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Mechanics M.M.Fazeel B.Sc M.Sc PGDE01. In an experiment to find the density of coconut oil you are provided with the following:

(1) U-tube on to a vertical frame with appropriate scales

(2) Water and sufficient amount of coconut oil

(3) Funnels

(a) (i) Draw a labeled diagram of the experimental setup, clearly showing the levels of water and coconut oil

columns and their common interface.

(ii) On the diagram draw above mark, as and , the two measurements that you have to take.

(b) If the densities of coconut oil and water are given by respectively, write down an expression for in terms of

.

(c) (i) Select the correct procedure out of the following in order to draw a graph in determining

(1) Adding more water to the respective arm.

(2) Adding more coconut oil to the respective arm.

.

(ii) Give the correct reason for not selecting the other procedure.

.

(iii) In such a graph the gradient is fount to be 0.87. Determine the density of coconut oil

(density of water = 103

kg m-3

).

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Mechanics M.M.Fazeel B.Sc M.Sc PGDE(d) In this experiment which liquid should be poured into the U-tube first. Give reason for your answer.

.

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(e) If you want to determine the density of coconut oil with a fractional error of 0.1, water should be the minimum

height possessed by a liquid column? Assume that the height of a liquid column can be measured with an

accuracy of 1 mm.

.

.

(f) What is the experimental disadvantage of using mercury instead of water in this experiment?

..

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02. Figure (1) shows an experimental setup of Hares apparatus

used in a school laboratory to measure the relative density

of a liquid. If the figure, water and liquid are labeled as A andB

respectively.

(a) i. Give an approximate value for the diameter in cm, of thetube in both arms in a Hares apparatus normally used in a

school laboratory

ii. Name the measuring instrument that is not shown in the

figure given but needed for the experiment.

.

iii. State clearly how you would establish and maintain waterand liquid columns in the arms of the Hares apparatus.

iv. What is the special advantage of this method over the U tube method ?

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Mechanics M.M.Fazeel B.Sc M.Sc PGDE.

(b) In order to determine the surface tension as well as the

density of a liquid a student has modified the Hare s

apparatus by replacing its both arms with identical tubes

of internal radius r, as shown in figure (2).

i. Let P0 be the pressure of air above the water and liquid

meniscus, (h W, hl ) be the heights of the columns, (dW, dl)

be the densities and (Tw , Tl) be the surface tension of

water and liquid respectively.

If Pw, PL are the pressures at point W and L respectively,

write down expression for PW and PL in terms of relevant

parameters.

Assume that the contact angles of water and liquid with glass are

zero.

.

.

ii. Hence derive an expression for hwin terms ofhl, dw, dl, Tw, Tl, r and g in the form ofy = mx + c.

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iii. If you graph of hw versus hl, and if you know the value of dw, Tw, r and g what quantities you should

extract from the graph to determine Tl and dl .

.

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iv. Why is it always suitable to have the heights of the water and liquid columns as large as possible ?

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Mechanics M.M.Fazeel B.Sc M.Sc PGDE

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