Circuit Rules

Question 1

What is the junction rule?

Answer 1

At any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction.

Question 2

What is the rule for current in series?

Answer 2

• Current entering a component is the same as the current leaving the component.
• Components do not use up current.
• Charge per second entering a component is the same as the charge second leaving the component.

Question 3

What is the rule for current in parallel?

Answer 3

• Current passing through two or more components in series is the same through each component.
Why:
• Rate of flow of charge between each component is the same at any instant.
• Same amount of charge passing through any one component each second passes through every other component each second.

Question 4

What is the potential difference defined as?

Answer 4

• Energy transfer per coulomb of charge that flows from one point to the other.

Question 5

What are the potential difference rules?

Answer 5

• If the charge carriers lose energy, the potential difference is a potential drop.
• If the charge carriers gain energy ( e.g. through passing through a battery or a cell) , the potential difference is a potential rise equal to the pd across the battery or the cell’s terminals.

Question 6

What is the potential difference rule for charge carriers that lose energy?

Answer 6

• Potential difference is a potential drop.

Question 7

What is the potential difference rule for charge carriers that gain energy?

Answer 7

• If the charge carriers gain energy, the potential difference is a potential rise equal to the pd across the battery of cell’s terminals.

Question 8

What is the rule for potential difference for series?

Answer 8

For two or more components in series, the total pd across all the components is equal to the sum of the potential differences across each component.

Question 9

What is the rule for potential difference in parallel?

Answer 9

Pd across components in parallel is the same.

Question 10

What is the potential difference for a battery in series with three resistors?

Answer 10

• if a battery is in series with three resistors, p.d. across battery terminals is equal to the sum of the potential differences across the three resistors.
• pd across each resistor is the energy delivered per coulomb of charge to that resistor.
• Sum of p.d. across the three resistors is the total energy delivered to the resistors per coulomb of charge passing through them, which is the p.d. across the battery terminals.

Question 11

What is the rule for potential difference of a complete loop of a circuit?

Answer 11

• For any complete loop of a circuit, the sum of the emfs round the loop is equal to the sum of the potential drops around the loop.
• Total emf in a loop is the total electrical energy per coulomb produced in the loop
• Sum of potential drops is the electrical energy per coulomb delivered round the loop.