Define electric current .

The rate of flow of charge Measured in amperes (A) , or amps

Define electric charge .

A property of some particles, measured in coulombs (C) Protons carry positive charge and electrons carry negative charge

In electrical wires the charge carriers are .......... , which flow from the .......... terminal towards the .......... terminal of a cell

In electrical wires the charge carriers are electrons , which flow from the negative terminal towards the positive terminal of a cell

True or False? Conventional current is the flow of electrons

False. Conventional current is the flow of positive charge, from the positive terminal to the negative terminal of a cell — the opposite direction to electron flow

How should an ammeter be connected to measure current, and why?

In series with the component The current is the same at all points in a series circuit

Define potential difference .

The work done per unit charge between two points Measured in volts (V) , and sometimes called the voltage

A voltmeter is always connected in .......... with (or 'across') the component being measured

A voltmeter is always connected in parallel with (or 'across') the component being measured

True or False? Potential difference is measured in amperes

False. Potential difference is measured in volts (V) . The ampere is the unit of current

Why is the potential difference the same across components connected in parallel?

Because of conservation of energy

What is the unit of resistance, and how is it defined?

The ohm (Ω) One ohm is defined as one volt per ampere

The current through a component is directly proportional to the potential difference across it, provided the temperature is constant

A component obeys Ohm's law if its graph of current against potential difference is a .......... through the ..........

A component obeys Ohm's law if its graph of current against potential difference is a straight line through the origin

How can resistance be found from a current–potential difference graph?

Resistance = 1 ÷ gradient of the graph

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

False. A filament lamp does not obey Ohm's law — its current–pd graph is not a straight line through the origin. A fixed resistor does obey Ohm's law

Does reducing the current in a circuit cause the resistance to increase?

No. It is the other way round — increasing the resistance reduces the current. Resistance controls the size of the current, not the reverse

In an experiment to measure resistance, how are the meters arranged and what voltage is used?

Ammeter in series with the component Voltmeter in parallel across the component Use a low voltage (1–2 V) to avoid heating the component

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

The algebraic sum of the currents entering and leaving a junction is equal to zero

The electric current rule is a consequence of which conservation law?

Conservation of charge Current does not decrease or increase when a circuit splits

A .......... is a point where at least three circuit paths meet, while a .......... is a path connecting two junctions

A junction is a point where at least three circuit paths meet, while a branch is a path connecting two junctions

What can be said about the current at all points in a series circuit?

The current is the same at every point

True or False? Current is used up as it passes through a junction

False. Charge is conserved — the total current flowing into a junction equals the total current flowing out of it

What happens to the current at each junction in a parallel circuit?

The current divides at each junction, so each branch may carry a different value The sum of the currents into a junction equals the sum of the currents out

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

The sum of the e.m.f.s in a closed circuit loop is equal to the sum of the potential differences around that loop.

Which conservation law does the electrical voltages rule follow from?

The law of conservation of energy — energy is never used up or lost in a circuit.

In a series circuit, the sum of the voltages across the components is equal to the total .......... of the power supply.

In a series circuit, the sum of the voltages across the components is equal to the total e.m.f. of the power supply.

In a parallel circuit, how does the sum of the potential differences in each closed loop compare with the total e.m.f. of the power supply?

It is equal to the total e.m.f. of the power supply. Each closed loop acts as its own independent series circuit , separating at a junction.

True or False? Electrical energy is used up as it flows around a circuit.

False. Energy is transferred to other stores when components do work, but it is never used up or lost — the total energy is conserved .

Why are parallel circuits useful for home wiring systems?

A single power source supplies every appliance with the same voltage , and if one component breaks, current and voltage can still flow through the remaining loops .

In a series circuit the current is the .......... through every resistor, while the potential difference is .......... between them.

In a series circuit the current is the same through every resistor, while the potential difference is split between them.

In a parallel circuit, how do the current and potential difference behave across the resistors?

The current splits at the junction between the resistors, while the potential difference is the same across each resistor.

True or False? Adding a resistor in parallel increases the total resistance.

False. The combined resistance of a parallel combination is less than any individual resistor, so adding a parallel path decreases the total resistance.

Two resistors of equal resistance are connected in parallel. What is the combined resistance?

Half the resistance of one resistor.

Describe the shape of the I–V graph for an ohmic conductor at constant temperature.

A straight line through the origin — the current is directly proportional to the potential difference, so resistance is constant.

Define forward bias for a diode.

When the current is in the direction of the diode's arrowhead symbol , so the diode conducts — shown by the sharp increase in current above the threshold voltage (typically around 0.6 V).

Why does the I–V graph for a filament lamp curve, with current increasing at a proportionally slower rate than the potential difference?

As the current increases, the filament's temperature rises . Because it is a metal, the higher temperature increases its resistance , which opposes the current and makes it increase at a slower rate .

For a filament lamp, as the current increases the temperature of the filament rises, causing its .......... to increase.

For a filament lamp, as the current increases the temperature of the filament rises, causing its resistance to increase.

Describe the I–V graph for a semiconductor diode.

Under reverse bias the current is zero (flat line on the left), and under forward bias the current rises sharply once the threshold voltage (around 0.6 V) is reached.

True or False? A filament lamp is an ohmic component.

False. Its resistance increases as it heats up, so current is not directly proportional to potential difference — it only obeys Ohm's law at small voltages.

What happens to the resistance of a thermistor as its temperature rises?

Its resistance decreases , allowing even more current to flow. Because current is not proportional to potential difference, a thermistor does not obey Ohm's law.

A LevelPhysicsEdexcelFlashcards3. Electric CircuitsCurrent, Potential Difference, Resistance & Power

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

Exam code: 9PH0

1/54

0Still learning

Know0

FrontElectric Current
Define electric current.

Was this flashcard helpful?

Cards in this collection (54)

Define electric current.
The rate of flow of charge
Measured in amperes (A), or amps
Which equation relates charge, current and time?
$Δ Q = I Δ t$
Current is the charge transferred per unit time
Define electric charge.
A property of some particles, measured in coulombs (C)
Protons carry positive charge and electrons carry negative charge
In electrical wires the charge carriers are .........., which flow from the .......... terminal towards the .......... terminal of a cell
In electrical wires the charge carriers are electrons, which flow from the negative terminal towards the positive terminal of a cell
True or False?
Conventional current is the flow of electrons
False.
Conventional current is the flow of positive charge, from the positive terminal to the negative terminal of a cell — the opposite direction to electron flow
How should an ammeter be connected to measure current, and why?
In series with the component
The current is the same at all points in a series circuit
How many electrons make up 1 C of charge?
6.25 × 10¹⁸ electrons
Since one electron carries 1.6 × 10^-19 C, found using $Q = n e$
Define potential difference.
The work done per unit charge between two points
Measured in volts (V), and sometimes called the voltage
Which equation relates potential difference, work done and charge?
$V = \frac{W}{Q}$
Potential difference is the energy transferred per coulomb of charge
A voltmeter is always connected in .......... with (or 'across') the component being measured
A voltmeter is always connected in parallel with (or 'across') the component being measured
True or False?
Potential difference is measured in amperes
False.
Potential difference is measured in volts (V). The ampere is the unit of current
A resistor is connected across a potential difference of 10 V. Calculate the work done when a charge of 2 C passes through it.
$W = V Q = 10 \times 2 = 20 J$
Why is the potential difference the same across components connected in parallel?
Because of conservation of energy
Define resistance.
The opposition to current in a conductor
Given by the ratio of potential difference to current, $R = \frac{V}{I}$
What is the unit of resistance, and how is it defined?
The ohm (Ω)
One ohm is defined as one volt per ampere
State Ohm's law.
The current through a component is directly proportional to the potential difference across it, provided the temperature is constant
A component obeys Ohm's law if its graph of current against potential difference is a .......... through the ..........
A component obeys Ohm's law if its graph of current against potential difference is a straight line through the origin
How can resistance be found from a current–potential difference graph?
Resistance = 1 ÷ gradient of the graph
True or False?
A filament lamp obeys Ohm's law
False.
A filament lamp does not obey Ohm's law — its current–pd graph is not a straight line through the origin. A fixed resistor does obey Ohm's law
Does reducing the current in a circuit cause the resistance to increase?
No.
It is the other way round — increasing the resistance reduces the current. Resistance controls the size of the current, not the reverse
In an experiment to measure resistance, how are the meters arranged and what voltage is used?
Ammeter in series with the component
Voltmeter in parallel across the component
Use a low voltage (1–2 V) to avoid heating the component
Define the electric current rule (Kirchhoff's first law).
The algebraic sum of the currents entering and leaving a junction is equal to zero
The electric current rule is a consequence of which conservation law?
Conservation of charge
Current does not decrease or increase when a circuit splits
A .......... is a point where at least three circuit paths meet, while a .......... is a path connecting two junctions
A junction is a point where at least three circuit paths meet, while a branch is a path connecting two junctions
What can be said about the current at all points in a series circuit?
The current is the same at every point
True or False?
Current is used up as it passes through a junction
False.
Charge is conserved — the total current flowing into a junction equals the total current flowing out of it
What happens to the current at each junction in a parallel circuit?
The current divides at each junction, so each branch may carry a different value
The sum of the currents into a junction equals the sum of the currents out
Define the electrical voltages rule (Kirchhoff's second law).
The sum of the e.m.f.s in a closed circuit loop is equal to the sum of the potential differences around that loop.
Which conservation law does the electrical voltages rule follow from?
The law of conservation of energy — energy is never used up or lost in a circuit.
In a series circuit, the sum of the voltages across the components is equal to the total .......... of the power supply.
In a series circuit, the sum of the voltages across the components is equal to the total e.m.f. of the power supply.
In a parallel circuit, how does the sum of the potential differences in each closed loop compare with the total e.m.f. of the power supply?
It is equal to the total e.m.f. of the power supply.
Each closed loop acts as its own independent series circuit, separating at a junction.
True or False?
Electrical energy is used up as it flows around a circuit.
False.
Energy is transferred to other stores when components do work, but it is never used up or lost — the total energy is conserved.
Why are parallel circuits useful for home wiring systems?
A single power source supplies every appliance with the same voltage, and if one component breaks, current and voltage can still flow through the remaining loops.
Define the combined resistance of resistors in series.
The combined resistance is equal to the sum of the individual resistances.
$R_{T} = R_{1} + R_{2} + R_{3} + ...$
Write the equation for the combined resistance of resistors in parallel.
$\frac{1}{R_{T}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \frac{1}{R_{3}} + ...$
The reciprocal of the combined resistance equals the sum of the reciprocals of the individual resistances.
In a series circuit the current is the .......... through every resistor, while the potential difference is .......... between them.
In a series circuit the current is the same through every resistor, while the potential difference is split between them.
In a parallel circuit, how do the current and potential difference behave across the resistors?
The current splits at the junction between the resistors, while the potential difference is the same across each resistor.
True or False?
Adding a resistor in parallel increases the total resistance.
False.
The combined resistance of a parallel combination is less than any individual resistor, so adding a parallel path decreases the total resistance.
Two resistors of equal resistance are connected in parallel. What is the combined resistance?
Half the resistance of one resistor.
When calculating parallel resistance, what must you do after summing the reciprocals of the individual resistances?
Take the reciprocal of the answer (do $\frac{1}{answer}$ ) to obtain $R_{T}$ — a common mistake is stopping at $\frac{1}{R_{T}}$ .
Define power.
The rate of doing work.
$P = \frac{W}{t}$
Define potential difference.
The work done per unit charge.
$V = \frac{W}{Q}$
State the equation for electrical power in terms of current and potential difference.
$P = I V$
where P is power (W), I is current (A) and V is potential difference (V).
The work done by an electrical component is given by $W = V I t$ , where potential difference is the work done per unit ...........
The work done by an electrical component is given by $W = V I t$ , where potential difference is the work done per unit charge.
Write the two equations for electrical power expressed in terms of resistance.
$P = I^{2} R$
$P = \frac{V^{2}}{R}$
For a fixed resistance, what happens to the power dissipated if the current doubles?
The power quadruples, because $P = I^{2} R$ (power is proportional to current squared).
True or False?
Doubling the voltage doubles the power dissipated.
False.
For a fixed resistance $P = \frac{V^{2}}{R}$ , so power is proportional to voltage squared — doubling the voltage quadruples the power.
Describe the shape of the I–V graph for an ohmic conductor at constant temperature.
A straight line through the origin — the current is directly proportional to the potential difference, so resistance is constant.
Define forward bias for a diode.
When the current is in the direction of the diode's arrowhead symbol, so the diode conducts — shown by the sharp increase in current above the threshold voltage (typically around 0.6 V).
Why does the I–V graph for a filament lamp curve, with current increasing at a proportionally slower rate than the potential difference?
As the current increases, the filament's temperature rises. Because it is a metal, the higher temperature increases its resistance, which opposes the current and makes it increase at a slower rate.
For a filament lamp, as the current increases the temperature of the filament rises, causing its .......... to increase.
For a filament lamp, as the current increases the temperature of the filament rises, causing its resistance to increase.
Describe the I–V graph for a semiconductor diode.
Under reverse bias the current is zero (flat line on the left), and under forward bias the current rises sharply once the threshold voltage (around 0.6 V) is reached.
True or False?
A filament lamp is an ohmic component.
False.
Its resistance increases as it heats up, so current is not directly proportional to potential difference — it only obeys Ohm's law at small voltages.
What happens to the resistance of a thermistor as its temperature rises?
Its resistance decreases, allowing even more current to flow. Because current is not proportional to potential difference, a thermistor does not obey Ohm's law.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Work, Energy & PowerNext:Resistance, Resistivity & Potential Dividers