Sources of Error and precaution Compilation

Experiment Sources of Error Precaution Balancing ruler / moments 1. The retort stands are old and rusty, it is difficult to make small changes to height of the metre rule. Thus the metre rule may not be exactly horizontal. 2. The reference point where it is u sed to measure the length of spring may not be consistent. Hence, affecting length l. 3. To measure l, the 30 cm rule has to be held vertically by hand. However, error is incurred in this measurement as the rule could not be held steadily. 4. The spring does not stretch linearly (or has too small an extension) for smaller values of x near the pivot. 5. The mass may have shifted and the distance between the weight and pivot will be different. T herefore affecting the force that is needed. 1. Ensure the ruler is horizo ntal by measuring the distance from the ruler to the table at both ends. These distances should be the same. 2. Read the ruler (to obtain length of spring) at eye level to avoid parallax error, so as to have accurate reading of length l. Period of oscillation 1. The thread may be slightly elastic, therefore affecting length of pendulum. 2. The t hread may have slip through the split cork, therefore affecting the length l of pendulum. Improvement: Take the length before every reading. Precaution: Allow the pendu lum to swing a few times before starting to record the time. Centre of gravity 1. The plumbline and the card will move/oscillate if the ruler touches it. This makes it difficult to measure x accurately as ruler cannot be placed against the card. 2. The mass of each paper clip may not be the same, thus the relationship between x and n may not be correct. Refraction through two glass blocks 1. Due to the size of the paper, the pins could not be placed far apart. This may cause inaccuracy in the loca tion and measurement of ray P1P2. 2. The holes made by the pins provided are rather large thus affecting the accurate construction of the paths of incident and emergent rays. 3. The bevel edge of the glass block do not allow the tracing of the glass block to be accurate. Therefore, the glass block may not be placed back to the original place, thus affecting incident angle. Total internal reflection 1. The holes made by the pins provided are rather large thus affecting the accurate construction of the paths of incident and emergent rays. 2. The bevel edge of the glass block do not allow the tracing of the glass block to be

accurate. Therefore, the glass block may not be placed back to the original place, thus affecting incident angle. Reflection 1. The mirror is very light and shifts during the experiment. This causes error in the angle of incidence and hence the emergent ray. 2. The holes made by the pins provided are rather large thus affecting the accurate construction of the paths of incident a nd emergent rays. Focal length of a convex lens 1. The ed