ATP- Paper 6

Question 1

Suggest why it is more accurate, when using a ruler, to measure D for five marbles rather than measure the diameter of a single marble.

Answer 1

effect of uncertainties reduced
diameters of marbles vary

Question 2

Describe how the student uses the two blocks and the marble to determine a new accurate value for the diameter of a marble.

Draw a diagram to show the arrangement.
Describe clearly how the student ensures that the value for the diameter of a marble is as accurate as possible.

Answer 2

use marble between two blocks and measure gap 1

suitable means of ensuring accuracy e.g.:
measure gap in at least two places and check equal to ensure blocks are parallel /
rotate marble to different axis and take average of measurements

Question 3

cylinder inaccuracy- source and improvement

Answer 3

graduations on measuring cylinder too large /
use smaller measuring cylinder or greater number of marbles /

Question 4

State two variables which must be controlled so that the comparison of x1 and x2 is valid. (temperature change over time)

Answer 4

same volume of water,
same material / thickness / surface area shape of beaker,
same room temp / named appropriate environmental condition

Question 5

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. (resistance calculation by length of wire)

Answer 5

difficult to position crocodile clip accurately /

inconsistent connection with crocodile clip /

resistance wire not uniform

Question 6

Describe the main difficulty that a student has when doing this experiment as accurately as possible. (balancing of a meter ruler on a pivot)

Using apparatus from Fig. 1.1, explain briefly how you would determine the position of the centre of mass of the ruler.

Answer 6

difficulty in obtaining exact balance
OR judging position of (centre of) load
OR masses sliding on ruler

balance ruler (on pivot with no loads).
pivot point is read / balance point shows centre of mass

Question 7

A student states that the average rate of cooling of the water decreases as the temperature comes nearer to room temperature.

(i) Suggest one change to the experiment that you could make to test the statement.

(ii) Suggest how to display the results to make it easier to see the trend in the rate of cooling.

(e) Explain briefly why it is good practice to read the thermometer scale at right angles

Answer 7

2(d)(i) continue taking temperatures / continue for a longer time (until close to room temperature)
OR use lower / higher starting temperature (of water)

2(d)(ii) plot a graph
of temperature against time OR cooling rate against time / temperature

2(e) to avoid parallax error

Question 8

State one precaution that you would take in order to produce an accurate ray trace.

Suggest one reason why different students, all doing this experiment carefully, may not obtain identical results.

In order to investigate further a possible relationship between values of (α + β), more values
are required. Suggest values of the angle of incidence α that the student could use. (pins are placed on this line)

Answer 8

 view bases of pins
 place pins (as) far apart (as possible) / > 5 cm apart
 ensure pins are vertical
 sharp pencil / thin lines / thin pins

difficult to align pins / place pins accurately / pins (too) thick. (getting pins vertical, lining up the pins exactly, drawing accurate thin lines), thickness of lines and mirror

at least 1 value < 30(°) and 1 value > 45(°) 1
all recorded values less than 90°

Question 9

A student states that the water cools slowly. Suggest two changes to the experiment that the student makes to increase the rate of cooling of the hot water without changing the starting temperature of the hot water. Room temperature remains constant.

Answer 9

 remove lid
 thinner lid
 paint the beaker black
 stir the water
 change beaker to container that is a better conductor / named metal- can
 increase surface (area of water / beaker)
 use a wider beaker
 blow air over water surface / use a fan
 use a smaller volume of water

Question 10

State one precaution that you would take to obtain accurate temperature readings. Explain briefly the reason for this precaution.

Answer 10

statement: view thermometer / scale / reading at right angles / eye level
explanation: to avoid parallax error

statement: stir (before taking reading)
explanation: to distribute water evenly / to ensure that all the water is at the same temperature

statement: ensure thermometer does not touch the side / base of beaker
explanation: temperature different to that of the bulk of the liquid

statement: wait until the thermometer (reading) stops rising at the start
explanation: so that the maximum temperature of the liquid is recorded

Question 11

The student uses a measuring cylinder to measure 200cm3 of water. He takes the reading from the bottom of the meniscus. Explain the reason for taking the reading at the bottom of the meniscus rather than at the top of the meniscus.

Answer 11

negligible / very small volume / amount of water between the bottom and the top of the meniscus

Question 12

A student suggests that angle β should be equal to the angle of incidence i = 20°.

State whether your result supports the suggestion and justify your answer. (yes)

Answer 12

YES
explanation of idea of beyond limits of experimental accuracy
e.g. values close (enough) / not too far apart / < 10% difference
if values are equal, it is sufficient to say just that the values are equal

Question 13

Describe a technique for ensuring that the ruler is as near as possible to being balanced

Answer 13

idea of allow to (just) tip one way then the other way

Question 14

Briefly explain one advantage of using a variable resistor to determine the resistance of resistor U rather than the procedure carried out in (b) and (c).

A student suggests that potential difference and current for resistor U are proportional. State how a graph of potential difference against current for resistor U can confirm this
suggestion.

Answer 14

can obtain continuous set of values /
more straightforward to change current /can obtain more values easily

straight line and through origin

Question 15

It is sometimes difficult to position the load W 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.

Suggest one possible source of inaccuracy other than the difficulty described in (d)(i). Assume that the experiment is carried out carefully.

Answer 15

suspend load from loop of thread / any other suitable method to avoid standing load over marks on rule

valid source of uncertainty e.g. test load not exactly 1.0
N / spring extension not linear / metre rule not uniform

Question 16

The student records the volume V to the nearest 1cm3.
Suggest why this is appropriate.

Answer 16

measuring cylinder can only be read to nearest 1 or 2 cm3.
to nearest cm3 means you are measuring the volume to 3 significant figures (which is sufficient)

Question 17

A student thinks the three resistors RA, RB and RC have the same resistance within the limits of experimental accuracy.

(i) Suggest how the student could use the apparatus provided to test his idea.

Answer 17

use of a voltmeter and/or an ammeter

measure V and I for each resistor and calculate R

OR connect each resistor to the same voltage supply and measure the current

OR connect resistors in series and measure the voltage across each of them

OR connect resistors in parallel and measure the current through them

Question 18

State two precautions that you would take to obtain accurate readings in this experiment. (A student determines the focal length f of a lens- triangle).

Answer 18

use darkened room / bright(er) object

move lens slowly (to find sharpest image)
move lens back and forth (to find sharpest image)

ensure that object, lens and screen are vertical

object and (centre of) lens same height (above bench)

perpendicular reading / viewing of the ruler scale

mark the centre of the lens on its holder

Question 19

(i) Suggest a suitable number of sets of readings that the student should take. and why

(ii) Explain briefly how this graphical method can give a more accurate value for the focal length.

Answer 19

any integer between 5 and 15 (inclusive)
greater accuracy / easier to line up pins

(a straight line) is a way of taking an average
anomalous results can be seen (and repeated or ignored)

Question 20

Another student does this experiment with the same starting temperature but in a room with a much higher room temperature than θR from (a)(i). State how this affects his value of x in d(i). Explain your answer by reference to the results in Table 2.1 for the beaker with 50cm3 of hot water.

(e) Some thermal energy is lost from the sides of the beaker.
The student wishes to find out how much this loss of thermal energy affects the cooling rate of 50cm3 of water. Briefly describe an additional experiment that the student can carry out to investigate this. Explain how the results can be used to determine how much this loss affects the cooling rate.

Answer 20

value of x will be less/lower
temperature difference between beaker and room is less and values from table referred to

repeat experiment with a lid
(calculate cooling rate) subtract from x to find cooling rate without transfer from sides OR a comparison of cooling rates

Question 21

Describe one difficulty when measuring the height of the image in this type of experiment. Suggest an improvement to overcome this difficulty. (triangle)

Answer 21

hand/ ruler gets in way of light

mark on screen and measure later OR
use screen with scale OR
use translucent screen and measure at rear

screen can move when measuring- clamp screen in place

Question 22

Suggest a suitable distance apart for pins P1 and P2 for this type of ray-trace experiment.

Answer 22

P1 P2 distance at least 5(.0) cm and no larger than 15(.0) cm

greater accuracy / easier to line up pins

Question 23

In order to investigate further a possible relationship between values of (α + β), more values are required.

Suggest values of the angle of incidence α that the student could use.

Answer 23

at least 1 value < 30(°) and 1 value > 45(°)
all recorded values less than 90°

Question 24

A student wishes to determine the resistance of the lamp RL when the potential difference across the lamp VL = 0.0V.
Describe how the experiment can be extended to do this with the help of a suitable graph.

Answer 24

obtain more values

and plot a graph of RL vs VL extend line to RL axis and read intercept

Question 25

Suggest why it was important for the student to add a small volume of water at the start of the experiment.

(g) Another student uses this experiment, with the same apparatus, to measure D for a small test-tube of diameter approximately 1.2cm. He adds water in volumes of 1.0cm3 at a time.
State and explain one reason why this is not an accurate method to use for this test-tube.

Answer 25

inside diameter near base not uniform

1(g) valid critical comment e.g.:
water volumes small – large uncertainty in measuring cylinder
test-tube diameter small – large uncertainty in answer /
height changes small so unreliable

Question 26

Explain briefly how to use the string and the metre rule to determine the circumference c as accurately as possible. You may draw a diagram.

Answer 26

wind string round beaker (several times)
measure the length of the string (and divide by the number of turns)

Question 27

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.

Answer 27

rule close
rule parallel to spring
eye perpendicular to reading
use set square
clamp rule

Question 28

(e) Suggest a possible source of inaccuracy in the determination of ρ in this experiment. (Load U is fully immersed in a beaker of water- length of spring measured)

Answer 28

part of load U is metal
hanger immersed too
clay wet when weight measured
air holes in clay
air bubbles on immersed clay

Question 29

Another student wants to obtain a more accurate value for V1. He uses the method of floating the block of wood in water as described in (b). Suggest how the student could obtain a more accurate value by taking a measurement.

Answer 29

(float wood and) mark water level / remove and mark the water level
measure submerged depth and multiply by the cross-sectional area

measure height of block that is not submerged
multiply by the cross-sectional area then subtract from total volume of block.

use of a measuring cylinder / displacement can
measure the volume of water displaced (by the floating block)

Question 30

Suggest one practical difficulty with this experiment. Explain briefly how you would try to overcome this difficulty in order to obtain accurate results. (investigating image produced by lens).

Answer 30

deciding the screen position for most clearly focused image
move screen slowly / backwards and forwards

OR
the image is difficult to see
carry out in a darkened room / away from bright lights

OR
(metre) rule moving
clamp rule / tape rule to bench

OR
the image is (small and) difficult to focus
use a bigger object

OR
difficult to find the centre of the lens
use a marked lens holder

OR
object, (centre of) lens (and screen) are not at the same height above the bench
use a ruler / set-square to check

difficulties- (Finding exact position that gives clearest image. Measuring to centre of lens. Room too bright/lamp too dim/image too faint)

Question 31

Describe one difficulty that can be experienced when measuring the height of the image.

Answer 31

ruler in way of light /
difficult to see top and bottom of image / edges of image blurred /
difficult not to move screen when placing ruler to measure image

matching solution e.g.:
use graph paper on screen / mark top and bottom of image and measure later / use translucent screen and measure at back / use larger object / clamp screen (after obtaining focus)

Question 32

State one variable, other than the initial temperature, which the student should control

Answer 32

SUGGESTION: smaller cooling rates (at equivalent times)
EXPLANATION: reference to cooling rate being smaller at lower temperatures and values stated

OR
SUGGESTION: smaller difference(s) in cooling rates (between equivalent times)
EXPLANATION: clear reference to (x2 –x3) being smaller than (x1 –x2)

Question 33

The ammeter in this circuit has a small resistance which affects the current. The effect of this resistance on the measured current I will be different for each measured length l of the
resistance wire.

State and explain which length l will be most affected by the resistance of the ammeter

Answer 33

smallest length.
ammeter forming greater proportion of total resistance. (resistance of wire decreases so more resistance in ammeter)

Question 34

Suggest a possible source of inaccuracy in this experiment, even if it is carried out carefully. (reflection of light by a plane mirror)

(f) A student wishes to check if his values for a are reliable.
Suggest how he could improve the experiment, using the same apparatus, to check the reliability of his results.

Answer 34

ray has finite thickness – (difficult to mark position of ray precisely),
reflecting surface of mirror at rear,
inaccuracies have more effect for smaller angles,
small variations in mirror angle have significant effect on ‘a’

1(f) reflect ray below NL at same angles
and take averages

Question 35

One student places the meter rule on the pivot at the 50.0cm mark and then places block U with its centre at the 5.0cm mark. Suggest why it might be difficult to place block U accurately at the 5.0cm mark. Explain how the student could overcome this difficulty. You may draw a diagram.

Answer 35

(difficult to see centre of block) and valid method, e.g.
* (measure width of block and) add ½ width to 5.0 cm to find position for edge of block
* mean value of marks at both edges of mass
* mark centre line of mass and align with mark on rule

Question 36

It is difficult to read both thermometers every 30s. Describe briefly a technique that would ensure the temperature readings are as accurate as possible in the experiment.

Answer 36

• place stop-clock and thermometers so seen easily
• keep eyes at level to thermometer scales
• use an audible 30 s alarm
• read temperatures alternately every 15 s
• use of data logger

Question 37

Suggest two changes that could be made to the apparatus or the procedure to ensure that the temperature θC of the cold water in the boiling tube rises more quickly

Answer 37

• thinner walls on tube
• metal tube
• bung/lid on tube
• insulate sides of beaker/lid on beaker
• higher initial hot water temperature
• lower initial cold water temperature
• increase volume of hot water
• decrease volume of cold water
• stirring

Question 38

Suggest two ways in which the student could reduce the rate of loss of thermal energy from the beaker in this type of experiment.

Answer 38

Insulate
Lid
Lower starting temperature
Higher room temperature
Smaller volume of water
Smaller surface area

Question 39

A student notices that the resistance wire becomes very hot when the crocodile clip is connected to short lengths of the wire. Suggest an improvement that would help to reduce this effect.

Answer 39

use smaller current / potential difference;

use wire with greater resistance;

open switch / switch off circuit in between readings.