Observe the pictures A and B given in Fig. 13.1 carefully.
Which of the following statement 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.
As we know unlike poles attract each other & like poles repel each other. So, in A, two cars are facing each other such that unlike poles are closer to each other. Therefore car 1 & car 2 will come closer. But in B, like poles are facing each other and will therefore repel that is move away from each other.
The arrangement to store two magnets is shown by figures (a), (b), (c) and (d) in Fig. 13.2. Which one of them is the correct arrangement?
A. Figure (a)
B. Figure (b)
C. Figure (c)
D. Figure (d)
With time magnets lose their magnetic properties. So in order to retain their magnetic strength, the pair of magnets is kept with unlike poles in the same direction with a wooden block between them and metal plates made up of soft iron are placed across the poles as shown in figure (b). This arrangement preserves the magnetic strength of magnets by completing the magnetic circuit.
Three magnets A, B and C were dipped one by one in a heap of iron filing. Fig. 13.3 shows the amount of the iron filing 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
As we can see from the given figure, A attracts more iron fillings followed by magnet B. Magnet C hardly attracts any iron filings. From the level of attraction of iron fillings we can definitely say that strength of A is more than B & strength of B is more than C.
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.
It will be easy for us to identify the north pole of a magnet (1) with the help of another magnet (2) whose North Pole & South Pole are marked as if we bring North pole of the magnet (2) to the poles of magnet (1), then the pole which will repel is the North pole of magnet (1).
A bar magnet is immersed in a heap of iron filings and pulled out. The amount of iron filling 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.
Poles have the maximum magnetic strength of equal intensity. Therefore, the amount of iron fillings attracted to both the boles will be almost equal.
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) When a bar magnet is broken; each of the broken part will have two pole/poles.
When the magnet is broken then each part of the broken magnet will develop its own North & South Pole.
(ii) In a bar magnet, magnetic attraction is more/greater near its ends.
North & South Pole have magnetic strength greater than the rest part of the magnet.
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?
Magnet attracts only those metals which have magnetic properties in them like iron, nickel, cobalt and so on. Here the pins are made up of stainless steel which is non-magnetic in nature. Therefore, the pins will not be attracted towards the magnet.
How will you test that ‘tea dust’ is not adulterated with iron powder?
It can be tested whether tea dust is adulterated with iron powder or not if we use a magnet. We move the magnet over the tea dust then if it’s adulterated, iron powder will be attracted to the magnet and if it’s not then magnet will come out clean.
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 Fig. 13.4.
(i) Which regions of the magnet have more iron filings sticking to it?
(ii) What are these regions called?
(i) The two ends of the magnet will have more iron fillings sticking to it as they have the maximum magnetic strength.
(ii) These regions are called North Pole & South Pole
Four identical iron bars were dipped in a heap of iron filings one by one. Fig. 13.5 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 bars is not a magnet? Justify your answer.
(a) In the given figure we can see that the iron bar in figure (a) attracts the maximum iron fillings. There (a) is the strongest magnet.
(b) Iron bar (b) is not a magnet as it does not attract any iron fillings.
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?
To determine which pole of the magnet is facing the front of the car, use another magnet whose North & South pole is marked. Now bring any pole, say North Pole of the magnet towards the magnet which is facing the front of the car. If they repel, then it is North Pole which is facing the front and if they get attracted, then it’s South Pole which is facing the front of the car.
Match Column I with Column II (One option of A can match with more than one option of B)
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 are:
● Put both the metal bars in the heap of iron fillings and bring them out. The one which attracts the iron fillings will be the magnet.
● Bring another magnet towards both the metal bars. The metal bar which attracts/repel the magnet is itself a magnet.
Three identical iron bars are kept on a table. Two out of three bars are magnets. In one of the magnet 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.
We can find the other magnet with the help of magnet in which North & South poles are marked. Bring the marked magnet closer to the other two iron bars. Both the bars will be attracted towards the magnet as they are both made up of iron. So to test magnet, repulsion of like poles are to be used. Bring the poles of iron bars one by one towards the north pole of the magnet. The iron bar will be attracted but the actual magnet can get attracted or get repelled. Now change the poles of the iron bars. The magnet will be attracted/repelled but the iron will only be attracted.
Describe the steps involved in magnetizing an iron strip with the help of a magnet.
The steps involved in magnetizing an iron strip with the help of magnet are:
● Place the iron strip which is to be magnetized on a wooden table.
● Take a bar magnet in such a manner that one end of the magnet is held in the hands and the other end is on one edge of the strip.
● Move the magnet, without lifting, along the length of the strip till the other edge is reached.
● Repeat the above steps several times.
● Bring the iron fillings and spread it on the strip. If it gets attracted the the strip gets magnetized and if it’s not then repeat the steps few more times.
Fig. 13.6 shows a magnetic compass. What will happen to the position of its needle if you bring a bar magnet near it? 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.
As magnetic compass is made up of magnet only so it will follow the magnetic properties. When North Pole of the magnet is brought near the compass, then North Pole of the compass will deflect/repel and South Pole of the compass will be attracted to the magnet. If we bring South Pole of the magnet towards the compass then North Pole of the compass will be attracted & South Pole will be deflected.
Suggest an activity to prepare a magnetic compass by using an iron needle and a bar magnet.
Steps to make a magnetic compass:
● Place the needle on a wooden table.
● Rub the magnet across its length without lifting it.
● Once the end point of needle is reached, lift the magnet and again rub it in the same direction.
● Remember not to change the direction and repeat the steps a dozen times.
● Now place the needle on the cork in a vessel containing water.
● The needle will move and align itself in the North-South direction.
Boojho kept a magnet close to an ordinary iron bar. He observed that the iron bar attracts a pin as shown in Fig. 13.7.
The iron bar can be used as a magnet as it has induced some magnetic properties from the bar magnet present there. The pin cannot be used as a magnet as it has very small area and as it is not in direct contact with the magnet, the magnetic strength is very less. Therefore it cannot induce magnetic properties.
Steps to show that they have/have not induced magnetic properties are:
● Place the iron bar & pin on the table just after it is being separated from the magnet.
● Now use iron fillings and spread it over the iron bar and the pin.
● We will infer that iron bar attracts some iron fillings but not the pin.
A bar magnet is cut into two pieces A and B, from the middle, as shown in Fig. 13.8.
Will the two pieces act as individual magnets? Mark the poles of these two pieces. Suggest an activity to verify your answer.
A magnet can be considered as a combination of smaller magnetic dipoles.
When we break a magnet into two halves lengthwise these dipoles get separated and act as individual magnets.
So, yes the two pieces will act as individual magnets.
The poles of new magnets can be detected by using a compass or by test of repulsion between newly formed magnets.
So new poles are marked as:
Suggest an arrangement to store a U shaped magnet. How is this different from storing a pair of bar magnets?
A U magnet is stored in a wooden box with a soft iron placed at the edge. A bar magnet is kept in pairs with opposite poles facing the same direction and separated by a wooden block. The two edges of the magnet are joined by soft iron bar.