Conservation of Charge & Energy in Circuits

Question 1

Is charge conserved in a circuit?

Answer 1

YES

Question 2

Is it TRUE that charge into a junction equals the charge out of the junction?

Answer 2

YES

Question 3

Define Current?

Answer 3

Current is rate of flow of charge

Question 4

What is Kirchoff’s 1st Law

Answer 4

The total current entering a junction = the total current leaving it

Question 5

What two values must be equal for energy to be conserved in a circuit?

Answer 5

E.M.F

Potential Difference

Question 6

What does Kirchoffs 2nd Law state?

Answer 6

Total E.M.F around a SERIES circuit = the sum of the PD’s across each component

(Energy is conserved)

Question 7

What is the equation for Resistance in a series circuit?

Answer 7

R (total) = R1 + R2 + R3

Question 8

What is the equation for Resistance in a Parallel circuit?

Answer 8

1/R (total) = 1/R1 + 1/R2 + 1/R3

Question 9

How to calculate the equation of a Series Circuit? R(total) = R1 + R2 + R3

Answer 9

1 - Same current at all points of the circuit (because there are no junctions)
2 - E.M.F is split between components (by Kirchoff’s 2nd Law) ℰ = V1 + V2 +V3
3 - V = IR so I is constant
4 - IR (total) = IR1 + IR2 + IR3
5 - Cancelling the I’s gives R (total) = R1 + R2 + R3

Question 10

How to calculate the equation of a Parallel Circuit? 1/R (total) = 1/R1 + 1/R2 + 1/R3

Answer 10

1 - Current is split at each Junction so I = I1 + I2 + I3
2 - Same PD across all components (Within a loop the E.M.F equals the sum of individual PD’s)
3 - V/R (total) = V/R1 + V/R2 + V/R3
4 - Cancelling the V’s gives

1/R (total) = 1/R1 + 1/R2 + 1/R3