Anyone who takes Physics AS will know that although the topics you learn about are a big contribution to the final mark of the G492 exam, they only account for 60% of all the marks. The last 40% comes from something you can prepare for. You are giving a green paper entitled ‘AS GCE PHYSICS B (ADVANCING PHYSICS G492 Understanding Processes/Experimentation and Data Handling’. Within this booklet will be three random articles of which will come up in the Section C of your exam. You can prepare for 40% of your exam this easily. For this reason, here are some revision notes for the year June/May 2012 for the three articles called 1. Quality of Measurement, 2. Measuring the Planck constant using LEDS and 3. Cavendish: Measuring the Earth’s Density. Feel free to skip to the parts most relevant to you.
If you haven’t got the article, you can find it here
1. Quality of Measurement
- Qualities and limitations of measuring instruments (being digital and analogue ammeter).
- Resolution, sensitivity and zero error of the measuring instruments.
- Identifying the largest uncertainty.
- Ways to reduce the uncertainty.
- Zero error as a systematic error.
- Low resolution of 0.01 amps: more accurate.
- Generally better than the analogue ammeter.
- It is easier to read from the digital ammeter. However, when recording a current, it will likely flicker a lot making it hard to determine the value. As well as this, there is a chance of the sensor having a zero error.
- We need to take into account that the sensor may have a small resistance creating a systematic error.
- High resolution of 1 amp.
- Hard to read because needle can be read at different heights causing the value to look different when look at different places.
- There may be a zero error.
- Hard to determine to 1d.p let alone 2.
- There may again be a resistance.
2. Measuring the Planck constant using LEDs
- ‘what the difficulties are and how the data can be processed’ – What are the difficulties with this experiment? Think about variables in a laboratory that would effect this experiment such as background light, resistance in the circuit and uncertainties.
- The biggest uncertainty is with ‘consistently and accurately judging the voltage at which the LED strikes’. This is when the observer has to make the judgement when he sees light produced by the LED. To reduce this uncertainty, the LED is shielded with a small opaque paper tube to block background light. However, there is the uncertainty of the observer their self.
- ‘Plotting an appropriate graph of the data allows a value for the Planck constant to be determined’.The gradient of this graph will be the planck constant. Therefore, we know if we have done the experiment right by comparing the gradient to the true value of the planck constant (6.6×10-^34).
Cavendish: Measuring the Earth’s Density
- Range – The range for all 29 value is 970.
- Spread – You can work out the spread by halving the range. Therefore, it is plus or minus 485.
- Mean – From all 29 values, the mean is 5448.
- Outliers – Are there any outliers in the data? To work out if there are any outliers, you work out the values that are twice the spread from the mean.
Therefore, 2 X spread = 970. 5448 (mean) + 970 (2 times the spread) = 6418. 5448-970 = 4478.
- Range – highest value – lowest value.
- Spread – range / 2.
- Mean – sum of all values / number of values there are.
- Outliers – Mean plus or minus 2 X spread. If it falls within the values, it is not an outlier.
- Uncertainty – spread / mean.