Wednesday, June 6, 2012

CBSE - Class 6 - Science - CH 13 - Fun with Magnets

NCERT Chapter Solutions

Magnetic Hill at Leh road (India) - which can pull cars
(source: wikipedia)

Q1: Fill in the blanks in the following:

Answer:
(i) Artificial magnets are made in different shapes such as _bar-magnet_, _cylindrical_ and _horse-shoe magnet_.

(ii) The Materials which are attracted towards a magnet are called_magnetic materials_.

(iii) Paper is not a _magnetic_ material.
(Explanation: Paper does not attract to magnet. Therefore it is a non-magnetic material).

(iv) In olden days, sailors used to find direction by suspending a piece of _bar magnet_.

(v) A magnet always has _two__ poles (i.e. North Pole and South Pole).




Q2: State whether the following statements are true or false.

Answer:

(i) A cylindrical magnet has only one pole. - False ()

(ii) Artificial magnets were discovered in Greece. - False - ()

(iii) Similar poles of a magnet repel each other. - True - ()

(iv) Maximum iron filings stick in the middle of a bar magnet when it is brought
       near them.- False - ()

(v) Bar magnets always point towards North-South direction. - True - ()

(vi) A compass can be used to find East-West direction at any place. - True - ()

(vii) Rubber is a magnetic material. False - ()

Q3: It was observed that a pencil sharpener gets attracted by both the poles of a magnet although its body is made of plastic. Name a material that might have been used to make some part of it.

Answer: The blade of the pencil sharpener is made of iron. Iron is a magnetic in nature. That's why the sharpener gets attracted by the poles of a magnet.

Q4: Column I shows different positions in which one pole of a magnet is placed near that of the other. Column II indicates the resulting action between them for each situation. Fill in the blanks.

Answer
    Column I                  Column II      
   N-N   Repulsion
   N-_S_   Attraction
   S-N   Attraction
   _N_-S   Repulsion


Q5: Write any two properties of a magnet.
Answer:
  1. Each magnet has two poles i.e. North Pole(N) and South Pole(P)
  2. Opposite poles of two magnet attract each other while like poles of two magnet repel each other.
  3. A freely suspended magnet always aligns in N-S direction.
Bar Magnet
(src:clker.com)

Q6: Where are poles of a bar magnet located?

Answer: The two ends of the bar magnet represents the two poles.


Magnetic Compass
(src:clker.com)
Q7: A bar magnet has no markings to indicate its poles. How would you find out near which end is its north pole located?

Answer: Hang up the magnet by a cotton thread so that it hangs freely. When it comes to rest, we notice that the magnet is lying in a North - South direction.

Magnetic compass works on the same principle. In past it was used by sailors or travellers to find directions.





Q8: You are given an iron strip. How will you make it into a magnet?

Answer:
  1. Take a rectangular piece of iron. Place
    it on the table.
  2. Take a bar magnet and place one of its poles near one edge of the bar of iron.
  3. Without lifting the bar magnet, move it along the length of the iron bar till you reach the other end.
  4. Lift the magnet and bring the pole (the same pole you started with) to the same point of the iron bar from which you began 
  5. Move the magnet again along the iron bar in the same direction as you did before. Repeat this
    process about 30-40 times.
  6. Bring few allpins near to the iron bar and check if it is converted to a magnet or not.
 Click here to see the method is explained with pictures.


Compass Directions
(src: clker.com)
Q9: How is a compass used to find directions?

Answer: A magnetic compass consists of a small pointed magnet which is suspended freely. A freely suspended magnet always aligns in N-S direction. The red coloured magnetic needle points to North direction. Once we know North direction, we can easily find out the other directions.
E.g. If North is upwards, South is downward side, East will be on right hand side and West shall be on left hand side.


Q10: A magnet was brought from different directions towards a toy boat that has been floating in water in a tub. Affect observed in each case is stated in  Column I. Possible reasons for the observed affects are mentioned in Column II. Match the statements given in Column I with those in Column II.


Answer:

    Column I                  Column II      
Boat gets attracted towards the magnet     Boat is made of magnetic material    
Boat is not affected by the magnetBoat is made up non-magnetic material   
Boat moves towards the magnet if north
pole of the magnet is brought near its
head
Boat is fitted with a magnet with south
pole towards its head
Boat moves away from the magnet when
north pole is brought near its head
Boat is fitted with a magnet with north
pole towards its head
Boat floats without changing its direction.    Boat has a small magnet fixed along its
length


Q11: What is magnetite?

Answer: The natural magnet is called magnetite.

Q12: Name the place it is believed where natural magnet was found first time.

Answer: Magnesia in Ancient Greece.

Q13: How magnets were discovered?

Answer: There was a shepherd called Magnes who lived in Ancient Greece. He used to carry a stick with iron piece attached to it while taking his sheep for grazing to nearby mountains. One day he found his stick was attracted to a rock. This was the way he discovered natural magnet.

Q14: What are magnetic materials? Give two examples.

Answer: The materials which get attracted to magnets are known as
magnetic materials.
Examples are: Iron, Nickel, Cobalt

Q15: What are non-magnetic materials? Give examples.

Answer: The materials which do not get attracted to magnets are called non-magnetic materials.
Examples: Plastic, wood, paper

Q16: How do magnets loose their magnetic property?

Answer: Magnets lose their property on heating, hammering and dropping.

Q17: If a bar magnet is cut lengthwise into three parts, how many number of Poles will form?

Answer: Six (Three North and three south)


7 comments:

  1. very nice!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

    ReplyDelete
  2. actually the true and false one it is true it is discovered in Greece

    ReplyDelete