I-V Characteristics

Q1 If an I-V graph is a straight line through the origin, what does this tell you about the resistance?

Answer: The resistance is constant and ohmic, meaning it does not change with voltage or current.

Q2 Draw an I-V characteristic graph for a resistor?

The graph will be a straight line passing through the origin, indicating a constant resistance.

Q3 What is an LDR?

An LDR (Light Dependent Resistor) is a type of resistor whose resistance changes with the intensity of light falling on it.

Q4 Draw an I-V characteristic graph for a diode. Label the areas of forward bias and reverse bias.

The graph will show a sharp increase in current in the forward bias region and almost no current in the reverse bias region.

Q1a) What type of graph represents the current-voltage relationship for a filament lamp?

Q1b) How does increasing the voltage across a filament lamp impact its resistance in relation to the mean drift velocity of electrons in the lamp?

The mean drift velocity of electrons also increases with higher voltage, contributing to the rise in resistance.

Q1c) How does the resistance of an NTC thermistor change with temperature?

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What does the term 'I-V characteristic' refer to?

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A graph showing how the current changes as the potential difference across a component is increased.

How can you investigate the I-V characteristic of a component using a test circuit?

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By using a variable resistor to alter the potential difference across the component, recording V and I, repeating measurements, taking averages, and plotting a graph of current against potential difference.

What does the I-V Characteristic for a Metallic Conductor being a straight line indicate?

The resistance doesn’t change, it is equal to 1/gradient.

What does the shallower gradient of the I-V graph for a metallic conductor indicate?

The greater the resistance of the conductor.

Are metallic conductors ohmic?

Yes, they have constant resistance provided their temperature doesn’t change.

What is the characteristic graph for a filament lamp?

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A curve that starts steep but gets shallower as the potential difference rises.

Why does the resistance of a filament lamp increase as current flows through it?

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The current flowing through the lamp increases its temperature, leading to an increase in resistance.

How does the resistivity of a metal change with temperature?

Increases

How is charge carried through metals?

By free electrons in a lattice of positive ions

What effect does heating a metal have on the movement of electrons?

Makes it harder for electrons to move about

Why does the resistivity of a metal increase with temperature?

Due to increased collisions between electrons and vibrating positive ions

How does the decrease in kinetic energy affect the current in a wire?

Decreases the mean drift velocity and current in the wire

Why do semiconductors have higher resistivity than metals?

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Semiconductors have higher resistivity than metals because there are fewer charge carriers available.

How does increasing the temperature affect the resistance and resistivity of some semiconductors?

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Increasing the temperature of some semiconductors releases more charge carriers, leading to a decrease in resistance and resistivity.

What makes semiconductors excellent sensors for detecting changes in their environment?

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Semiconductors can detect changes in their environment due to the release of more charge carriers when energy is supplied, altering their resistance and resistivity.

Name three semiconductor components used as sensors

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Thermistors, LDRs (Light Dependent Resistors), and diodes are three semiconductor components commonly used as sensors.

What does the resistance of a thermistor depend on?

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The resistance of a thermistor depends on its temperature.

What does NTC stand for in the context of thermistors?

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NTC stands for ‘Negative Temperature Coefficient’.

How does the resistance of an NTC thermistor change with temperature?

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The resistance of an NTC thermistor decreases as the temperature goes up.

What does the characteristic I-V graph for an NTC thermistor show?

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As the voltage increases, the current increases, leading to a decrease in resistance.

How does warming the thermistor affect its resistance?

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Warming the thermistor gives more electrons enough energy to escape from their atoms, increasing charge carriers, current, and decreasing resistance.

What does LDR stand for in the context of resistors?

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LDR stands for Light-Dependent Resistor.

How does the resistance of an LDR change with light intensity?

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The resistance of an LDR decreases with an increase in light intensity.

How does light affect the resistance of an LDR?

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Light provides energy that releases more electrons, leading to more charge carriers, higher current, and lower resistance.

What is the main function of diodes?

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Diodes only let current flow in one direction.

What is forward bias in diodes?

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Forward bias is the direction in which the current is allowed to flow.

What threshold voltage is typically required for diodes to conduct in the forward direction?

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Most diodes require a threshold voltage of about 0.6V in the forward direction.

What happens to the resistance and current flow in a diode under reverse bias?

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In reverse bias, the resistance of the diode is very high and the current that flows is very tiny.