Define electric current .

Electric current is the rate of flow of charge , measured in amperes (A) .

True or False? Conventional current flows in the same direction as electron flow in a wire.

False. Conventional current flows from the positive terminal to the negative terminal, which is opposite to the direction electrons actually flow.

How should an ammeter be connected in a circuit, and why?

An ammeter is connected in series with the component, because the current is the same at all points in a series circuit.

Electric current is the rate of flow of .......... .

Electric current is the rate of flow of charge .

Define potential difference .

Potential difference is the work done per unit charge , measured in volts (V) .

How is potential difference measured, and how must the meter be connected?

Potential difference is measured with a voltmeter , connected in parallel across (i.e. between two points of) the component.

True or False? The potential difference across two components connected in parallel is always the same.

True. This follows from conservation of energy — components in parallel share the same two connection points, so the pd across each is equal.

Potential difference is defined as the .......... done per unit charge.

Potential difference is defined as the work done per unit charge.

The current through a component is directly proportional to the potential difference across it, provided the temperature (and hence resistance) is constant.

How can you tell from a current−potential difference graph whether a component obeys Ohm's law?

The graph is a straight line through the origin . If the graph curves, the component does not obey Ohm's law.

What is one ohm defined as?

One ohm is defined as one volt per ampere .

True or False? A filament lamp obeys Ohm's law.

False. A filament lamp's resistance increases as it heats up, so its current is not directly proportional to the pd across it — its I–V graph curves.

The resistance of a component can be found from its current−potential difference graph using R = .......... of the graph.

The resistance of a component can be found from its current−potential difference graph using R = 1 ÷ gradient of the graph.

Define the electric current rule (Kirchhoff's first law).

The algebraic sum of the currents entering and leaving a junction is zero — a consequence of the conservation of charge.

Define a junction in a circuit.

A point where at least three circuit paths meet.

In a series circuit, how does the current compare at different points?

The current is the same at every point in a series circuit.

True or False? When current reaches a junction and splits into two branches, the total current after the split is greater than before.

False. Charge is conserved, so the sum of the currents leaving a junction equals the current entering it — it does not increase.

A .......... is a path connecting two junctions in a circuit.

A branch is a path connecting two junctions in a circuit.

Define the electrical voltages rule (Kirchhoff's second law).

In any closed circuit loop, the sum of the e.m.f.s is equal to the sum of the potential differences .

In a series circuit, how does the sum of the potential differences across the components compare to the e.m.f. of the supply?

It is equal to the total e.m.f. of the power supply, since the voltage is split across the components.

Why can each closed loop in a parallel circuit be treated as an independent series circuit?

Because each loop separates at a junction, and the sum of the pds in that loop equals the total e.m.f. of the source — the same relationship as in a series circuit.

True or False? In a parallel circuit, if one branch (e.g. a light) breaks, current stops flowing in all the other branches too.

False. Each loop in a parallel circuit is independent, so current can still flow through the other branches even if one breaks — this is why parallel circuits are used for home wiring.

In a parallel circuit, the potential difference is the same across each closed .......... .

In a parallel circuit, the potential difference is the same across each closed loop .

In a series circuit, how are current and potential difference distributed among the resistors?

The current is the same through all resistors; the potential difference is split between them.

In a parallel circuit, how are current and potential difference distributed among the resistors?

The potential difference is the same across all resistors; the current splits between them.

True or False? The combined resistance of two resistors in parallel is greater than the resistance of either individual resistor.

False. Adding a parallel path gives current more routes to flow, so the combined resistance is always less than the smallest individual resistance.

Two identical resistors are connected in parallel. How does their combined resistance compare to the resistance of one resistor?

It halves . For example, two 10 Ω resistors in parallel give a combined resistance of 5 Ω.

When resistors are connected in parallel, the combined resistance is always .......... than the resistance of the smallest individual resistor.

When resistors are connected in parallel, the combined resistance is always less than the resistance of the smallest individual resistor.

Define electrical power .

The rate at which work is done (energy is transferred) by a component in a circuit

For a fixed resistance, doubling the potential difference across a component increases the power dissipated by a factor of .......... .

For a fixed resistance, doubling the potential difference across a component increases the power dissipated by a factor of four .

Define ohmic conductor .

A component whose I–V graph is a straight line through the origin, showing that current is directly proportional to potential difference at constant temperature

Describe the shape of the I–V graph for a filament lamp.

An 'S' shaped curve The gradient decreases as the current increases Straight near the origin, then curves as current increases

Describe the shape of the I–V graph for a thermistor.

A shallow curve that gets steeper as current increases The gradient increases with increasing current

Explain why the resistance of a filament lamp increases as the current through it increases.

The increasing current raises the temperature of the filament Since the filament is a metal, the higher temperature causes an increase in resistance This resistance opposes the current, causing it to increase at a slower rate than the potential difference

For an ohmic conductor at constant temperature, current is .......... proportional to potential difference.

For an ohmic conductor at constant temperature, current is directly proportional to potential difference.

True or False? A filament lamp obeys Ohm's law across its entire range of operation.

False. A filament lamp only obeys Ohm's law at small voltages/currents. At higher currents, the rising temperature increases resistance, curving the I–V graph

International A Level (IAL)PhysicsEdexcelFlashcards2. Waves & ElectricityCurrent, Potential Difference, Resistance & Power

Current, Potential Difference, Resistance & Power (Edexcel International A Level (IAL) Physics): Flashcards

Exam code: YPH11

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Define electric current.

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Cards in this collection (51)

Define electric current.
Electric current is the rate of flow of charge, measured in amperes (A).
What equation links charge, current and time?
$Q = I t$
What equation links charge to the number of charge carriers?
$Q = n e$
where n is the number of electrons and e is the charge on one electron (1.6 × 10^-19 C).
True or False?
Conventional current flows in the same direction as electron flow in a wire.
False.
Conventional current flows from the positive terminal to the negative terminal, which is opposite to the direction electrons actually flow.
How should an ammeter be connected in a circuit, and why?
An ammeter is connected in series with the component, because the current is the same at all points in a series circuit.
Electric current is the rate of flow of ...........
Electric current is the rate of flow of charge.
Define potential difference.
Potential difference is the work done per unit charge, measured in volts (V).
What equation relates potential difference, work done and charge?
$V = \frac{W}{Q}$
How is potential difference measured, and how must the meter be connected?
Potential difference is measured with a voltmeter, connected in parallel across (i.e. between two points of) the component.
True or False?
The potential difference across two components connected in parallel is always the same.
True.
This follows from conservation of energy — components in parallel share the same two connection points, so the pd across each is equal.
A charge of 4 C passes through a resistor connected to a 6 V supply. Calculate the work done.
$W = V Q = 6 \times 4 = 24 J$
Potential difference is defined as the .......... done per unit charge.
Potential difference is defined as the work done per unit charge.
Define resistance.
Resistance is the opposition to current, defined as $R = \frac{V}{I}$ , and measured in ohms (Ω).
Define Ohm's law.
The current through a component is directly proportional to the potential difference across it, provided the temperature (and hence resistance) is constant.
How can you tell from a current−potential difference graph whether a component obeys Ohm's law?
The graph is a straight line through the origin. If the graph curves, the component does not obey Ohm's law.
What is one ohm defined as?
One ohm is defined as one volt per ampere.
True or False?
A filament lamp obeys Ohm's law.
False.
A filament lamp's resistance increases as it heats up, so its current is not directly proportional to the pd across it — its I–V graph curves.
The resistance of a component can be found from its current−potential difference graph using R = .......... of the graph.
The resistance of a component can be found from its current−potential difference graph using R = 1 ÷ gradient of the graph.
Define the electric current rule (Kirchhoff's first law).
The algebraic sum of the currents entering and leaving a junction is zero — a consequence of the conservation of charge.
Define a junction in a circuit.
A point where at least three circuit paths meet.
In a series circuit, how does the current compare at different points?
The current is the same at every point in a series circuit.
A current of 6 A enters a junction and splits into three branches. Two of the branches carry 2 A and 1 A. What is the current in the third branch?
3 A, since $6 = 2 + 1 + I_{3}$ , so $I_{3} = 3 A$
True or False?
When current reaches a junction and splits into two branches, the total current after the split is greater than before.
False.
Charge is conserved, so the sum of the currents leaving a junction equals the current entering it — it does not increase.
A .......... is a path connecting two junctions in a circuit.
A branch is a path connecting two junctions in a circuit.
Define the electrical voltages rule (Kirchhoff's second law).
In any closed circuit loop, the sum of the e.m.f.s is equal to the sum of the potential differences.
In a series circuit, how does the sum of the potential differences across the components compare to the e.m.f. of the supply?
It is equal to the total e.m.f. of the power supply, since the voltage is split across the components.
Why can each closed loop in a parallel circuit be treated as an independent series circuit?
Because each loop separates at a junction, and the sum of the pds in that loop equals the total e.m.f. of the source — the same relationship as in a series circuit.
For a loop containing two cells (e.m.f. E₁ and E₂) and two resistors (pd V₁ and V₂), write the equation given by the electrical voltages rule.
$E_{1} + E_{2} = V_{1} + V_{2}$
True or False?
In a parallel circuit, if one branch (e.g. a light) breaks, current stops flowing in all the other branches too.
False.
Each loop in a parallel circuit is independent, so current can still flow through the other branches even if one breaks — this is why parallel circuits are used for home wiring.
In a parallel circuit, the potential difference is the same across each closed ...........
In a parallel circuit, the potential difference is the same across each closed loop.
Define how resistors in series combine.
$R_{T} = R_{1} + R_{2} + . . .$
The combined resistance equals the sum of the individual resistances.
Define how resistors in parallel combine.
$\frac{1}{R_{T}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + . . .$
The reciprocal of the combined resistance equals the sum of the reciprocals of the individual resistances.
In a series circuit, how are current and potential difference distributed among the resistors?
The current is the same through all resistors; the potential difference is split between them.
In a parallel circuit, how are current and potential difference distributed among the resistors?
The potential difference is the same across all resistors; the current splits between them.
True or False?
The combined resistance of two resistors in parallel is greater than the resistance of either individual resistor.
False.
Adding a parallel path gives current more routes to flow, so the combined resistance is always less than the smallest individual resistance.
Two identical resistors are connected in parallel. How does their combined resistance compare to the resistance of one resistor?
It halves. For example, two 10 Ω resistors in parallel give a combined resistance of 5 Ω.
When resistors are connected in parallel, the combined resistance is always .......... than the resistance of the smallest individual resistor.
When resistors are connected in parallel, the combined resistance is always less than the resistance of the smallest individual resistor.
Define electrical power.
The rate at which work is done (energy is transferred) by a component in a circuit
Define potential difference.
The work done per unit charge transferred between two points in a circuit
$V = \frac{W}{Q}$
State the equation for electrical power in terms of potential difference and current.
$P = V I$
State the equation for electrical power in terms of current and resistance.
$P = I^{2} R$
State the equation for electrical power in terms of potential difference and resistance.
$P = \frac{V^{2}}{R}$
For a fixed resistance, doubling the potential difference across a component increases the power dissipated by a factor of ...........
For a fixed resistance, doubling the potential difference across a component increases the power dissipated by a factor of four.
True or False?
Doubling the current through a fixed resistance doubles the power dissipated.
False.
Since $P = I^{2} R$ , doubling the current increases the power dissipated by a factor of four, not two
Define ohmic conductor.
A component whose I–V graph is a straight line through the origin, showing that current is directly proportional to potential difference at constant temperature
Describe the shape of the I–V graph for a filament lamp.
- An 'S' shaped curve
- The gradient decreases as the current increases
- Straight near the origin, then curves as current increases
Describe the shape of the I–V graph for a thermistor.
- A shallow curve that gets steeper as current increases
- The gradient increases with increasing current
Explain why the resistance of a filament lamp increases as the current through it increases.
- The increasing current raises the temperature of the filament
- Since the filament is a metal, the higher temperature causes an increase in resistance
- This resistance opposes the current, causing it to increase at a slower rate than the potential difference
State the typical threshold voltage at which a semiconductor diode begins to conduct in forward bias.
Around 0.6 V
For an ohmic conductor at constant temperature, current is .......... proportional to potential difference.
For an ohmic conductor at constant temperature, current is directly proportional to potential difference.
True or False?
A filament lamp obeys Ohm's law across its entire range of operation.
False.
A filament lamp only obeys Ohm's law at small voltages/currents. At higher currents, the rising temperature increases resistance, curving the I–V graph

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