4.3 Electrical Circuits

Question 1

What is Kirchhoff’s second law

Answer 1

In any circuit the sum of electromotive force (emf) is equal to the sum of the potential difference in a closed loop due to the conservation of energy

Question 2

What happens to current and potential difference in series

Answer 2

Current - stays the same across all components
Potential difference - splits across components so that their total is equal to the emf

Question 3

What happens to current and potential difference in parallel

Answer 3

Current - the current splits between components so that the total of each loop equals the total current
Potential difference - stays the same across all loops

Question 4

What is the equation for resistance in series and why

Answer 4

Rt = R1 + R2 …

The total resistance of a circuit is equal to the sum of resistance in each component

Question 5

What is the equation for resistance in parallel and why

Answer 5

1/Rt = 1/R1 + 1/R2 …

R1 and R2 represent the total resistance of each loop. Within each loop current is equal in each component and p.d. Is split between them

Question 6

What is internal resistance (r) and state its units

Answer 6

When not all energy transferred to charge carriers is available to the circuit

Ohms (Ω)

Question 7

What are the lost volts (v) and state their units

Answer 7

The difference between emf and pd

Volts (V)

Question 8

State the equation for emf considering current and resistance

Answer 8

emf (V) = current (A) x (resistance (Ω) + internal resistance (Ω) )

ε = I (R + r)

Question 9

State the equation for emf considering p.d.

Answer 9

emf (V) = potential difference (V) + lost volts (V)

ε = V + v

Question 10

What are the equations relating p.d. and resistance when current in constant

Answer 10

V1/V2 = R1/R2

V _out = (R2 / (R1 + R2) ) x V _in

Question 11

What are the purposes of potential dividers

Answer 11

• provide variable p.d.
• enable a specific p.d. to be chose
• split p.d. of a power source between two of more components