Alternative A
Question 2A
An illuminated lamp is placed at equal distances between the two bulbs of the thermometers A and B as illustrated in the diagram above.
The bulb of thermometer A is covered with a shining silvery foil while that of thermometer B is covered with a dull black carbon paper.
Each thermometer reading is noted and recorded at equal time intervals of 60 seconds for 5 minutes
Fig. 2(a), shows the position temperature θAi of the thermometer A.
Fig. 2(b), shows the temperature θBi of the thermometer B.
Fig. 2(c), shows the corresponding time ti where i = 1, 2, 3, 4 and 5.
- Measure and record the real temperatures θA.
- Measure and record the real temperatures θB.
- Read and record the corresponding time intervals ti.
- Tabulate your readings.
- Plot a graph with θB on the vertical axis and t on the horizontal axis.
- Draw the best fit curve.
- Give a reason for the observed difference in the thermometer readings.
- State two precautions that are necessary to ensure accurate results when performing this experiment.
(b) (i) Explain why the outer surface of a tea pot is brightly polished.
(ii) State two methods of heat transfer.
Observation
Part (a) Performance was poor. Most candidates had difficulty in measuring the temperature readings, plotting of graph, determination of the slope and stating precautions in correct language.
Part (b) Candidates performance was above average.
The expected response:
- Five values of time t correctly recorded in seconds
- Five values of θARaw correctly measured to at least 1 d.p and
within tolerance of ± 0.1 cm
- Five values of θA correctly converted in oC
- Five values of θAReal correctly evaluated in oC (25oC + θAConv)
- Five values of θBRaw correctly measured to at least 1 d.p
and within tolerance of ± 0.1 cm
- Five values of θB correctly converted in oC
- Five values of θBReal correctly evaluated in oC (25oC + θBConv)
- Composite table showing at least t, θA and θB
- Plot a graph using reasonable scales
- draw line of best it
- deductions correctly stated
- state any two of the following precautions.
e.g.
- Ensured clamp/retort stand is firm
- Ensured thermometers are vertical/erect
- Avoided parallax error on thermometers/rule
- Noted zero error on rule
b(i) Reason Why the Outer Surface of a Tea Pot is brightly polished
Brightly polished surfaces radiate less heat than unpolished ones and will therefore retain heat inside the teapot for a longer period.
(ii) Method of Heat Transfer
e.g - Conduction
- Convection