The opposition to current in a circuit.

One ohm is equivalent to one .......... per ampere.

One ohm is equivalent to one volt per ampere.

True or False? For a given potential difference, a higher resistance results in a larger current.

False. For a given potential difference, a higher resistance results in a smaller current.

Why is a low voltage supply (typically 1–2 V) used when measuring the resistance of a component?

To avoid heating the component, which could otherwise affect its resistance.

Why are wires often made from copper ?

Copper has a low electrical resistance , making it a good conductor.

For a conductor at constant temperature , the current through it is directly proportional to the potential difference across it.

What condition must hold for a conductor's resistance to stay constant?

Its temperature must remain constant

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

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

How can the resistance of a resistor be found from its current−potential difference graph?

Resistance = 1 ÷ gradient of the graph, since the graph is a straight line with a constant gradient

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

False. A filament lamp's resistance increases as it heats up, so its I - V graph is a curve rather than a straight line through the origin.

Define forward bias .

Forward bias is when a semiconductor diode is connected so that current flows in the direction of its arrowhead symbol, allowing current to flow through it.

Resistivity is a property of a material that describes the extent to which it opposes the flow of electric current through it; it depends only on temperature .

Define reverse bias .

Reverse bias is when a semiconductor diode is connected the opposite way to its arrowhead symbol, so that it does not conduct.

Describe the I - V graph for a metallic conductor, such as a resistor, at constant temperature.

A straight line through the origin, showing that current is directly proportional to potential difference

Why does a wire heat up when current flows through it?

Free electrons collide with the vibrating metal ions in the wire, transferring some of their kinetic energy to the ions; the faster the ions vibrate, the greater the temperature of the wire.

Why does the current in a filament lamp increase at a decreasing rate as potential difference increases?

The current heats the filament, increasing its temperature ; the higher temperature increases the filament's resistance , which then opposes further increase in current.

For a wire of fixed resistivity, how does doubling its length affect its resistance, and how does doubling its cross-sectional area affect its resistance?

Doubling the length doubles the resistance Doubling the cross-sectional area halves the resistance

As the current in a filament lamp increases, its temperature increases, causing an increase in .......... .

As the current in a filament lamp increases, its temperature increases, causing an increase in resistance .

Copper has a relatively .......... resistivity, making it an ideal material for use in electrical wires.

Copper has a relatively low resistivity, making it an ideal material for use in electrical wires.

True or False? In reverse bias, a semiconductor diode conducts a large current.

False. In reverse bias , the diode does not conduct, shown by a zero (or near-zero) reading of current on the I - V graph.

True or False? Resistivity depends on the length and cross-sectional area of a sample of material.

False. Resistivity is a property of the material itself, dependent only on temperature; it is resistance that depends on the length and cross-sectional area of a sample.

Define a light-dependent resistor (LDR) .

An LDR is a non-ohmic, sensory resistor whose resistance decreases as light intensity increases.

Define a thermistor .

A thermistor is a non-ohmic, sensory resistor whose resistance decreases as temperature increases.

Give examples of circuits that use an LDR as a light sensor.

Street lighting Garden lights (automatically switching on when it gets dark)

Give examples of devices that use a thermistor as a temperature sensor.

Ovens Fire alarms Digital thermometers

How does the resistance of an LDR in the dark compare with its resistance in bright light?

In the dark, an LDR's resistance is very large (millions of ohms); in bright light, it is much smaller (tens of ohms).

True or False? At a fixed light intensity, an LDR obeys Ohm's law.

True. At a constant light intensity, an LDR's resistance stays constant, so its current is directly proportional to potential difference, in line with Ohm's law.

A LevelPhysicsCambridge (CIE)Flashcards9. ElectricityResistance & Resistivity

Resistance & Resistivity (Cambridge (CIE) A Level Physics): Flashcards

Exam code: 9702

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Cards in this collection (30)

Define resistance.
The opposition to current in a circuit.
State the equation for resistance in terms of potential difference and current.
$R = \frac{V}{I}$
One ohm is equivalent to one .......... per ampere.
One ohm is equivalent to one volt per ampere.
True or False?
For a given potential difference, a higher resistance results in a larger current.
False.
For a given potential difference, a higher resistance results in a smaller current.
Why is a low voltage supply (typically 1–2 V) used when measuring the resistance of a component?
To avoid heating the component, which could otherwise affect its resistance.
Why are wires often made from copper?
Copper has a low electrical resistance, making it a good conductor.
Define Ohm's law.
For a conductor at constant temperature, the current through it is directly proportional to the potential difference across it.
What equation expresses Ohm's law, and what does each symbol represent?
$V = I R$
- V = potential difference (V)
- I = current (A)
- R = resistance (Ω)
What condition must hold for a conductor's resistance to stay constant?
Its temperature must remain constant
An electrical component obeys Ohm's law if its graph of current against potential difference is a .......... through the origin.
An electrical component obeys Ohm's law if its graph of current against potential difference is a straight line through the origin.
How can the resistance of a resistor be found from its current−potential difference graph?
Resistance = 1 ÷ gradient of the graph, since the graph is a straight line with a constant gradient
True or False?
A filament lamp obeys Ohm's law.
False.
A filament lamp's resistance increases as it heats up, so its I-V graph is a curve rather than a straight line through the origin.
Define forward bias.
Forward bias is when a semiconductor diode is connected so that current flows in the direction of its arrowhead symbol, allowing current to flow through it.
Define resistivity.
Resistivity is a property of a material that describes the extent to which it opposes the flow of electric current through it; it depends only on temperature.
Define reverse bias.
Reverse bias is when a semiconductor diode is connected the opposite way to its arrowhead symbol, so that it does not conduct.
What equation links resistance to resistivity, length and cross-sectional area, and what are the units of each quantity?
$R = \frac{ρ L}{A}$
- R = resistance (Ω)
- ρ = resistivity (Ω m)
- L = length (m)
- A = cross-sectional area (m²)
Describe the I-V graph for a metallic conductor, such as a resistor, at constant temperature.
A straight line through the origin, showing that current is directly proportional to potential difference
Why does a wire heat up when current flows through it?
Free electrons collide with the vibrating metal ions in the wire, transferring some of their kinetic energy to the ions; the faster the ions vibrate, the greater the temperature of the wire.
Why does the current in a filament lamp increase at a decreasing rate as potential difference increases?
The current heats the filament, increasing its temperature; the higher temperature increases the filament's resistance, which then opposes further increase in current.
For a wire of fixed resistivity, how does doubling its length affect its resistance, and how does doubling its cross-sectional area affect its resistance?
- Doubling the length doubles the resistance
- Doubling the cross-sectional area halves the resistance
As the current in a filament lamp increases, its temperature increases, causing an increase in ...........
As the current in a filament lamp increases, its temperature increases, causing an increase in resistance.
Copper has a relatively .......... resistivity, making it an ideal material for use in electrical wires.
Copper has a relatively low resistivity, making it an ideal material for use in electrical wires.
True or False?
In reverse bias, a semiconductor diode conducts a large current.
False.
In reverse bias, the diode does not conduct, shown by a zero (or near-zero) reading of current on the I-V graph.
True or False?
Resistivity depends on the length and cross-sectional area of a sample of material.
False.
Resistivity is a property of the material itself, dependent only on temperature; it is resistance that depends on the length and cross-sectional area of a sample.
Define a light-dependent resistor (LDR).
An LDR is a non-ohmic, sensory resistor whose resistance decreases as light intensity increases.
Define a thermistor.
A thermistor is a non-ohmic, sensory resistor whose resistance decreases as temperature increases.
Give examples of circuits that use an LDR as a light sensor.
- Street lighting
- Garden lights
(automatically switching on when it gets dark)
Give examples of devices that use a thermistor as a temperature sensor.
- Ovens
- Fire alarms
- Digital thermometers
How does the resistance of an LDR in the dark compare with its resistance in bright light?
In the dark, an LDR's resistance is very large (millions of ohms); in bright light, it is much smaller (tens of ohms).
True or False?
At a fixed light intensity, an LDR obeys Ohm's law.
True.
At a constant light intensity, an LDR's resistance stays constant, so its current is directly proportional to potential difference, in line with Ohm's law.

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