NCERT Exemplar Problems Class 6 Science – Fun with Magnets
Observe the pictures A and B given in figure carefully.
Which of the following statements is correct for the above given pictures?
(a) In A, cars 1 and 2 will come closer and in B, cars 3 and 4 will come closer.
(b) In A, cars 1 and 2 will move away from each other and in B, cars 3 and 4 will move away.
(c) In A, cars 1 and 2 will move away and in B, 3 and 4 will come closer to each other.
(d) In A, cars 1 and 2 will come closer to each other and in B, 3 and 4 will move away from each other.
(d) In A, cars 1 and 2 will come closer to each other because North and South poles (i.e. opposite poles) attract each other while in S, cars 3 and 4 will move away from each other because South poles (i.e. similar poles) repel each others
The arrangement to store two magnets is shown by figures (a), (b), (c) and (d) in figure. Which one of them is the correct arrangement?
(b) The correct arrangement is shown in option (b). To store the two magnets safely, they should be kept in pairs with their unlike poles on the same side. They must be separated by a piece of wood, while two metal plates should be placed across their ends.
Three magnets A, B and C were dipped one by one in a heap of iron filings.
Figure shows the amount of the iron filings sticking to them.
The strength of these magnets will be
(a) A > B > C (b)A < B < C
(c) A = B = C (d )A < B > C
(a) As we can see from the diagram that amount of iron filings in A is greater than B and C and in 8, it is greater than C. So, the strength of magnets will be according to the amount of iron filings sticking to them only.
North pole of a magnet can be identified by
(a) another magnet having its poles marked as North Pole and South pole
(b) another magnet no matter whether the poles are marked or not
(c) using an iron bar
(d) using iron filings
(a) North pole (South pole) can be identified only if we have another magnet having its poles marked as North pole and South pole because only then we can see the attraction and repulsion between N-S (i.e. opposite) poles and N-N (i.e. similar) poles, respectively.
A bar magnet is immersed in a heap of iron filings and pulled out. The amount of iron filings clinging to the
(a) North pole is almost equal to the South pole
(b) North pole is much more than the South pole
(c) North pole is much less than the South pole
(d) magnet will be same all along its length
(a) The amount of iron filings clinging to the North pole is almost equal to the South pole because in a magnet, the strength of both the poles is same.
Very Short Answer Type Questions
Fill in the blanks
(i) When a bar magnet is broken, each of the broken part will have pole/poles.
(ii) In a bar magnet, magnetic attraction is near its ends.
(i) Two; When a bar magnet is broken, each of the broken part will behave as a magnet having two magnetic poles, North and South.
(ii) Strong; In a bar magnet, magnetic attraction or its strength is maximum at poles and minimum at the centre.
Paheli and her friends were decorating the class bulletin board. She dropped the box of stainless steel pins by mistake. She tried to collect the pins using a magnet. She could not succeed. What could be the reason for this?
She could not succeed because the stainless steel pins are not made of iron, i.e. they are non-magnetic, so they are not attracted towards magnet.
How will you test that ‘tea dust’ is not adulterated with iron powder?
We can do a simple experiment for this:
(i) Take tea dust on a paper.
(ii) Take a bar magnet in your hand.
(iii) Place the bar magnet over this dust.
(iv) If some particles are attracted strongly towards this magnet by clinging to it, then definitely tea dust will have iron powder.
Boojho dipped a bar magnet in a heap of iron filings and pulled it out. He found that iron filings got stuck to the magnet as shown in figure.
(a) Which regions of the magnet have more iron filings sticking to it?
(b) What are these regions called?
(a) The two ends of the magnet have more iron filings sticking to it because magnetic strength is maximum near the ends of the magnet.
(b) These ends are called poles of the magnet (i.e. North and South poles of magnet).
Short Answer Type Questions
Four identical iron bars were dipped in a heap of iron filings one by one. Figure shows the amount of iron filings sticking to each of them.
(a) Which of the iron bar is likely to be the strongest magnet?
(b) Which of the iron bar is not a magnet? Justify your answer.
(a) Iron bar (i) seems to be the strongest magnet because the maximum amount of iron
filings are sticking to it, i.e. maximum iron filings have been attracted by it.
(b) Iron bar (ii) is not a magnet because no iron filings have been attracted by it.
A toy car has a bar magnet laid hidden inside its body along its length. Using another magnet, how will you find out which pole of the magnet is facing the front of the car?
If we face North pole of a magnet towards the front side of the car and the car is attracted, it means its front side pole is South pole and if it is going away, it means its front side is North pole.
Match the Column I with Column II (one option of I can match with more than one option of II).
(a)- (ii), (iii) and (iv)
A magnet can attract magnetic materials like iron, iron filings and another magnet.
(b) – (iii)
If the North pole of a magnet is brought near the North pole of another magnet, then they both repel each other. Similarly, S-S poles of two magnets repel each other.
(c) – (i)
A magnet always stops in a particular direction (N-S), if suspended freely from a thread from its centre.
(d) – (iii)
Poles of a magnet can be identified only if we have another magnet having its poles marked as North pole and South pole because only then we can see the attraction and repulsion between N-S poles and N-N poles, respectively.
You are provided with two identical metal bars. One out of the two, is a magnet. Suggest two ways to identify the magnet.
The two ways to identify the magnet are
(i) Suspend the metal bars having their levels horizontal with a thread one by one. Let the metal bar come to rest.
Now, if we move it by pushing it slowly in any direction, then it will return to the same direction. This means that it is a magnet otherwise it is simply an iron bar.
(ii) Take some iron filings and move the iron bars over these iron filings one by one. If iron filings are attracted very strongly at poles, then it is a magnet and if they are not attracted, then it is simply an iron bar.
Long Answer Type Questions
Three identical iron bars are kept on a table. Two out of three bars are magnets. In one of the magnets the North-South poles are marked. How will you find out which of the other two bars is a magnet? Identify the poles of this magnet.
To find out the magnet:
(i) Take the bar magnet with known poles in your hand.
(ii) Take one of the other two iron bars in other hand.
(iii) Bring one side of iron bar towards the South pole of the bar magnet and note down whether it is attracted or repelled.
(iv) Bring other side of iron bar towards the South pole of the bar magnet and again note down the same thing.
(v) If there is an attraction in both cases (iii) and (iv), then it is definitely a simple iron bar.
(vi) If there is an attraction in one case and repulsion in other case, then it is a bar magnet.
(vii) Do the same for the third iron bar.
To find out the poles:
If in case (iii), the bar is attracted, then it is North pole of the identified bar magnet. If the bar is repelled, then it is obviously a South pole of the identified bar magnet.
Describe the steps involved in magnetising an iron strip with the help of a magnet.
Steps involved in magnetising an iron strip are:
(i) Take an iron strip which is to be magnetised.
(ii) Keep it on a wooden table.
(iii) Hold one end of a bar magnet in your hand and keep the other end of bar magnet near one edge of iron strip.
(iv) Without lifting, move it along the length of iron strip till you reach the other edge.
(v) After reaching the end of iron strip, lift the bar magnet and bring it to the same position and repeat the process again and again.
(vi) Bring some iron filings near the iron strip to check whether it has become a magnet. If not, continue the same process for some more time.
Given below is a figure which shows a magnetic campass. Briefly explain what will happen to the position of its needle if you bring a bar magnet near it? Also, draw a diagram to show the effect on the needle on bringing the bar magnet near it. Also, draw the diagram to show the effect when the other end of the bar magnet is brought near it.
If we bring a bar magnet near a magnetic compass N, its needle will get deflected.
When we bring North pole of a bar magnet near the magnetic compass, its needle will be deflected away from the magnet as shown in Fig. (i). However, when we bring South pole of bar magnet near the magnetic compass, needle will be deflected towards the magnet as shown in Fig. (ii).
Suggest an activity to prepare a magnetic compass by using an iron needle and a bar magnet.
Steps involved in preparing a magnetic compass are :
(i) Take an iron needle which is to be magnetised.
(ii) Magnetise it using a bar magnet.
(iii) Insert the magnetised needle through a small piece of cork.
(iv) Let the cork float in a water in a bowl. Make sure that the needle does not touch the water.
(v) Your magnetic compass is now ready to work. Note the direction in which the needle points when the cork is floating.
(vi) Rotate the cork, with the needle fixed in it, in different directions. Note the direction in which the needle points when the cork begins to float again without rotating.
You will observe that the needle indicates the North-South direction when it comes to rest.
Boojho kept a magnet dose to an ordinary iron bar. He observed that the iron bar attracts a pin as shown in figure.
What inference could he draw from this observation? Explain.
When we place any iron bar near a bar magnet, the magnetic properties are induced in it and it acts like a magnet. The small objects like pin, iron filings can be attracted by it. But when we remove the bar magnet kept near it, it again becomes an iron bar and does not attract the small iron objects.
A bar magnet is cut into two pieces A and B from the middle as shown in figure.
Will the two pieces act as individual magnets? Mark the poles of these two pieces. Suggest an activity to verify your answer.
Yes, the two pieces will work as individual magnets because a monopole (single pole) of magnet never exists.
(i) Place the magnet, so formed (A and B) on the table.
(ii) Bring the North pole of both magnets towards each other, they will be repelled.
(iii) Bring the North and South poles of both magnets towards each other, they will attract.
This proves that the two pieces will act as individual magnets having attraction and repulsion properties.
Suggest an arrangement to store a U-shaped magnet. How is this different from storing a pair of bar magnets?
It is a suggested way shown in figure below :
U-shaped magnet is kept along with an iron piece across its two poles, while a pair of bar magnets is kept along with iron strips and magnets separated by wood along their length as shown in above figure.