Series & Parallel Circuits Flashcards

All 32 cards in this deck

What is a series circuit?

A circuit in which the components are connected one after another in a single loop, so there is only one path for the charge to follow.

What is a parallel circuit?

A circuit in which components are connected on separate branches, so the charge has more than one path to follow.

In a series circuit, what is true about the current through each component?

There is the same current through each component.

In a series circuit, what happens to the potential difference of the power supply?

It is shared between the components — the component potential differences add up to the supply potential difference.

In a parallel circuit, how does the total current from the supply relate to the currents in the branches?

The total current through the whole circuit is the sum of the currents through the separate components.

What is the total resistance of two resistors connected in series?

e.g. a $3\ \Omega$ and a $5\ \Omega$ resistor in series

The sum of the two resistances: $R_{total} = R_1 + R_2 = 3 + 5 = 8\ \Omega$.

How does the total resistance of two resistors in parallel compare with their individual resistances?

The total resistance is less than the resistance of the smallest individual resistor.

What effect does adding another resistor in series have on the total resistance of a circuit, and why?

It increases the total resistance — the charge still has only one path, and it must pass through both resistances, so the resistances add.

What effect does adding another resistor in parallel have on the total resistance of a circuit, and why?

It decreases the total resistance — there are more paths for the charge to flow, so the total current is greater for the same potential difference.

True or false? The total resistance of two resistors in parallel is found by adding their resistances.

False. Adding resistances only works in series; in parallel the total resistance is less than the smaller resistor.

What are the steps to find the current in a series circuit using equivalent resistance?

e.g. a $6\ V$ battery with a $2\ \Omega$ and a $4\ \Omega$ resistor in series

1. Add the resistances: $2 + 4 = 6\ \Omega$
2. Use $I = \frac{V}{R}$: $I = \frac{6}{6} = 1\ A$

What are the steps to find the potential difference across one resistor in a series circuit?

e.g. a $2\ \Omega$ and a $4\ \Omega$ resistor in series with a current of $1\ A$

1. The current is the same through every component: $1\ A$
2. Use $V = IR$ for that resistor: $V = 1 \times 2 = 2\ V$ across the $2\ \Omega$ resistor

Which quantity is the same for every component in a series circuit, and which is the same in a parallel circuit?

Series: the current is the same. Parallel: the potential difference is the same.

True or false? If one lamp breaks in a parallel circuit, the lamps on the other branches go out too.

False. The other branches are still complete circuits, so those lamps stay lit (in series they would all go out).

True or false? In a parallel circuit every branch carries the same current.

False. Every branch has the same potential difference, but a branch with greater resistance carries a smaller current.

In a dc series circuit used to test a component, where are the ammeter and the voltmeter connected?

The ammeter is connected in series with the component; the voltmeter is connected in parallel across the component.

What does it mean if a set of repeat readings of total resistance is precise?

The readings show little variation — they are close together, so the range is small.

What are the frequency and potential difference of the UK domestic mains electricity supply?

A frequency of $50\ Hz$ and a potential difference of about $230\ V$.

What is an alternating potential difference (ac)?

A potential difference that repeatedly changes direction, so the current it produces also keeps changing direction.

What is a direct potential difference (dc)?

A potential difference that is always in the same direction, so the current flows in one direction only.

True or false? A cell or battery supplies an alternating potential difference.

False. Cells and batteries supply a direct potential difference; mains electricity is the ac supply.

What colour is the insulation of the live wire in a three-core cable?

Brown.

What colour is the insulation of the neutral wire in a three-core cable?

Blue.

What colour is the insulation of the earth wire in a three-core cable?

Green and yellow stripes.

What is the function of the live wire, and what is its potential difference relative to earth?

It carries the alternating potential difference from the supply; this is about $230\ V$ relative to earth ($0\ V$).

What is the function of the neutral wire, and what is its potential?

It completes the circuit; it is at, or close to, earth potential ($0\ V$).

What is the function of the earth wire, and what is its potential?

It is a safety wire that stops the appliance becoming live; it is at $0\ V$.

A switch in a mains circuit is open. Why is the live wire still dangerous?

It is still at about $230\ V$ relative to earth, so touching it could make a current flow through your body to earth.

What is the danger of providing a connection between the live wire and earth?

The large potential difference (about $230\ V$) drives a large current through the connection, causing electric shock and/or fire.

True or false? The earth wire carries a current all the time the appliance is switched on.

False. The earth wire is at $0\ V$ and only carries a current if there is a fault.

True or false? Touching a live wire while standing on the ground can make your body part of a circuit.

True. You are at earth potential, so a current flows from the live wire through your body to earth.

What does the earth wire do if a fault makes the live wire touch the metal case of an appliance?

It carries the current safely to earth, so the case does not become live.