Circuits Flashcards – AQA A-level Physics (7408)

When are resistors connected in series?

When they lie on the same unbranched path.

How does the current compare through resistors in series?

The same current passes through each resistor.

How does the total potential difference across resistors in series relate to the potential differences across them?

It is the sum of the potential differences across the individual resistors.

For resistors carrying the same current, how does the potential difference across each relate to its resistance?

The potential difference is proportional to its resistance.

What is the total resistance of resistors in series?

$R_T = R_1 + R_2 + R_3 + \ldots$

What happens to the total resistance when a resistor is added in series?

The total resistance increases.

When are resistors connected in parallel?

When each resistor is connected across the same two circuit points.

How does the potential difference compare across branches of a parallel resistor circuit?

It is the same across each branch.

How is the total current entering a parallel resistor combination related to the branch currents?

It equals the sum of the branch currents.

For a given potential difference, how does branch resistance affect current in a parallel resistor circuit?

A branch with lower resistance carries a greater current.

What equation gives the total resistance of resistors in parallel?

$\frac{1}{R_T} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldots$

How does the total resistance of parallel resistors compare with the resistance of each branch?

It is less than the resistance of any individual branch.

How do the voltages of cells in series combine when their orientations aid or oppose one another?

They add when the orientations aid one another and subtract when they oppose one another.

What potential difference do identical cells connected in parallel with the same polarity provide?

The same potential difference as one cell, not the sum of their voltages.

How is the current supplied to a circuit shared by cells connected in parallel?

The cells share the current supplied to the circuit.

How does the time for which parallel cells can supply current compare with that of a single cell?

Parallel cells can supply current for longer than a single cell.

What is electrical power?

The rate of energy transfer.

What is the electrical power of a component in terms of the current through it and potential difference across it?

$P = IV$

How much energy is transferred when current and potential difference remain constant for a time $t$?

$E = IVt$

For a resistor obeying $V = IR$, what are the two expressions for power in terms of resistance?

$P = I^2R = \frac{V^2}{R}$

What is the unit of energy $E$?

The joule (J).

What is the unit of power $P$?

The watt (W).

What is the unit of current $I$?

The ampere (A).

What is the unit of potential difference $V$?

The volt (V).

What is the unit of resistance $R$?

The ohm ($\Omega$).

What is the unit of time $t$ in the electrical energy equation?

The second (s).

What does conservation of charge mean for components in a dc circuit?

Components do not use up electric charge.

What is electric current?

The rate of flow of charge.

How are currents related at a junction where charge does not accumulate?

The total current entering equals the total current leaving.

How does current vary along an unbranched section of a circuit?

It is the same throughout the section.

What can happen to current at branches in a circuit?

It can divide between branches and recombine.

What roles do cells and other components play in energy transfer in a DC circuit?

Cells transfer energy to charges; other components transfer energy from the circuit to other energy stores or the surroundings.

What is potential difference?

The energy transferred per unit charge.

How are voltage rises and drops related around a complete circuit loop?

The total voltage rises equal the total voltage drops: energy supplied per unit charge equals energy transferred per unit charge by the other components.