errors, precautions, SOEs, improvements

Question 1

Explain zero error

Answer 1

it is the systematic error of a miscalibrated instrument which affects all measurements the same way. The measurements may either be too large or too small in on direction

Question 2

Explain parallax error

Answer 2

it is the poor experimental technique when the eye is in incorrect positioning when reading the scale on the instrument

Question 3

How to avoid parallax error in a measuring cyliner/thermometer?

Answer 3

read the scale by placing the eye on the same level as the top or the bottom of the meniscus

Question 4

How to avoid parallax error in a ammeter/voltmeter?

Answer 4

Align the image of the pointer seen in reflective mirror/mirror sheet with the pointer such that reflection is not seen which implies that the needle is viewed perpendicularly

Question 5

What are precautions?

Answer 5

To ensure the correct experimental techniques

Question 6

What are SOEs?

Answer 6

Things that affect the experimental result but nothing can be done about it without changing the apparatus or procedure.

Question 7

What are improvements?

Answer 7

To reduce/eliminate errors.

Question 8

Precautions for oscillations (general)

Answer 8

1. Ignore the first few oscillations and start the stopwatch after the oscillations have been stabilized.
2. Ensure that the pendulum is oscillating in a single plane by looking at the movement of the bob from the side
3. Record t taken for N no of oscillations so the measured time is more than 20s to reduce the percentage of uncertainty due to HRT which is 0.3-0.5s

Question 9

Precautions for oscillations (spring mass systems - T² and mass)?

Answer 9

Ensure the amplitude of the vertical oscillation is small so that the mass will oscillate in a single plane and minimize the effect of AR and hence improving the accuracy of the time taken and hence the calculated period.

Question 10

Precautions for oscillations (spring mass systems - T² and length)?

Answer 10

Ensure that the angle of the swing of the pendulum is small, less than 10°, so that mass will oscillate in a single plane and hence minimize the effect of AR and hence improving the accuracy of the time taken and hence the calculated period.

Question 11

Precautions for forces?

Answer 11

1. Ensure that the original length of the spring remains constant by taking readings of it in between each value obtained
2. Ensure the string attached to the Newton meter is vertical
3. Check that the meter rule is parallel to the table surface by using a half meter rule to check its vertical height from the surface at 3 diff points. (SOE: meter rule is not exactly horizontal)

Question 12

oscillations SOE:
difficult to ascertain start and stop of each osc without any ref line which affects t measures and hence T calculated

Answer 12

imp:
Use a fiducial marker to identify the equilibrium at the start of each reading. Allows for a easy identification of start and end of osc, hence easy counting of osc, improves accuracy of measured t and hence calculated T

Question 13

oscillations SOE:
friction at the point of suspension causes changes in the periodic motion hence reducing the accuracy of measured t and hence the calculated T, the variable to be plotted in the graph

Answer 13

imp:
1. apply oil on the pin
2. use smoother pin

Question 14

precaution:
1. small gap between cork and card, card and plumbline to reduce fric to ensure card can swing freely about the pivot pin
2. pin is perpendicular to the cork and the cork surface to reduce fric to ensure card can swing freely about the pivot pin

Answer 14

SOE:
gap causes difficulty in working the point on card where plumbline crosses bc which affects accuracy of measured y

Question 15

moments SOE:
1. difficult to determine the exact position of the center of mass as the mass does not have a uniform shape (irregular shape) which affects the accuracy of the measured L (distance of COG of mass from pivot)
2. the center of gravity of the mass M might not be at its physical center affecting the accuracy of L
3. plasticine may slip down

Answer 15

imp:
1. use uniformly shaped masses than have uniform densities so that the cog can be identified easily by determining the center of the mass and hence improves the accuracy of measured L

2. measure diameters separately and calc radius which can be added to measures length of spring to calc H
3. Mark the length of the spring from below the cork to the top of the bob to detect any slippage

Question 16

moments SOE:
1. difficult to ensure that the mass is hung exactly at the MP
2. difficult to measure AB without any reference point

Answer 16

imp:
1. mark MP using a pen
2. measure horizontal AC by placing meter rule across and divide it by 2 to obtain AB

Question 17

moments SOE:
difficult to ascertain when the rule is balanced horizontally which affects the perpendicular distance from the line of action of the force

Answer 17

imp:
1. use another ruler to measure and ensure the height of both ends of the suspended ruler is the same to ensure its horizontal
2. Try to visually align the ruler to a distant horizontal ref like the edge of teachers table or a window sill

Question 18

moments SOE:
difficult to read the marking on the meter rule as the string is too thick which affects the accuracy of the measured d

Answer 18

imp:
use a thinner string

Question 19

marble rolling down the slope SOE:
1. HRT when stopping and starting the stopwatch causes a large percentage error due to the short time taken for each reading, hence affecting the measured t.
2. the rulers used are not exactly identical and have the same texture, inconsistent texture between marble and rulers which affects the accuracy of t measured and hence v calculated

Answer 19

imp:
Increase the length of the slope so that the time taken for each reading will be larger which reduces the percentage uncertainty due to HRT

Question 20

Precautions for using syringe?

Answer 20

1. ensure no air/liq is in at the start by pushing the plunger all the way
2. ensure nozzle is fully submerged in the liq when liq is being taken up
3. raise plunger to pull up liq and take more than req vol

Question 21

Precautions for heating liquids?

Answer 21

1. liquid should be stirred constantly using a glass stirrer, not the thermometer, during exp to ensure that the temp is constant throughout the liquid before a reading is taken
2. therm/immersed object should not be in physical contact with the sides and the bottom of the beaker which may be in diff temp than the liquid
3. bulb of the therm must be fully immersed in the liquid so the measured temp of the liq is accurate
4. take reading only when liq column stops moving as it reflects temp of liq more closely and hence is a more accurate measurement

Question 22

thermal (heating exp with liquids and beaker) SOE:
(heat loss to surroundings) liquid will lose heat to the surrounding, reducing the accuracy of the measured temp

Answer 22

imp:
1. insulate the external surface of container with cloth (might touch naked flames)
2. cover the top of the beaker with a lid

Question 23

thermal (exothermic reaction) SOE:
instead of gaining heat from just the water might gain heat from the surroundings as well causing temp to be higher than the actual

Answer 23

imp:
use Styrofoam cup instead of a beaker to reduce the rate of conduction of heat from the surroundings

Question 24

SOE for waves

Answer 24

1. hrt when starting and stopping the stopwatch when wave starts and ends
2. height at which it is released
3. base of container is not flat (sides slope upwards which means measured L is smaller than L at the water surface), causes d to vary as wave transfers from side to side

Question 25

Precautions of light?

Answer 25

1. ambient light intensity (involving pins) 1. ensure pins are vertically upright using a protractor 2. optical pins, used to locate the path of light ray, are placed at least 6cm away from each other to reduce the possible range of wrong lines that can be drawn through the pin holes to reduce parallax error 3. ensure line drawn aligns with the back of the mirror as reflection occurs at the back of the mirror (using lens) 1. lens must the upright and parallel to screen and object using a set square to check (parallel to PA of lens) 2. illuminated object should be placed at the same vertical height as the optical center, using a ruler with a set square to ensure 3. obj distance and image distance should be measured along a line parallel to the principal axis

Question 26

light (involving pins) SOE: optical pin is too thick causing a large hole which increases the possible number of reflected/refracted rays and hence affects the accuracy of the measured angle of reflection/refraction (exact position of p3and4 which coincide with p1and2 are affected)

Answer 26

imp: use thinner pins/laser beams

Question 27

light (refraction-rectangular glass block) SOE: 1. pin position at P2 shifted the placement of glass block changing the angle of incidence and hence affecting the accuracy of the measured angle 2. difficulty in ensuring glass block is back at the exact loc which affects the measured angle of refraction

Answer 27

imp: 1. use pins with thinner shafts 2. pins with pin head that does not block the glass block 1. draw incident rays before putting glass block back, prevent replacing glass block and cause some shifting

Question 28

light (reflection) SOE: mirror is to lightweight and hence shifts when measurement is taken causing the inaccuracy in position of reflected ray

Answer 28

imp: use blu-tack to secure the position of the mirror

Question 29

light (lens) SOE: 1. range of values of distance, v, where the image of the obj appears to be focused on the screen 2. difficult to determine exact position where sharpest image occurs as our visual perception of the image differs

Answer 29

imp: repeat readings and find the average (can be one as a precaution as well) darker room for a more clearly defined image

Question 30

Precautions of electricity?

Answer 30

1. use a few correcting wires as additional may cause additional R 2. ensure electrical connection (croc clips are tightly clamped, plug key of switch is forcefully pushed down) are secure (do not fall off when shaken) so as to minimize contact R 3. jockey must be held vertically upright so readings obtained are precisely at a point 4. do not exert too much pressure on the R wire with jockey as it may change the CSA and create kinks 5. do not drag the jockey alone the R wire during the exp 6. switch off the circuit when not taking readings as heating effect may change the R of the wire 7. straighten the R wire as much as possible for better accuracy in measuring the length of the wire

Question 31

electricity SOE: kinks in wire so measured length is shorter than the actual length

Answer 31

imp: use a new piece of wire with no kinks precautions: straighten the wire by securing it with 2 screws fixed at each end of the ruler and tighten by turning the screws, wire will be straight and taut

Question 32

electricity SOE: there will be unavoidable heating of wires after prolonged use which will increase the R of the wire

Answer 32

imp: switch off the circuit when not taking readings to minimize the heating up of the wire due to the heating effect

Question 33

electricity SOE: CSA is not consistent throughout and hence R is diff at diff points of the wire

Answer 33

imp: do not drag the jockey along the R wire during the exp

Question 34

electricity SOE: inconsistent pressure on the R wire care can affect I and V readings

Answer 34

imp: do not apply excessive pressure, place jockey light on the wire