Practical Skills II: Planning (Edexcel International A Level (IAL) Physics): Flashcards
Exam code: YPH11
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Define resolution (of an instrument).
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Define resolution (of an instrument).
The resolution is the smallest increment an instrument can measure.
Define range (of an instrument).
The range is the highest and lowest value an instrument can measure.
Which instrument should be used to measure the diameter of a wire, and why?
A micrometer screw gauge, because it has the highest resolution for measuring very small lengths.
For an analogue instrument, such as a metre ruler or thermometer, how is the uncertainty in a single reading found?
The uncertainty is ± half the resolution of the instrument.
For a digital measuring device, the resolution gives its .......... uncertainty.
For a digital measuring device, the resolution gives its absolute uncertainty.
True or False?
The resolution of an instrument in an exam question can always be assumed from its typical value.
False.
Exam questions may give instruments with different resolutions (e.g. an ammeter of resolution 0.2 mA). Always use the resolution stated in the question rather than assuming a typical value.
Two digital thermometers read 80.13 °C and 42.0 °C. Which has the better resolution?
Thermometer 1 (80.13 °C), because its smallest increment is 0.01 °C compared with 0.1 °C for thermometer 2.
Define calibration.
Calibration is a comparison between a known measurement and the measurement obtained using an instrument, used to check the instrument's accuracy.
Define calibration curve.
A calibration curve is a graph used to convert readings from one measurement scale (e.g. e.m.f or resistance) to another (e.g. temperature), for instruments whose output is not proportional to the quantity measured.
Why should a voltmeter or ammeter be checked to read zero before measurements are taken?
To avoid a zero error, which would otherwise introduce a systematic error into every reading.
Give two examples of sensors that require a calibration curve, rather than a straight-line relationship, to convert their output.
A thermocouple (e.m.f against temperature) and a thermistor (resistance against temperature).
The accuracy of all measuring devices .......... over time, typically due to normal wear and tear.
The accuracy of all measuring devices degrades over time, typically due to normal wear and tear.
True or False?
A calibration curve that passes through the origin indicates the instrument has a systematic error.
False.
A curve passing through the origin (0,0) means the reading equals the true value. A systematic error is shown when the curve does NOT pass through the origin.
Define the use of a micrometer screw gauge.
A micrometer screw gauge is used to measure very short lengths, typically between 0.01 mm and 0.1 mm, such as the diameter of a wire.
Define the use of an oscilloscope.
An oscilloscope is used to display waves and measure their frequency, for example the frequency of a signal.
Which instrument should be used to measure the angle of refraction of a beam of light?
A protractor.
What is the key factor to consider when choosing the appropriate instrument to measure a variable?
The instrument's resolution — if it is too big (too coarse), it will not be able to measure small measurements accurately.
A .......... provides a monochromatic, coherent source of light, used to investigate the interference of light.
A laser provides a monochromatic, coherent source of light, used to investigate the interference of light.
True or False?
Vernier calipers are the most appropriate instrument for measuring the diameter of a thin wire.
False.
A wire's diameter is usually too small for vernier calipers (suited to 0.1 mm – 1 cm); a micrometer screw gauge (0.01 mm – 0.1 mm) should be used instead.
Define independent variable.
The independent variable is the only variable that should be deliberately changed throughout an experiment.
Define dependent variable.
The dependent variable is the variable that is measured to determine the outcome (results) of an experiment.
Define fair test.
A fair test is one in which only the independent variable is allowed to affect the dependent variable.
In an experiment investigating Charles' law, identify the independent, dependent and control variables.
Independent: temperature
Dependent: volume
Control: pressure and number of moles
Why is temperature commonly a control variable in circuit experiments (unless using a thermistor)?
Because the temperature of a wire or component rises as current flows over time, which would otherwise affect resistance and the results.
If control variables are not kept constant, the results of an experiment become ...........
If control variables are not kept constant, the results of an experiment become unreliable.
True or False?
More than one variable can be changed at a time, as long as the dependent variable is still measured accurately.
False.
Only the independent variable should be changed. Changing more than one variable at once means the test is no longer fair, since it would be unclear which change caused the effect.
Define anomalous result.
An anomalous result is a result that does not fit in with the pattern of the other readings.
Why are repeat readings taken in an experiment?
To improve the accuracy and reliability of a measurement, and to help identify any anomalous results.
How should the value of a repeated variable be used in further calculations?
The average (mean) of the repeat readings should be calculated and used.
Give an example of an experiment where taking repeat readings immediately, one after another, would not give a fair test.
An electrical circuit experiment, where components heat up during a reading and must be disconnected to cool before a genuine repeat can be taken. Repeating immediately would not be a fair test.
Repeat readings should be as .......... as possible, showing that the measurements were not simply the result of chance.
Repeat readings should be as precise as possible, showing that the measurements were not simply the result of chance.
True or False?
It is always best practice to repeat every reading in an experiment, however long that takes.
False.
Whether to repeat readings depends on how easy and quick this is. For experiments where conditions change between readings (e.g. heating components, or a time-dependent variable), full repeats may not be practical within the time available.
Why should the power supply be turned off between readings in an electrical circuit experiment?
To prevent components, especially thin wires, from overheating, which could cause a burn or affect results through a change in resistance due to temperature.
Why should safety goggles be worn when working with a wire under tension (e.g. in a Young modulus experiment)?
In case the wire snaps.
Why should liquids be kept away from electrical circuit apparatus?
Because a spill could cause a fire risk near the electrical equipment.
Why should a student stand up, rather than sit, for the duration of a practical?
So they can react quickly if something goes wrong with the apparatus.
A support stand should be .......... or weighted to prevent it from falling over.
A support stand should be clamped or weighted to prevent it from falling over.
True or False?
In the Edexcel International exam, it is enough to simply identify a safety hazard (e.g. "wires can become hot") to gain full marks on a "comment on safety" question.
False.
Full marks require both identifying the hazard AND explaining how it is dealt with, e.g. turning off the power supply between readings to let wires cool.
Define standard form.
Standard form is a way of writing very large or very small numbers as a value between 1 and 10 multiplied by a power of ten, e.g. the speed of light in a vacuum is 3.00 × 108 m s-1.
What rule applies to significant figures within a single column of data?
All values in a data column must be quoted to the same number of significant figures.
When calculating a mean value from repeat readings, how many extra significant figures is it acceptable to use?
It is acceptable to increase the number of significant figures by one compared with the raw readings.
What graph skills are expected when analysing practical data?
Finding the gradient and y-intercept of a straight-line graph of the form y = mx + c
Finding the area under a graph, including estimating areas under curves
Drawing tangents to a curve and calculating their gradient
Using and interpreting logarithmic plots
Understanding where asymptotes may be required
According to the .......... law, the intensity of gamma radiation from a point source is inversely proportional to the square of the distance from the source.
According to the inverse square law, the intensity of gamma radiation from a point source is inversely proportional to the square of the distance from the source.
True or False?
Plotting a graph of the corrected count rate, C, against distance, x, produces a straight line that confirms the inverse square law for gamma radiation.
False.
To confirm the inverse square law, a graph of C-1/2 against x must be plotted; a straight line through the origin on this graph (not a plot of C against x) confirms the inverse square relationship.
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