistance so that none of the current flows through them
what is the rule for voltage in series circuits?
splits, the voltage of the cell is equal to the sum of the voltages across the components (not necessarily and equal split)
what is the rule for current in series circuits?
stays the same
what is the rule for current in parallel circuits?
splits at junctions
what are the steps for solving circuit analysis questions using Kirchoff’s law’s?
draw a diagram
find the largest source of EMF
draw the loops of current all going from and back to the largest source of EMF
pick 2 loops that come from this source of EMF
use kirchoff’s first law and a junction to set up an equation
use kirchoff’s second law to form another equation
use ohm’s law to express voltages in terms of current
eliminate one of the unknowns in the equation from kirchoff’s second law using the first equation
solve simultaneously
what is the rule for voltage in parallel circuits?
the same, each branch has the same voltage as the cell (so would split if there were more than one component on the same branch)
what is the rule you must remember for directions in circuits when doing analysis questions using Kirchoff’s Laws?
∑Ɛ = ∑IR
for Ɛ:
If the EMF is in the SAME DIRECTION as the loop (i.e loop goes from positive to negative terminals of cell) = positive value
If the EMF is in the OPPOSITE DIRECTION as the loop = negative value
for potential difference, V:
If the current is in the SAME DIRECTION as the loop = negative value
If the current is in the OPPOSITE DIRECTION as the loop = positive value
what is internal resistance?
internal resistance of a source of e.m.f is the resistance to electric current of the materials inside, when current flows energy is transferred to these materials resulting in the p.d dropping
