difficulties-and-improvements-物理实验中存在问题与解决方案讨论.doc

Source of error: two sets of readings are not enough to draw valid conclusion.
Improvement: Take more readings and plot a graph

Measuring height of water/depth of water:
Source of error: Difficulty to measure height owing to refraction effects (shape of bottle).
Improvement: Add dye
Use paper behind the bottle
Use mirror behind bottle

Set up the apparatus:
Source of error: Difficulty in setting up the line/ruler/strip horizontally or vertically:
Improvement: Use set square on the bench to ensure that …….. is horizontal or vertical.
Measure each end of rule to see if distance about bench is the same.

Measuring height (including height of water) or length in vertical direction:
Source of error: Parallax error in measuring h
Improvement: Use set square from ruler to ……..to indicate height
get eye level perpendicular to the ruler scale
place the ruler as close as possible to the ……
put scale onto bottle

Measuring distance in horizontal separation:
Source of error: Parallax error in measuring d
Improvement: Place ruler under path and use shadow projection
Use set square as markers, place ruler under path and view vertically from above

Measuring length
Source of error: Parallax error in reading the length
Improvement: place scale on the blade

Deciding an instant:
Source of error: difficulty to measure h as the ball is moving quickly.
Improvement: Use video camera and play back with slow motion to measure h accurately.
Source of error: difficulty in judging the end point
Improvement: mark the distance with lines on ramp

Size of increment:
Source of error: difficulty in judging when the bottle was about to topple
Improvement: trial and error, bring bottle closer to point of toppling.
Hold with newton meter and tilt until F=0
Source of error: Poor accuracy due to size of increment
Improvement: use smaller increment
Source of error: Use of increments imprecise
Improvement: Use smaller mass increments

Measuring angle:
Source of error: difficulty in measuring angle owing to container not perfectly right angled at the bottom.
Improvement: make bottle square with plasticine.
Source of error: parallax error in measuring angle on the protractor
Improvement: get eye level perpendicular to the protractor lines.
Source of error: thick strings make measurement of angle hard.
Improvement: use thinner strings/rules
Source of error: difficulty to accurately locate the center of knot.
Improvement: use thinner strings

Measuring diameter/radius:
Source of error: …….is not circular ( …… was flexible ), leading to an inaccurate value for diameter/radius
Improvement: use vernier caliper to measure diameter in different directions and average.

Measuring time:
Source of error: human error in timing………..
Improvement: Video the oscillations and play back frame by frame
use light gates to trigger a timer

Measuring period:
Source of error: Oscillations are too quick to time manually.
Improvement: Video the oscillations and play back frame by frame
Measure the time for a greater number of oscillations and average.
Source of error: Difficulty in judging complete oscillation.
Improvement: Use a fiducial marker to ensure the complete oscillation.

Ensuring Center of mass
Source of error: difficulty in establishing center of mass of the ball
(difficulty to measure l because it is hard to judge the position of center of the ball)
Improvement: Find the mid-point of the mass by finding the distance to both ends and taking an average ( measure l to both ends of the ball and average)
Mark the center of the ball

Releasing the object:
Source of error: difficulty to release the ball without applying a force
Improvement: Use a remotely operated clamp to release the ball.
Use an iron ball and electromagnet to release it.

Measuring length in circle:
Source of error: The length of wire in one turn is different from the tube circumference because thread is spiral.
Improvement: mark the wire and measure the straight length.
measure the length in one turn by wrapping string, then unwrapping and measuring/workable method of getting even spacing of turns.
Wrap so coils are closer

Unwanted resistance
Source of error: contact resistance
Improvement: clean the contacts
Source of error: lead resistance
Improvement: use shorter leads
reposition voltmeter connections closer to contact

Judging the position for moveable contacts
Source of error: difficult to judge whole number of turns when positioning contacts
difficult to measuring 45cm length because wire not straight
Improvement: use smaller plug /use smaller crocodile clips
mark lateral line on tube to give positions for contacts
measure 45 cm with the wire straight, mark lateral line on wire to give positions for contacts

Fluctuation:
Source of error: fluctuating current/ fluctuating voltmeter readings
Improvement: use smaller crocodile clips to connect the circuit

Inconsistence:
Source of error: inconsistent bounce/inconsistent collisions
Improvement: use flat surface/use smoother brick
Source of error: change in properties of thread due to repeated drops
Improvement: use a new thread each time

Air movement:
Source of error: Motion of ball affected by air movement
Improvement: turn off fans
Turn off air condition

Operation:
Source of error: Difficulty to hold both cylinders and tracing paper
Improvement: Use clamps to hold cylinders
Use another person to hold tracing paper
Source of error: Difficulty to hold ruler/protractor/plug still
Improvement: clamp the ruler/protractor/plug
Source of error: difficult to add mass without swinging the hanger
Improvement: support underneath and remove hand slowly