1. Observe pictures A and B given in fig 13.1 carefully.
Which of the following statements is correct for the above-given pictures?
(a) In A, cars 1 and 2 will come closer to each other and in B, 3 and 4 will move away from each other.
(b) In A, cars 1 and 2 will move away, and in B, 3 and 4 will come closer to each other.
(c) In A, cars 1 and 2 will move away from each other, and in B, cars 3 and 4 will move away.
(d) In A, cars 1 and 2 will come closer, and in B, cars 3 and 4 will come closer.
1. Observe pictures A and B given in fig 13.1 carefully.
Which of the following statements is correct for the above-given pictures?
(a) In A, cars 1 and 2 will come closer to each other and in B, 3 and 4 will move away from each other.
(b) In A, cars 1 and 2 will move away, and in B, 3 and 4 will come closer to each other.
(c) In A, cars 1 and 2 will move away from each other, and in B, cars 3 and 4 will move away.
(d) In A, cars 1 and 2 will come closer, and in B, cars 3 and 4 will come closer.
Explanation:
The correct option is (a) In A, cars 1 and 2 will come closer to each other and in B, 3 and 4 will move away from each other.
Magnets repel other magnets with the same pole (i.e., north repels north or south repels south) and attracts magnets with opposite poles. That’s why option (a) is correct.
All other options are wrong.
2. The arrangement to store two magnets is shown in figures (a), (b), (c) and (d) in fig below. Which one of them is the correct arrangement?
2. The arrangement to store two magnets is shown in figures (a), (b), (c) and (d) in fig below. Which one of them is the correct arrangement?
Explanation:
The correct option is (b) Wooden block between the magnets with metal plates at the ends and with opposite poles adjacent to each other.
The metal plates at the side will keep the magnets enclosed and the wooden block in between prevents the magnets from sticking to each other.
Options (c) and (d) are wrong because wooden blocks at the sides do not do anything and option (a) is wrong because like poles are adjacent to each other so there would be repulsive force between the magnets.
3. Three magnets A, B and C, were dipped one by one in a heap of iron filing. Figure 13.3 shows the amount of 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
3. Three magnets A, B and C, were dipped one by one in a heap of iron filing. Figure 13.3 shows the amount of 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
Explanation:
The correct answer is (c) A > B > C
The quantity of iron filings stuck to the magnets tells us about the strengths of the magnets.
As magnet A has the most fillings it is the strongest one.
And magnet C is the weakest one.
4. North pole of a magnet can be identified by
(a) Using iron filings.
(b) Using an iron bar.
(c) Another magnet, no matter whether the poles are marked or not.
(d) Another magnet having its poles marked as North pole and South pole.
4. North pole of a magnet can be identified by
(a) Using iron filings.
(b) Using an iron bar.
(c) Another magnet, no matter whether the poles are marked or not.
(d) Another magnet having its poles marked as North pole and South pole.
Explanation:
The correct option is (d) Another magnet having its poles marked as North pole and South pole.
The north pole of a magnet can be identified by using another magnet having its poles marked as North pole and South pole. When the north pole of one magnet is brought close to the marked south pole of another magnet, they will attract each other due to the opposite poles facing each other. And if the north pole of the first magnet is brought close to the north pole of the other magnet then they will repel each other.
5. A bar magnet is immersed in a heap of iron filings and pulled out. The amount of iron filing clinging to the
(a) Magnet will be the same all along its length.
(b) North pole is much less than the South Pole.
(c) North pole is much more than the South Pole.
(d) North Pole is almost equal to the South Pole.
5. A bar magnet is immersed in a heap of iron filings and pulled out. The amount of iron filing clinging to the
(a) Magnet will be the same all along its length.
(b) North pole is much less than the South Pole.
(c) North pole is much more than the South Pole.
(d) North Pole is almost equal to the South Pole.
Explanation:
The correct option is (d) North Pole is almost equal to the South Pole.
The magnetic field lines of a bar magnet emerge from its North Pole and merge into its South Pole.
But, both the north and south poles have almost equal strengths so, the amount of iron fillings at the north and south pole will be the same.
6. Fill up the empty spaces:
When a bar magnet is broken; each of the broken parts will have _________ pole(s).
In a bar magnet, magnetic attraction is _____ near its ends.
6. Fill up the empty spaces:
When a bar magnet is broken; each of the broken parts will have _________ pole(s).
In a bar magnet, magnetic attraction is _____ near its ends.
Explanation:
When a bar magnet is broken, each of the broken parts will have a north pole and a south pole.
In a bar magnet, magnetic attraction is strongest near its ends.
7. 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?
7. 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?
Explanation:
The reason Paheli could not collect the stainless steel pins using a magnet is that stainless steel is a non-magnetic material. Unlike materials such as iron, nickel, and cobalt, which are attracted to magnets, stainless steel does not have magnetic properties. Therefore, the magnet would not be able to attract or pick up the stainless steel pins.
8. Can you describe a method for verifying that "tea dust" is free of adulteration with iron powder?
8. Can you describe a method for verifying that "tea dust" is free of adulteration with iron powder?
Explanation:
To test if tea dust is adulterated with iron powder, we can perform the following simple experiment:
Take a small quantity of tea dust in a test tube.
Add water to the test tube and shake it well.
Place a magnet near the test tube and observe if any iron powder is attracted to the magnet.
If the tea dust is adulterated with iron powder, the iron particles will be attracted to the magnet, and we will be able to see them on the surface of the magnet. If no iron particles are attracted to the magnet, then the tea dust is not adulterated with iron powder.
9. 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 below.
(a) Which regions of the magnet have more iron filings sticking to it?
(b) What are these regions called?
9. 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 below.
(a) Which regions of the magnet have more iron filings sticking to it?
(b) What are these regions called?
Explanation:
(a) The regions at the ends of the bar magnet have more iron filings sticking to it.
(b) These regions are known as the poles of the magnet. Specifically, the end with the iron filings sticking to it is the magnetic north pole, and the other end is the magnetic south pole.
10. Four identical iron bars were dipped in a heap of iron filings one by one. The figure shows the amount of iron filings sticking to each of them.
(i) Which of the iron bars is likely to be the strongest magnet?
(ii) Which of the iron bars is not a magnet? Justify your answer.
10. Four identical iron bars were dipped in a heap of iron filings one by one. The figure shows the amount of iron filings sticking to each of them.
(i) Which of the iron bars is likely to be the strongest magnet?
(ii) Which of the iron bars is not a magnet? Justify your answer.
Explanation:
(i) The quantity of iron filings stuck to the magnets tells us about the strengths of the magnets.
And from the figure we can observe that (a) has the most fillings sticking to it.
Therefore, magnet (a) is the strongest one among them.
(ii) As from the figure we can see that magnet (b) has no iron fillings attached to it. So, magnet (b) must not be a magnet.
11. If a bar magnet is hidden inside a toy car along its length, how would you determine which pole of the magnet is facing the front of the car using another magnet?
11. If a bar magnet is hidden inside a toy car along its length, how would you determine which pole of the magnet is facing the front of the car using another magnet?
Explanation:
To figure out which pole of the hidden bar magnet is facing the front of the toy car, you can follow these steps:
Take a small magnet and bring it close to the front of the car without touching it.
Observe if the car moves towards or away from the small magnet.
If the car moves towards the north pole of the small magnet, the pole of the hidden magnet facing the front of the car is the south pole facing the front of the car.
If the car moves away from the north pole of the small magnet, the pole of the hidden magnet facing the front of the car is the north pole.
By observing the direction in which the car moves, we can determine the orientation of the hidden magnet inside the car.
12. Match the items in column I with the corresponding items in column II. (One option in A may match with more than one option in B.)
12. Match the items in column I with the corresponding items in column II. (One option in A may match with more than one option in B.)
Explanation:
13. If given two identical metal bars, one of which is a magnet, can you propose two methods to determine which one is the magnet?
13. If given two identical metal bars, one of which is a magnet, can you propose two methods to determine which one is the magnet?
Explanation:
Here are two ways to identify the magnet:
Hang the bars from a string: If you hang both the bars from a string, the magnet will orient itself in the north-south direction due to Earth's magnetic field, while the non-magnetic bar will hang in any random direction.
Use another magnet: If you have a known magnet, you can use it to identify the magnet bar. Bring one end of the magnet near one end of each metal bar. The magnet will either be attracted or repelled by the magnet bar, whereas it will not have any effect on the non-magnetic bar. By comparing the behavior of the two bars, you can identify the magnet.
14. There are three identical iron bars placed on a table, out of which two are magnets, and one of the magnets has marked North-South poles. How would you determine which of the remaining two bars is a magnet and identify its pole(s)?
14. There are three identical iron bars placed on a table, out of which two are magnets, and one of the magnets has marked North-South poles. How would you determine which of the remaining two bars is a magnet and identify its pole(s)?
Explanation:
To identify which of the other two bars is a magnet, we can use the known magnet with marked poles.
Here are the steps to follow:
Bring one end of the known magnet near one end of the first iron bar on the table. If it attracts or repels the bar, then it is a magnet. If it doesn't have any effect, then it is non-magnetic. Note down the result.
Repeat step 1 with the second iron bar on the table.
Now, we know which one of the two bars is the magnet. Take the magnet and bring one end of it near one end of the remaining iron bar on the table. If it attracts or repels the bar, then it is the second magnet. If it doesn't have any effect, then it is non-magnetic.
To identify the poles of the newly identified magnet, we can use the known magnet again:
Bring one end of the known magnet near one end of the new magnet. If they attract each other, then the marked pole of the new magnet is opposite to the pole of the known magnet that is attracting it. If they repel each other, then the marked pole of the new magnet is the same as the pole of the known magnet that is repelling it.
Flip the known magnet and repeat step 1. This will help confirm the pole orientation of the newly identified magnet.
15. Can you explain the process of magnetizing an iron strip using a magnet and list the necessary steps involved?
15. Can you explain the process of magnetizing an iron strip using a magnet and list the necessary steps involved?
Explanation:
Here are the steps to magnetize an iron strip with the help of a magnet:
Take a magnet and an iron strip. The iron strip should be made of a ferromagnetic material, such as iron or steel.
Rub the magnet against the iron strip in one direction, starting from one end of the strip and moving towards the other end. The direction of rubbing should be consistent and in the same direction throughout.
Repeat the rubbing process several times, moving the magnet back and forth along the same path each time. This process will help align the domains in the iron strip in the same direction.
After rubbing for some time, the iron strip will become magnetized. You can test its magnetism by bringing it near iron filings or another ferromagnetic material. The iron strip should attract these materials if it is magnetized.
Note: It is important to rub the magnet in one direction only to ensure that the domains in the iron strip align in the same direction. If you rub the magnet in multiple directions, the domains will not align properly, and the iron strip may not become magnetized.
16. Figure below 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.
16. Figure below 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.
Explanation:
If you bring a bar magnet near a needle of a magnetic compass then the needle of the compass will get deflected or attracted according to the orientation of the bar magnet.
17. Can you propose a procedure for creating a magnetic compass using an iron needle and a bar magnet?
17. Can you propose a procedure for creating a magnetic compass using an iron needle and a bar magnet?
Explanation:
Here is an activity to prepare a magnetic compass using an iron needle and a bar magnet:
Materials Required:
An iron needle
A bar magnet
A cork or a small piece of polystyrene foam
A bowl of water
Steps:
Rub the bar magnet repeatedly against one end of the iron needle, in the same direction, to magnetize it.
Cut a small piece of cork or polystyrene foam and place it in the bowl of water.
Float the magnetized iron needle on the surface of the water using the cork or polystyrene foam. Make sure the needle is floating freely and not touching the sides or bottom of the bowl.
Wait for a few seconds until the needle comes to rest and the cork or polystyrene foam stops moving. The iron needle will align itself in the north-south direction due to the Earth's magnetic field, with one end pointing towards the North and the other towards the South.
Mark the end of the iron needle pointing towards the North with a pen or a marker. This end of the needle is the North pole of the compass.
Your magnetic compass is now ready to use. You can use it to find the direction of North, South, East, and West.
Note: Make sure the bowl of water is placed on a flat surface and there are no nearby sources of magnetic interference such as electronic devices or metal objects. Also, keep the bar magnet away from any electronic devices as it can interfere with their operation.
18. Boojho kept a magnet close to an ordinary iron bar. He observed that the iron bar attracts a pin, as shown in fig below.
What inference could he draw from this observation? Explain.
18. Boojho kept a magnet close to an ordinary iron bar. He observed that the iron bar attracts a pin, as shown in fig below.
What inference could he draw from this observation? Explain.
Explanation:
Boojho's observation that an ordinary iron bar attracts a pin when a magnet is kept close to it indicates that the iron bar has become magnetized by induction.
When a magnet is brought close to an iron bar, it creates a magnetic field around the bar. This magnetic field causes the domains in the iron bar to align in the direction of the magnetic field. As a result, the iron bar becomes magnetized temporarily.
This observation demonstrates the concept of magnetic induction, which is the process of inducing magnetism in a material by exposing it to a magnetic field. It is a fundamental concept in electromagnetism and is used in many applications, such as in the operation of transformers, generators, and electric motors which you will study in higher classes.
19. A bar magnet is cut into two pieces, A and B, from the middle, as shown in figure below.
Will the two pieces act as individual magnets? Mark the poles of these two pieces. Suggest an activity to verify your answer.
19. A bar magnet is cut into two pieces, A and B, from the middle, as shown in figure below.
Will the two pieces act as individual magnets? Mark the poles of these two pieces. Suggest an activity to verify your answer.
Explanation:
Yes, the two pieces will act as individual magnets, each with its own North and South poles.
When a bar magnet is cut in half, each piece becomes a smaller magnet, with its own North and South poles. The magnetic field strength will decrease since the size of the magnet has decreased, but the two pieces will still have their own poles and will attract or repel other magnets accordingly.
To verify this, you can perform a simple experiment by using a small compass. Place the two pieces of the magnet on a table, and place the compass nearby. Move the compass around the pieces of the magnet and observe how the needle of the compass reacts. You will notice that the needle will point towards the North pole of one of the pieces, and towards the South pole of the other piece. This shows that each piece of the magnet has its own North and South poles, and is indeed acting as a separate magnet.
20. Can you propose a method for organizing a U-shaped magnet? How does this differ from organizing a pair of bar magnets?
20. Can you propose a method for organizing a U-shaped magnet? How does this differ from organizing a pair of bar magnets?
Explanation:
These are the following arrangements to store bar and U-shaped magnet:
U-shaped magnet: A metal plate attached to both ends of the poles of the U-shaped magnet.
Bar magnet: Wooden block between the magnets with metal plates at the ends and with opposite poles adjacent to each other.
The arrangement for storing a U-shaped magnet is different from storing a pair of bar magnets because of the shape and design of the magnets. U-shaped magnets are designed to provide a concentrated and strong magnetic field between the two poles, while bar magnets have a more uniform magnetic field along their length. As a result, the best way to store them to maintain the strength of the magnetic field is different.
