Q&A - PSLE Science

[janice_0950]

Dear all,

As shown in the following diagram, a thermostat is made of two different metals A and B, which are joined together. The two ends of the metals are fixed with a screw so that the ends will always be in line with each other. When the thermostat is heated, one metal expands more and it will cause the thermostat to bend.
(a) & (b) questions.....
Please help:(

A) You swopped the labels. B expands more, so obviously B must be the longer side.

B) Question and diagram is too ambiguous. What I think is that when you press the button down for too long and the iron gets too hot, the thermostat expands and the metal contact will be displaced and will cease to complete the circuit, hence stopping the heating coil from heating the iron anymore

Potted.Plant, thank you

[wi11anna]

Does raising a flag on a flag pole involve both a push and a pull? Thanks.

[Blue Pearl]

wow not easy.

[justMommy]

Your hand is exerting a pull force on the rope, and gravity is pulling the flag down.

[shann2]

I need help with this. It's under the topic of energy.





Thank you

[jojoberry]

I need help with this. It's under the topic of energy.



a. Heat energy comes from underground - geothermal energy
b. When cold water from the tank travels down the pipe, it gains heat from the ground and becomes warm. The warm water then returns to the hot water storage tank (it is less dense than cold water and rises).
c. it is a renewable source of energy
d. then the room temperature is the same temperature as the underground


Thank you

S - kinetic energy
P - Fossil fuels
Q - sun
R - wind

[NIEtrainedTEACHER]

Does raising a flag on a flag pole involve both a push and a pull? Thanks.

Raising a flag involves both a pull and a push. Your hand is pulling on the rope while the pulley at the top of the flagpole is pushing the rope through in order to raise the flag upwards.

[NIEtrainedTEACHER]

Hello,

Please help to answer this question:



Answer key given is (1), but i understand that red leaves are able to produce food by photosynthesis as well. Why is the answer not (3)?

Answer should be 3. Coloured portion of a leaf also contain chlorophyl and able to do photosynthesis.

The answer key is correct, the answer is 1. In variegated leaves, the portion which is green will be the area which photosynthesise. This can be further proven when a glucose/starch test is done using iodine. Doing such a test will show that the green portion will turn the iodine dark blue, while the non-green portion will not change the color of iodine.
As to the fact about coloured leaves having chlorophyll hidden, there are actually 3 different pigments.

Chlorophyll absorbs the red and blue light from the sunlight that contacts the leaf. Therefore, the light reflected from or transmitted through the leaf is deficient in red and blue light, so it appears green to our eyes. "Green" is the type of light used the least by chlorophyll. When a leaf has a high concentration of chlorophyll relative to other pigments, the leaf appears green.

Carotinoids absorb the blue-green and blue light from the sunlight that contacts the leaf. Light reflected by carotinoid pigments appears yellow or yellow-orange to our eyes. Generally, carotinoids assist chlorophylls in the process of photosynthesis. Carotinoid pigments are involved in forming the color of carrots. When a leaf has a high concentration of carotinoids relative to other pigments, the leaf usually appears yellow.

A third class of pigments found in leaves is the anthocyanins. Anthocyanins absorb blue, blue-green and green light. When leaves contain high concentrations of anthocyanins relative to other pigments, the leaves appear red or purple to our eyes. Anthocyanin pigments are involved in the red skin of apples, and the purple color of grapes.

A bit lengthy but I hope this helps.

[GBU]

Hui Ying hung two objects x and y on two identical springs. Which one of the following statements correctly explains why spring B is longer than spring A after the objects are hung on them?
(Object x is hung on spring A and object y is on spring B)

1) the mass of object y is more than that of object x.
2) spring A stretches less than spring B for the same amount of mass.
3) the elastic spring force acting on object y is less than that acting on object x.
4) the gravitational force acting on object x is less than that acting on object y.

Ans given is 1. Can the answer be 4? Tia

[GBU]

Hui Ying hung two objects x and y on two identical springs. Which one of the following statements correctly explains why spring B is longer than spring A after the objects are hung on them?
(Object x is hung on spring A and object y is on spring B)

1) the mass of object y is more than that of object x.
2) spring A stretches less than spring B for the same amount of mass.
3) the elastic spring force acting on object y is less than that acting on object x.
4) the gravitational force acting on object x is less than that acting on object y.

Ans given is 1. Can the answer be 4? Tia