OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(ii) techniques and procedures used to investigate the electrical…
Full specification wording
Resistance: (ii) techniques and procedures used to investigate the electrical characteristics for
To investigate a component's electrical characteristic, connect it in series with an ammeter and a variable d.c. supply, and connect a voltmeter in parallel with the component.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 4 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
To investigate a component's electrical characteristic, connect it in series with an ammeter and a variable d.c. supply, and connect a voltmeter in parallel with the component. Vary the p.d. in small steps, record current and p.d. pairs, then plot current against p.d. For reverse-bias measurements on a diode or LED, reverse the supply connections and keep the current small with a protective resistor. Use a potential divider or variable resistor to control the p.d. smoothly. Take repeat readings and average them to reduce random error, and avoid overheating the component by switching off between readings.
What earns the marks
- Ammeter in series with the component to measure current.
- Voltmeter in parallel with the component to measure potential difference.
- Variable d.c. supply or potential divider to change the p.d. in controlled steps.
- Protective resistor or current limit to prevent damage to diode, LED or filament lamp.
- Record multiple I–V pairs, repeat and average, then plot a graph of current against p.d.
Common mistakes and how to put them right
Connecting the ammeter in parallel with the component.
Put it right: The ammeter must be in series so that the component's current passes through it.
Connecting the voltmeter in series.
Put it right: The voltmeter must be in parallel with the component to measure the p.d. across it.
Forgetting to reverse the supply for reverse-bias readings.
Put it right: Reverse the connections to obtain negative p.d. and current values.
Exam tips
- Sketch the circuit clearly and label the ammeter, voltmeter, component and variable supply.
- State that you change the p.d. in small steps and record corresponding current values.
- Mention a protective resistor or limiting current when testing diodes and LEDs.
Try the lesson
The start of the Resistance: (ii) techniques and procedures used to investigate the electrical characteristics for lesson, made from checked teaching notes for this specification point.
Listen
To investigate a component's electrical characteristic, connect it in series with an ammeter and a variable d.c. supply, and connect a voltmeter in parallel with the component. Vary the p.d. in small steps, record current and p.d. pairs, then plot current against p.d. For reverse-bias measurements on a diode or LED, reverse the supply connections and keep the current small with a protective resistor. Use a potential divider or variable resistor to control the p.d. smoothly. Take repeat readings and average them to reduce random error, and avoid overheating the component by switching off between readings. A strong answer earns marks for these points. Ammeter in series with the component to measure current. Voltmeter in parallel with the component to measure potential difference. Variable d.c. supply or potential divider to change the p.d. in controlled steps. Protective resistor or current limit to prevent damage to diode, LED or filament lamp. A common slip: Connecting the ammeter in parallel with the component. Instead, the ammeter must be in series so that the component's current passes through it. Exam tip: Sketch the circuit clearly and label the ammeter, voltmeter, component and variable supply.
Key words
Say what each word means before you turn the card.
Circuit design for measurement
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Variable control of p.d.
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Data logging and graphing
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Component protection
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See every definition
- Circuit design for measurement
- Connect the component in series with an ammeter and a variable d.c. supply, and connect a voltmeter in parallel with the component.
- Variable control of p.d.
- Use a potential divider or variable resistor to control the p.d. smoothly, varying it in small steps.
- Data logging and graphing
- Record current and p.d. pairs, take repeat readings and average them to reduce random error, then plot current against p.d.
- Component protection
- Keep the current small with a protective resistor, and avoid overheating the component by switching off between readings.
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