OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(ii) techniques and procedures to investigate the charge and the discharge…
Full specification wording
Charging and discharging capacitors: (ii) techniques and procedures to investigate the charge and the discharge of a capacitor using both meters and data-loggers
To investigate charging and discharging, connect the capacitor, resistor and switch in series with a suitable supply, then measure either the current through the circuit or the potential…
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 2 of 6
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
To investigate charging and discharging, connect the capacitor, resistor and switch in series with a suitable supply, then measure either the current through the circuit or the potential difference across the capacitor. With meters, a voltmeter across the capacitor and an ammeter in series let you take readings at timed intervals, but manual timing is imprecise because the change is fast at the start. A data-logger with a voltage or current sensor records many readings per second automatically, giving smooth exponential graphs and allowing the time constant to be found from the curve. Choose a resistor and capacitor so τ = RC is long enough to observe, and use a sensor range that matches the expected voltages.
What earns the marks
- Describes a series circuit containing a capacitor, resistor, switch and supply for charging and discharging.
- States that a voltmeter is connected in parallel with the capacitor and an ammeter in series with the circuit.
- Explains that a data-logger records many readings automatically and produces a smooth graph.
- Identifies that manual meter readings at timed intervals are less precise because the initial change is rapid.
- Chooses component values so the time constant is long enough to measure, and selects a suitable sensor range.
Common mistakes and how to put them right
Connecting the voltmeter in series with the capacitor instead of in parallel.
Put it right: A voltmeter must be in parallel to measure potential difference.
Choosing a very small time constant so the capacitor discharges before readings can be taken.
Put it right: A larger resistor or capacitor slows the change.
Assuming a data-logger removes all error.
Put it right: The sensor range and sampling rate still affect the quality of the results.
Exam tips
- State clearly where each meter is connected and what quantity it measures.
- Explain one advantage of a data-logger, such as automatic recording of many readings or smooth graph plotting.
- Suggest a sensible check, such as repeating the experiment or using a longer time constant, to improve reliability.
Try the lesson
The start of the Charging and discharging capacitors: (ii) techniques and procedures to investigate the charge and the discharge of a capacitor using both meters and data-loggers lesson, made from checked teaching notes for this specification point.
Listen
To investigate charging and discharging, connect the capacitor, resistor and switch in series with a suitable supply, then measure either the current through the circuit or the potential difference across the capacitor. With meters, a voltmeter across the capacitor and an ammeter in series let you take readings at timed intervals, but manual timing is imprecise because the change is fast at the start. A data-logger with a voltage or current sensor records many readings per second automatically, giving smooth exponential graphs and allowing the time constant to be found from the curve. Choose a resistor and capacitor so τ = RC is long enough to observe, and use a sensor range that matches the expected voltages. A strong answer earns marks for these points. Describes a series circuit containing a capacitor, resistor, switch and supply for charging and discharging. States that a voltmeter is connected in parallel with the capacitor and an ammeter in series with the circuit. Explains that a data-logger records many readings automatically and produces a smooth graph. Identifies that manual meter readings at timed intervals are less precise because the initial change is rapid. Exam tip: State clearly where each meter is connected and what quantity it measures.
Key words
Say what each word means before you turn the card.
Circuit setup for capacitor investigations
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Time constant and component choice
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Graph plotting and analysis
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See every definition
- Circuit setup for capacitor investigations
- The capacitor, resistor and switch are connected in series with a suitable supply, and either the current through the circuit or the potential difference across the capacitor is measured.
- Time constant and component choice
- A resistor and capacitor are chosen so that τ = RC is long enough to observe.
- Graph plotting and analysis
- A data-logger gives smooth exponential graphs and allows the time constant to be found from the curve.
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