3.5.1.4 Circuits

Question 1

What is Kirchhoff’s fist law?

Answer 1

Conservation of charge:
Total charge flowing into a junction in a given time is equal to the total charge leaving a junction in the same time. So the algebraic/ vector sum of currents is zero

Question 2

Represent Kirchhoff’s first law mathematically

Answer 2

I_1+I_2+I_3+…. =0
(currents in are positive, currents out are negative)

Question 3

What is Kirchhoff’s second law?

Answer 3

Conservation of energy:
The sum of the e.m.f is the total energy produced in the loop per unit charge and the sum of the p.ds is the total energy dissipated in the loop per unit charge.
Around a closed loop, the algebraic sum of emfs is equal to the algebraic sum of the p.ds

Question 4

Represent Kirchhoff’s second law mathematically

Answer 4

SigmaEpsilon = Sigma IR

Question 5

What is resistance like in a series circuit?

Answer 5

R_tot = R_1 + R_2 + R_3 +….

Question 6

What is resistance like in a parallel circuit?

Answer 6

1/R_tot = 1/R_1 + 1/R_2 + 1/R_3 +…

Question 7

What is the total e.m.f. for cells connected in series and parallel?

Answer 7

epsilon = epsilon_1 + epsilon_2 + epsilon_3 +……

Question 8

What is the basic formula for power in electrical circuits?

Answer 8

P = IV

Question 9

What are the other equations for power?

Answer 9

P = (V^2)/R
P = (I^2)R

Question 10

What are the equations for energy transferred in a circuit?

Answer 10

E = IVt
E = ((V^2)/R)t
E = (I^2)Rt
(all derived from power equations ;p)