Q19. Distinguish between concave mirror and convex mirror.
||Reflection takes place at the concave surface (bent in surface).
||Reflection takes place at the convex surface (bulging out surface).
||A parallel beam of light falling on this mirror converges at a point after reflection.
||A parallel beam of light falling on this mirror appears to diverge from a point after reflection.
||It is a converging mirror.
||It is a diverging mirror.
||It has a real focus which lies in the front of the mirror.
||It has a virtual Focus which lies behind the mirror.
Q11. What are strategic metals?
Ans. Strategic metals are those which are short in supply and are essential for the economy of a country or its defense.
Example: Titanium, manganese, chromium, zirconium.
Most of the metals have a high tensile strength; means load bearing capacity before they break.
Q10. Metals have great importance in our everyday life. Justify the statement.
What is the importance of metals in our everyday life?
Ans. Metals have great importance in our daily life because of the following reasons:
- Metals are used to make utensils( Aluminum, Copper).
- They are used in construction of building and bridges (Iron, Aluminum).
- In the manufacture of bodies of automobiles, ships, trains. (Iron, Aluminum etc).
- For making jewelry, furniture, electric appliances etc.
Q9. Explain the meaning of malleable and ductile.
Ans. Metals can be hammered into thin sheets. This property of metal is known as the malleability. The metals showing this property are called malleable.
Metals can be drawn into wire. The ability of metals to be drawn into thin wire is called ductility and the metals showing this property are ductile. Example: Gold, silver, copper.
One gram of gold can be drawn into a wire of about 2 kilometer length.
Q7. Define the following properties:
- Metallic Luster: Metals in their pure state having a shining surface is known as metallic luster.
- Malleability: Metals can be beaten into thin sheets without breaking.
- Ductility: The ability of metals to be drawn into thin wire.
- Sonorous: Ability to produce deep or ringing sound on striking with hard object.
- Brittle: Breaking easily when force is applied.
Q8. Why are electric wires coated with polyvinyl chloride or a rubber like material?
Ans. Polyvinyl chloride or rubbers are insulators. They do not allow electric current to pass through them so that even if we happened to touch the electric wires, the current should not pass through our body and hence we will not get electric shock.
Q6. What do you mean by allotropes.
Ans. Allotropes are the different physical forms of an element having same chemical properties but different physical properties.
Q5. What is exception among non metals?
Ans. Exceptions are:
- Non metals are generally solids( carbon, sulphur, phosphorus) or gases( oxygen, nitrogen, chlorine) except bromine which is a liquid.
- Iodine is lustrous non metal.
- Diamond is the hardest natural known substance.
- Graphite (allotrope of carbon) is a good conductor of electricity.
Q4. What are non metals?
Ans. They are non malleable, non ductile and bad conductor of heat and electricity. They possess low melting point and boiling point. They are brittle( break easily when force is applied). Example: Carbon, Sulphur, Phosphorus, Nitrogen, Oxygen, Iodine etc.
On the basis of chemical reaction non metals are defined as follows:
Non metals are those elements which form negative ions (anions) by gaining electrons. Show non metals are known as electro-negative elements.
Q3. What are exceptions in metals.
Ans. Exceptions among metals:
- All metals are solid but Mercury is a liquid at room temperature.
- Metals have high melting point and boiling points but gallium and cesium have very low melting points. These two metals melt if you keep them on your palm.
- Alkali metals (Lithium, Sodium, Potassium) are soft and can be easily cut with a knife. They have low density and low melting point.