9702 · 10.3
Potential dividers flashcards
Revision flashcards for Cambridge 9702 Potential dividers (syllabus 10.3). Flip, recall, then mark a real past-paper question.
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What is the core function of a potential divider circuit?
To divide a supply voltage into smaller, desired output voltages.
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State the potential divider formula for Vₒᵤₜ across R₂ in series with R₁ and Vᵢₙ.
$$V_{out} = V_{in} \times \frac{R_2}{R_1 + R_2}$$
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How can a potential divider provide a continuously adjustable output voltage?
By using a variable resistor, such as a potentiometer or rheostat, as part of the series combination.
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Name two types of resistive sensors used in potential dividers.
Thermistors and Light Dependent Resistors (LDRs).
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Why are null measurements, with potentiometers, considered more accurate?
They involve no current flow through the measured component, preventing alteration of its conditions or potential difference.
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What is the relationship between current in series resistors within a potential divider?
The current is the same through every resistor in a series potential divider circuit.
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How does an LDR's resistance change with light intensity?
The resistance of an LDR decreases as light intensity increases.
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Describe the typical behaviour of an NTC thermistor.
Its resistance decreases as temperature increases.
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What is a potentiometer?
A three-terminal variable resistor often used as a potential divider for continuously adjustable output voltage.
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What is the purpose of a galvanometer in null measurements?
It detects when there is zero current flow (the null point), signifying equal potential differences.
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In a potential divider with a fixed resistor and an LDR, if the output is taken across the LDR, how does `V_out` change as the room gets darker?
As the room gets darker, the LDR's resistance increases. This increases its share of the total voltage, so `V_out` increases.
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In a potential divider with a fixed resistor and an NTC thermistor, if the output is taken across the thermistor, how does `V_out` change as it gets hotter?
As it gets hotter, the NTC thermistor's resistance decreases. This decreases its share of the total voltage, so `V_out` decreases.
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A potential divider has `V_in = 10V` and two equal resistors, `R1 = R2`. What is the output voltage across `R2`?
5V. When resistors are equal, the voltage is divided equally. $$V_{out} = 10V \times \frac{R}{R + R} = 10V \times \frac{R}{2R} = 10V \times 0.5 = 5V$$