Practical Flashcards
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oscillations
Suggest how the procedure can be improved to increase the accuracy of the result.
time a greater number of oscillations, so timing errors have less effect
The ammeter is not broken.
Suggest what the student may have done incorrectly while setting up the circuit.
diode causes current to flow in the wrong direction
ray trace
The measurement of a quantity is reproducible if a similar result is obtained when the measurement is repeated by a different method or under different conditions.
Suggest how the student can adapt this experiment to check if the value of d/1 is reproducible.
repeat with optical pins OR
repeat with = 60 on the other side of the normal
How to obtain more reliable readings.
repeat each reading and calculate an average value
How to accurately measure the volume of liquid in a measuring cylinder
Read below meniscus.
Line of sight perpendicular to the scale.
How to measure diameter of a rod
Use of rod between two blocks and measure gap in at least 2 places, ensuring blocks are paralell and take average. Use a micrometre.
Explain briefly why the position of the pivot may not be exactly at the 50.0 cm mark of the rule.
center of mass of ruler not at the center
Precautions while measuring volume of wooden rod →
Wood might absorb
water, measuring cylinder scale not precise
Why it is useful to take a trial reading for a experiment?
to check if dependant is measurable, to check if independant value is appropriate. (Can be measured accurately) Set a good range of d and t values.
How to ensure if scale is horizontal?
Measure the distance between the metre rule and bench in two different places, If the distances are equal, the metre rule is horizontal.
It is difficult to position the load on the scale of the metre rule at the correct distance d from the pivot.
Suggest one change to the apparatus to
overcome this difficulty.
Measure length of one side, halve, mark point.
suspend load from loop of thread
align with mark on rule
How to make sure the length, l of the pendulum bob is as accurate as possible →
Measure the top and bottom of bob and average
View perpendicular to the scale
Rule parallel with string. Use of set-square
Keep the rule close to the pendulum
How to get temperature reading from a thermometer as accurate as possible?
Line of sight perpendicular to scale.
Stir mixture before.
Wait for it to stop rising at the start, so the max is recorded.
Comparison - keep the thermometer at same depth
don’t let thermometer touch the bottom/sides of the container
loads and springs
What is the source of inaccuracy
in this experiment →
test load not exactly 1.0 N /
spring extension not linear /
metre rule not uniform
What are the control variable while measure the rate of cooling/heating of water in a beaker →
Same volume of water
Same initial + room temperature
Same SA, material, and height of container
Same duration of experiment
How to reduce loss of thermal energy from beaker →
insulation
lid
lower starting temperature
higher room temperature
smaller volume of water
smaller surface area
Experient for how lid affects the rate of cooling.
Repeat same experiment
without a lid. calculate cooling rate and subtract cooling rate with lid.
Possibile errors in ray trace experiments →
lines not thin, draw thin lines using sharp pencil
Difficulty to align pins, view bases of pins
Pins too thick, use thin pin
Inaccuracies have more effect on small angl
ensure pins are far apart and upright
Why 2.7cm pin separation is not suitable →
pin separation should be as large as
possible for greater accuracy
What are the possible difficulties in resistance wire experiments →
Difficulties to judge position of crocodile clips
Difficult to measure wire to nearest mm
Difficult to figure out readings on meters between marks
contact between not precise
How must a variable resistor be placed with reference to resistance wire?
in series
Precautions in lens experiments →
Darkened room
Moving screen slowly to obtain best image
Mark block to show centre of lens
Clamp rule to bench
Lens and object and screen upright
Lamp, lens, object at same height
Describe how the experiment can be extended with the help of a suitable graph.
Obtain more values. Plot a graph (axis specified). Extend the line to R axis and read intercept.
The student adjusts the position of the metre rule until it is near as possible to being balanced. Describe a technique.
Find the point where it tips to one side and the point where it tips to the other. Between these points is the balance point.
How to obtain the sharpest image?
Move the screen back and forth slowly.
Difficulty experienced when using ruler to measure height of image.
Ruler and hand gets in the way of light and makes shadows. Use a translucent screen and measure from the back of the translucent screen/paper.
light trace
Suggest a distance.
5
5-15
light traces
Investigate the relationship further.
many values above and below
Suggest how to test that the centre of mass is at 50cm indeed.
Without mass. Read position at which it is near as being balanced as possible.
Advantage of variable resistor compared to calculating R.
Easier to change current to certain chosen values.
Easy to obtain more values and to set a large range of values.
Testing if values are directly proportional.
Plot graph. *specified
calculate T/D
temperature
Suggest how to continue the experiment to support the suggestion.
more readings until room temperature
Why is it more accurate to measure 5 marbles?
The effect of uncertainties is reduced.
Improvement to displacement method.
graduations on measuring cylinder is too large ->
use a smaller measuring cylinder, greater number of marbles
Write a conclusion on the cooling.
greater overall temp change at A than B, because starting temperature is greater, (reference to values)
compare times taken to reach a fixed temp drop
combined resistance Vs combined resistors
Explain how to extend the investigation to further investigate the relationship.
Use another resistor. Add at least three more resistors (one at a time)
Possible sources of inaccuracy in apparatus + sand.
sand surface not flat
balance only to nearest gram
metre rule not uniform
volume of sand particles
Explain why method one is not suitable.
Air gaps between sand add to the volume, so it appears bigger than it is.
How to reduce the effcet on cooling rate?
water bath
Changes to increase cooling rate.
remove lid
use smaller volume
thinner lid, stir water, beaker that is a better conductor (paint black)
Explain the reason for taking the reading at the bottom of the meniscus.
Amount of water between the top and bottom of the meniscus is negligible.
ball and metre rule
Distance from ball to start of metre rule?
end-end=2
2/2=1
end 1 + 1= result
starting end to centre of ball
x-axis is light intensity, y-axis is resistance of LDR
What is the control variable?
type of light source, angle of light source relative to LDR, p.d
Measure distance deflected by wooden strip?
ruler
deflection of wooden strip by load
What are the controls?
type of wood, length and width of wooden strip, humidity
force to break different metal wires
How many metals to mention?
Describe repeat.
3, repeat for new values of independant variable (the other two metal wires)
Suggest why the value of VA is only an approximation of the volume of the block.
difficult to measure irregular dimensions, repeat in several places for each dimension and take averages
Method 1: volume using formula, balance for mass
Method 2: volume using displacement, force
Which will give a more accurate density?
2) volume is measured directly
A student decides to continue the experiment using larger values of u.
Explain why this produces less accurate values for W.
b, which is used to calculate is too small, difficult to measure
metre rule, pivoy, load
Suggest one practical reason why it is difficult to obtain exact results with this experiment.
difficult to achieve balance
The student notices that the lamp does not glow when he takes the final set of readings. He
thinks that the filament has broken.
State whether the student is correct and give a reason for your answer
No, there is a current reading
A student suggests that the resistance R of the lamp filament should be constant.
Suggest, referring to the observations, a reason why the resistance R may not be constant in
this experiment.
filament changes brightness, change in temperature
Suggest one practical reason why measuring the time for 200 oscillations, rather than
20 oscillations, may not be suitable.
student may lose count
Suggest a practical reason why the result obtained from the experiment may be different.
(pendulum)
student did not react fast enough when starting and stopping stopwatch, difficulty measuring accurately from the centre of the bob
Suggest two improvements to the experiment. (pendulum)
use of different lengths, repeat timing, increased number of oscillations
Why angle i is NOT equal to angle r in ray experiment:
Thickness of pins
Thickness of mirror
Protractor is not precise
Inaccuracy of ray box method
thickness of rays.
Centre of mass experiment (with the lamina):
You view the string directly in front of the card.
Minimizing the heating effect of a current
Decrease voltage
Decrease the resistance of a resistor
How to check if a rule is vertical
use a set square
Variables in experiments about springs and stretching effect:
Number of coils
Length of spring
Diameter\thickness of spring or wire
Selection of loads
Improvement made to calculating circumference by string method
Avoid parallax error
Thinner string
Parallel winding of springs
Precautions for circuit readings of I and V so that they are accurate
For I specifically:
Limit current so that temp. doesn’t increase
Use a tapping meter
For I and V: Switch off between readings.
Fair test for pendulum experiments
Length of pendulum
Shape of bob
No. of swings
Amplitude
Precautions and procedures in electrical experiments
check for a zero error
Always check polarities before closing the switch (completing the circuit)
