AQA Physics AS/A-level Year 1
Fig 1 Viewing along the line of the two fiducial markers means that you always view from the same point and you are better able to judge the start and end of the oscillation. The fiducial markers should be placed in the centre of the oscillation, where the pendulum is moving at its highest speed.
Systematic errors may add a constant value to all the readings, or may have a multiplier effect, changing all the results by the same percentage.1 For example: • Using a meter or balance which is not zeroed correctly. This zero error will be added to each subsequent reading. • Misreading a scale due to poor alignment of the observer’s eye and the scale, often referred to as parallax error (see Fig 2). • Failing to take account of the resistance of the connections in an electrical circuit. • Using a poorly calibrated thermometer to measure the temperature of an object, or failing to make a good thermal contact between the thermometer and the object. Systematic errors reduce the accuracy of a measurement, so that it is further away from the actual value. In some cases, where the actual value is not known, it may be difficult to quantify, or even identify, systematic errors. However, systematic errors may come to light if the results are not reproducible: that is, they cannot be replicated by other experimenters, using different apparatus and possibly a different method.
Reducing systematic errors The effect of a systematic error cannot be reduced by repeating the readings, since the same error will affect all the readings in the same way. A change in the method is required. Examples that occur in A and AS-level experiments include: • Parallax errors. These occur when measurements are taken from an analogue meter or a scale such as a ruler or measuring cylinder. These can be reduced by observing from the correct angle. If a pointer is used, as in the case of an analogue meter, it should be kept close to the scale. 1 In some cases, the multiplier effect might not be linear; some readings may be increased by more than others. 8
80775_P001_075.indd 8
5/26/16 7:19 PM