Polishing

Q.

What are the three stages of Heat treatment?

Q.

The resistivity of an alloy is higher than its constituent metals. Give reasons.

Q. Metals have lustre (shine). Give reason why some metal articles become dull and lose their shine after sometime.

Q.

19. Give the reason why some metals become dull and lose their shine.

Q. White and polished surface reflects more heat than

1. black surface.
2. rough surface.
3. black and polished surface.
4. black and rough surface.

Q.

All metals exist in solid form at room temperature.

1. True
2. False

Q.

Shining surfaces are ________ absorbers of heat energy.

Q.

Which type of solid is Chromium?

Q. Which of the following object loses its shine when exposed to air and water?

1. Rubber
2. Plastic
3. Wood
4. Iron

Q.

The type of paints are used for the exteriors of the building?

Q.

A tarnished silver rod when kept in water containing magnesium bars regains its lustre. Justify.

Q.

How do you keep aluminum shiny?

Q.

Give reasons for the following

a. A silver object gradually turns black when left in open.

b.Gold ornaments retain their lustre even after several years.

Q. Polishing of the metal surface increases the durability of the metal. State true or false.

1. True
2. False

Q. A substance X was given to a student, he was asked to identify it using its properties. It was a lustrous non-metal. It was able to conduct heat. Identify X

1. Bromine
2. Diamond
3. Sulphur
4. Graphite

Q.

Statement given below is incorrect. Write the correct statement.

The metallic wires contract during summer and can break.

Q. What is lustre? Give two examples of materials that possess lustre.

Q.

Natural rubber is heated with an element X to make it hard, strong, and more elastic. X is

1. Zinc

2. Sulphur

3. Lead

4. ${\mathrm{H}}_2$

Q. Which of the following object loses its shine when exposed to air and water?

1. Rubber
2. Plastic
3. Wood
4. Iron

Q. Choose the lustrous substance from the given options.

1. Paper boat
2. Wooden table
3. Plastic chair
4. Copper bell

Q. Which property of material gives shiny appearance to objects?

1. Solubility
2. Hardness
3. Transparency
4. Lustre

Q. Which of the following object loses its shine when exposed to air and water?

1. Rubber
2. Plastic
3. Wood
4. Iron

Q. Choose the lustrous substance from the given options.

1. Copper bell
2. Wooden table
3. Paper boat
4. Plastic chair

Q. Which property of material gives shiny appearance to objects?

1. Hardness
2. Transparency
3. Lustre
4. Solubility

Q.

Which of the following collections are sets?

Your favorite clothes

Q. (b) Give one use of each of the following: brass​

Q.

In my book its written black objects rradiate and absorb more heat than white objects. Thus the back of refrigerators is coloured dull black so that they can raiate maximum hat to cool down the refrigerator pipes.

BUT BLACK COLOUR OBJECTS ABSORB MORE HEAT TOO. THEN REFRIGERATORS WILL HEAT UP. ISNT IT?

Q. Find the odd one out of the following substances​ based on their uses.​