What happens to the combined resistance of a parallel circuit as more resistors are added?

It decreases , and is always less than the resistance of the smallest individual component.

Two resistors of equal resistance are connected in parallel. What happens to the combined resistance compared to a single resistor?

The combined resistance halves .

In a parallel circuit, the reciprocal of the combined resistance is the sum of the .......... of the individual resistances.

In a parallel circuit, the reciprocal of the combined resistance is the sum of the reciprocals of the individual resistances.

Define junction (in a circuit).

A junction is a point where at least three circuit paths meet.

Define Kirchhoff's First Law .

The sum of the currents entering a junction equals the sum of the currents leaving the junction (conservation of charge ).

Define Kirchhoff's Second Law .

The total e.m.f in a closed circuit equals the sum of the potential differences across each component (conservation of energy ).

How does current behave in a series circuit compared with a parallel circuit?

In series, current is the same through all components In parallel, current splits across branches, depending on each branch's resistance

Two cells are connected in series . How is the total voltage found?

The total voltage is the sum of the potential difference across each cell.

When cells are connected in .......... , the total voltage across the arrangement is the same as for one cell.

When cells are connected in parallel , the total voltage across the arrangement is the same as for one cell.

True or False? In a parallel circuit, the current is the same in every branch.

False. Current splits at each junction in a parallel circuit; the amount in each branch depends on that branch's resistance, though the total current in always equals the total current out (Kirchhoff's First Law).

When doing calculations involving electrical power, the unit is watts, so time must always be in .......... .

When doing calculations involving electrical power, the unit is watts, so time must always be in seconds .

Define a potential divider .

A circuit that produces an output voltage as a fraction of its input voltage, using two or more resistors in series.

How does the resistance of a light-dependent resistor (LDR) change with light intensity?

As light intensity increases , the resistance of the LDR decreases , and vice versa.

How does the resistance of a thermistor change with temperature?

As temperature increases , the resistance of the thermistor decreases , and vice versa.

Give two devices that commonly use a thermistor in a potential divider circuit.

Fire alarms Ovens Digital thermometers

In the potential divider equation, the numerator must be the resistance of the resistor over .......... .

In the potential divider equation, the numerator must be the resistance of the resistor over V\_out .

A LevelPhysicsAQAFlashcardsElectricityCircuits & The Potential Divider

Circuits & The Potential Divider (AQA A Level Physics): Flashcards

Exam code: 7408

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FrontResistors in Series & Parallel
What is the total resistance of resistors connected in series?

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Cards in this collection (26)

What is the total resistance of resistors connected in series?
The combined resistance equals the sum of the individual resistances:
$R_{T} = R_{1} + R_{2} + . . .$
What is the total resistance of resistors connected in parallel?
$\frac{1}{R_{T}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + . . .$
What happens to the combined resistance of a parallel circuit as more resistors are added?
It decreases, and is always less than the resistance of the smallest individual component.
Two resistors of equal resistance are connected in parallel. What happens to the combined resistance compared to a single resistor?
The combined resistance halves.
In a parallel circuit, the reciprocal of the combined resistance is the sum of the .......... of the individual resistances.
In a parallel circuit, the reciprocal of the combined resistance is the sum of the reciprocals of the individual resistances.
True or False?
When resistors are in parallel, you calculate $1 / R_{T}$ and this value is the total resistance.
False.
A common mistake is forgetting to take the reciprocal of $1 / R_{T}$ . Once you calculate $1 / R_{T}$ , you must invert it (1 ÷ your answer) to find $R_{T}$ .
Define junction (in a circuit).
A junction is a point where at least three circuit paths meet.
Define Kirchhoff's First Law.
The sum of the currents entering a junction equals the sum of the currents leaving the junction (conservation of charge).
Define Kirchhoff's Second Law.
The total e.m.f in a closed circuit equals the sum of the potential differences across each component (conservation of energy).
How does current behave in a series circuit compared with a parallel circuit?
- In series, current is the same through all components
- In parallel, current splits across branches, depending on each branch's resistance
Two cells are connected in series. How is the total voltage found?
The total voltage is the sum of the potential difference across each cell.
When cells are connected in .........., the total voltage across the arrangement is the same as for one cell.
When cells are connected in parallel, the total voltage across the arrangement is the same as for one cell.
True or False?
In a parallel circuit, the current is the same in every branch.
False.
Current splits at each junction in a parallel circuit; the amount in each branch depends on that branch's resistance, though the total current in always equals the total current out (Kirchhoff's First Law).
Define electrical power.
Electrical power is the rate of transfer of energy (work done per second) in a component:
$P = V I$
Write the two equations for electrical power in terms of resistance, R.
- $P = I^{2} R$
- $P = \frac{V^{2}}{R}$
For a fixed resistor, the current through it doubles. By what factor does the power dissipated change?
The power increases by a factor of four, since $P = I^{2} R$ .
Write the equation for the electrical energy transferred, E, in terms of voltage, current and time.
$E = V I t$
When doing calculations involving electrical power, the unit is watts, so time must always be in ...........
When doing calculations involving electrical power, the unit is watts, so time must always be in seconds.
True or False?
Doubling the voltage across a fixed resistor doubles the power dissipated in it.
False.
Since $P = \frac{V^{2}}{R}$ , doubling the voltage quadruples the power dissipated.
Define a potential divider.
A circuit that produces an output voltage as a fraction of its input voltage, using two or more resistors in series.
Write the potential divider equation for $V_{o u t}$ across resistor $R_{2}$ .
$V_{o u t} = \frac{R_{2}}{R_{1} + R_{2}} V_{i n}$
How does the resistance of a light-dependent resistor (LDR) change with light intensity?
As light intensity increases, the resistance of the LDR decreases, and vice versa.
How does the resistance of a thermistor change with temperature?
As temperature increases, the resistance of the thermistor decreases, and vice versa.
Give two devices that commonly use a thermistor in a potential divider circuit.
- Fire alarms
- Ovens
- Digital thermometers
In the potential divider equation, the numerator must be the resistance of the resistor over ...........
In the potential divider equation, the numerator must be the resistance of the resistor over V\_out.
True or False?
In a potential divider circuit, the potential difference across a resistor is inversely proportional to its resistance.
False.
From $V = I R$ , since the same current flows through both resistors, the potential difference across a resistor is directly proportional to its resistance — the resistor with the largest resistance has the greatest share of the potential difference.

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