1.

Measurement
A student is determining the acceleration of free fall g using a pendulum. State one precaution that you would
take in this experiment in order to obtain accurate readings.

Perpendicular viewing of rule

Counting beginning with zero
Use of set-square or horizontal rule to aid measurement of d
Use rule close to/touching the bob
Time taken from centre of swing, (not extremities)
Measure length to top and bottom of bob and average
Measure string length and add radius of bob measured with callipers or micrometer

The student pours the water from the cup into a measuring cylinder.
Draw a diagram to show water in a measuring cylinder. Show clearly the meniscus and the line of sight
the student should use to obtain an accurate value for the volume of the water.

line of sight perpendicular to measuring cylinder to the bottom of the meniscus

Line of sight
Ruler/meter rule - Measuring cylinder - Thermometer - Voltmeter / Ammeter - Balance / Stopwatch

2. Moment

To find the centre of gravity

places the metre rule, without the loads, on the pivot and adjusts its position so that the metre rule is as near
as possible to being balanced.
To place the mass/load accurately at the mark.
He places the metre rule on the pivot and then places block Q with its centre at the 95.0 cm mark.
The student stated that it is difficult to place the mass accurately at the 95.0 cm mark.
Explain how the student could overcome this. You may draw a diagram to help your explanation.

average of readings either side of the mark = 95 cm

measure width of mass (object),
add ½ width to the mark want to be place
so that it would get the mark of the edge of mass to be placed /
mean value of marks at both edges of mass /
mark centre line of mass and edge of rule
The student keeps block Q at the 95.0 cm mark and adjusts the position of the metre rule on the pivot
until the metre rule is as near to being balanced as possible.
Describe a method to find the point at which the metre rule is as near to being balanced as possible.

move the rule to find the point at which it just tips one way

In this experiment, it is difficult to determine the exact position of the load that will make the metre rule
balance.
(i) Explain briefly why this is difficult.
It is difficult to obtain the exact balance point.

(ii) Explain briefly how you would find the best position of the load that will make the metre rule balance.

If the metre rule doesn’t move or moves the least in its position and is almost stationary, it is considered as
nearest to being balanced and is the best position.

The student adjusts the position of the metre ruler on the pivot until the metre ruler is as near as possible to
being balanced.
Describe a technique for ensuring that the ruler is as near as possible to being balanced.
move the rule to find the point at which it just tips one way

3. Spring constant

A student investigates the behaviour of a spring, and then uses the spring to determine the density of
modelling clay.
Describe two precautions that the student should take when measuring the length of the spring, to
ensure an accurate reading. You may draw a diagram.
rule close / rule parallel to spring/ eye perpendicular to reading / use set square / clamp rule
The student plots a graph of load against extension for the spring, to show that the two quantities are
directly proportional.
State how his graph line shows that load and extension are directly proportional.
The graph line is straight line and
It is going through origin.

4. Cooling rate

Describe one precaution which should be taken to ensure that the temperature readings in the
experiment are as accurate as possible. /
A student is investigating the cooling of water. State two precautions that you would take in order to
obtain accurate readings in this experiment. /
Precaution reading the temperature readings in the experiment as accurate as possible.
view perpendicular to avoid parallax error
wait for thermometer to reach maximum temperature before reading
Stir before reading
line of sight perpendicular to scale
wait until reading stops rising (at start)
stir before reading
Place the thermometer without touching the beaker

Explain why the student should wait a few seconds after placing the thermometer in the hot water before
taking the first temperature reading.

To ensure thermometer / bulb / alcohol / mercury has reached the temperature of the water

A student plans to repeat the experiment using the same thermometer and the same volume of water.
Suggest two changes to the apparatus or the procedure that would increase the rate of cooling of the
water.

any two from:

higher starting temperature / use hotter water
use of metal can instead of beaker / metal bench
lower room temperature / cold water bath
use of a fan
container with a greater surface area / larger beaker

5. Electricity
Suggest one advantage of using a variable resistor to change the current in the circuit.

It can easily obtain large range of current values/ can easily set current to chosen values.

A student determines the electromotive force (e.m.f.) and resistance of a cell by using a resistance wire and plot
a graph of I / A (y-axis) against V / V (x-axis).

Suggest how the experiment and graph could be improved to obtain a more accurate value for e.m.f. E.

obtain more values at other potential differences

Suggest one reason why different students, carrying out the experiment carefully with the same
equipment, may not obtain identical results.
difficult to judge position of crocodile clip,
difficult to measure wire to nearest mm,
contact between wire and crocodile clip not precise,
difficult to interpolate readings on meters between marks
Suggest one practical reason why students carrying out this experiment may not obtain the same
readings as in Table 3.1. Assume that the procedure has been done carefully.
difficult to position crocodile clip accurately /
inconsistent connection with crocodile clip /
resistance wire not uniform

6. Light

Suggest one precaution that must be taken when setting up the apparatus to ensure accurate
measurements.
(lamp), object and lens at same height /
lens and screen perpendicular (to bench) /

A student is determining the focal length f of a lens.

Suggest two difficulties in this experiment when trying to obtain accurate readings.
Finding exact position that gives clearest image
Measuring to centre of lens
Room too bright/lamp too dim/image too faint

Describe a technique for obtaining an image that is as sharp as possible.

move screen slowly / back and forth

Describe one difficulty that is experienced when using a ruler to measure the height of the image in this
experiment. Suggest an improvement to the apparatus to overcome this.
Difficulty Ruler and the hand is going to get in the way due to the shadow.
improvement Use translucent screen and measure from the back of the paper.

A student is determining the focal length of a lens. State two precautions that you would take in this
experiment to obtain accurate readings.
use of darkened room / brighter lamp
mark position of centre of lens on holder
place metre rule on bench / clamp in position
ensure object and (centre of) lens are same height (from the bench)
object and lens and screen perpendicular to bench
move screen slowly / back and forth to obtain best image

In finding the formation of image

The student does this experiment with care.

Suggest a practical reason why the results may not be exactly those that the theory of reflection predicts.

difficulty in lining up pins / pins too thick / lines too thick / thickness of mirror (glass) / precision of protractor

A student investigates the refraction of light through a transparent block.

State one precaution that you would take in this type of experiment in order to produce an accurate
ray trace.
View the bases of the pins which is perpendicular/ vertical to the drawing board
distance between the two pins should be 5 cm at least.
A student carries out this experiment with care. Suggest a practical reason why the results may not be
accurate.
difficulty in lining up pins size of pin holes / thickness of pins / thickness of lines thickness of mirror

The student places two pins, P1 and P2, on line EN, as shown in Fig. 3.1.
Suggest whether the two pins are a suitable distance apart for accurate ray tracing. Explain your
answer.
statement ...................... not suitable ............................................................................................................
explanation .................... should be as far apart as possible ............................................................

A student investigates the refraction of light by a transparent block. He uses his results to determine a
quantity known as the refractive index of the material of the block.
Suggest a precaution which should be taken to ensure accurate results in this type of experiment.
look at base of pins/keep pins vertical use thin pins thin

Suggest why different students, all carrying out this experiment carefully, may not obtain identical
results.
difficult to align pins/place pins accurately / pins (too) thick / lines too thick

Possible inaccuracy
measuring cylinder scales less precise / accurate,
water lost on transfer / droplets on clay,
wood might absorb water