1969-06-01 — Page 13

育教儒頁一第張四第日七十月四年己麻袋 WAH KIUYAT PO

郭日僑筆

日期星 日一月六年九六九一公年八十五國民華中

育敎僑華

英中會考物理科答案

*

SECTION B

(鹽)

H.K.C.E.E. (English) 1969

PHYSICS

Suggested Answera

4.(a)(1) Coefficient of linear expansion of a body

The coefficient of linear expansion

a body is defined as the fractional change in length per degree changed in temperature,

(ii) Relation between the superficial expansion

and linear expansion

DNA

Besides expanding in length, a body expands in area when temperature increases, Suppose a square of original length of

is to be heated through one degree. The original length and be taken as unity,

11

is the original aras and is 1x11 unit

is the final length of each side

and is (1)

is the final area of the square and is (1+0)

But the final area A also equale to

(1 + B }\

fore,

4。 (1 + A) = (1 (1+6)=

20+x2)

Kis too small and can be

neglected:

A dziad S.G. bottle is first weighed empty, and then when full of the liquid at room temperature. This temperature is recorded and the bottle, together with the thermometer, is then placed in a hot water bath. The bath 18 then heated slowly to some higher temperature, stirring constantly to keep the temperature uniform. The bottle as then removed from the bath, dried on the outside, allowed to cool and finally weighed.

Measurement, and Calculation

Mass of S.G. bottle empty - ngu. Mase of bottle full of liquid at room temp

Mass of bottle and liquid after heating

Kass of liquid left in the bottle.

Mass of liquid expanded out

Room temperature.

degree

t degree o

Final temperature of hot water

Therefore, Coaffioient of apparent expansion of the liqui

"Mass of liquid escaped

mase of liquid remained temp. rise

.per dag.

(c)(1) it constant volume, the pressure of a given mass of gas is directly proportional to the absolute temperature. Therefore, the graph can be predicted as a straight line graph. Two points are sufficient to locate the straight line. These pointa arði-

at temp. of" 0°C and

co. of mercury

(B20)

at temp. of 100°C and preseure cn, of mercury.

88

761

88

The height-difference 18 12 cp.

(11) Large bulb and thin tubing to ensure

greater expansion for a small rise in temperature and the capillary tubing provides difficulty to the sucking in of ang merqury into the bulb,

5.(a) Latent heat of vaporisation of water

The latent heat of vaporisation of water is defined as the quantity of heat required to; change one gram of it from a liquid state (water) to a vapour state (steam) at the boiling-point.

(b) Determination of latent heat

The flask if filled with boiling distilled water to two-third full and is sure to cover the heater. A source of supply is chosen to deliver a constant current 3-5 amparas. When current is supplied to the circuit steam starts generating and drops of water come out from the condenser. When a steady state is reached, a weighed empty beaker, is place underneath the condenser to collect the water drops and at the same time start measuring the time taken by the atopwatch. When approximately 20 gm. of water 18 the beaker is removed and simultaneously stop the watch. The beaker and its content is reweighed.

While condensation is being collected, the readings of the ammeter and voltmeter are recorded..

Measurements..

Readings of the voltmetery volta Readings of the ammeter

Time takent sec.

Mase of the

I app.

Haus of the beaker and condensate

Conclusion

The coefficient of superficial expa.

or a body is twice the coefficient of linear)

expansion of the same body.

The original area of brass sheet

(102

#q#cu

The rise in temperature,

- 130 - 30 degrees C.

The coefficient or linear expansion of brass】

2 x 10 per

The coefficient of superficial expansion

of brass

* 10-5

final area of the brass sheet

(102

25) (1

75 x 1.004 75:3

x100)

Ans. The new area 18 75.3 sq.c

4. (b) Determination of the Apparent coefficient of

expansion of liquid Specific Gravity Nethod

Empty

230 neating

If the graph is produced it will cut the x-axis at point G which is known as the absolute zero, The triangles CAO and ABC are similar.

A

1 AD

БО

20)(100)

40

96 x 100

Mase of the condensate

Calculation

Heat energy taken to steam out the condensate)

MU calories

MLJ Joules

Electrical energy given out. Vit joules Therefore MLJ - VIT

VIt dal/gu

MJ

(c)(1) The graph of temperature against time

(ii) AB a constant heat of electrical energy

is applied to the thin beaker and its content (water) the temperature of the content rises until its boiling point is reached. Further supply of energy at this point will no further raise the temperature, but instead, the laquid now starts to change into atean. The graph at this stage. 194 horizontal lane indicating that the temperature remains constant.

(iii) Heating rate - o x (99 - 25) x cal/min)

200 x 74 x

cal./min.

7

Mass of water escaped - 200 – 196.

The absoļuve zero of temperature indicated to this experiment 18-240 deg. C..

If some water vapour exists inside tas bulb, a small rise in temperature will result in a much greater rate of increase. in pressure. If it is saturated, its rise is roughly exponential.

at a temperature of -20°C, from the graph the height-difference is (8 8-76) cm. By calculationi

+ 20

240

20

240

200

200 x 74 x

50 x 74 x

528.6 cal/g

Comments Heat used to heat up the glass beaker

1s not taken into account. The loss of heat to the surrounding cannot be neglected the beaker is not lagged. The result is not a satisfactory one.

H+

220

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