Olympiad Test: Fun With Magnets -2 - Class 6 MCQ

The question involves identifying object P based on its attraction to the south pole of a bar magnet. Here's a step-by-step explanation:

1. Understanding Magnetism:

   • A bar magnet has two poles: North (N) and South (S).
   • Like poles repel, and opposite poles attract.
   • Materials like iron, nickel, and cobalt are magnetic and can be attracted to magnets. Copper, on the other hand, is non-magnetic.

2. Observation:

   • The end marked Z of object P is attracted to the South Pole of the bar magnet.

3. Possible Scenarios:

   • If P contains a magnet, its North Pole would be attracted to the South Pole of the bar magnet.
   • If P contains a nickel rod, it can also be attracted to the magnet since nickel is a magnetic material.
   • A copper rod would not be attracted because copper is non-magnetic.

4. Answer Choices:

   • A: Copper rod and magnet — Incorrect, because copper is non-magnetic.
   • B: Nickel rod and Copper rod — Incorrect, because a copper rod alone cannot be magnetic.
   • C: Magnet and Nickel rod — Correct, because both can explain the attraction to the South Pole of the bar magnet.
   • D: None of the above — Incorrect, as option C fits.

The correct answer is C: Magnet and Nickel rod, because these materials can explain why the object is attracted to the South Pole of the bar magnet.

Michael's Experiment:

1. Setup:

   • A magnet is used to attract nails.
   • A plastic sheet is placed between the magnet and the nails.
   • Additional plastic sheets are gradually added until the nails are no longer attracted to the magnet.

2. Observation:

   • As more plastic sheets are added, the magnetic force weakens and eventually cannot reach the nails.

Aim of the Experiment: The aim is to find out the strength of the magnet by testing how many plastic sheets it can pull the nails through. The strength of the magnet is determined by its ability to exert force through increasing barriers.

Answer Choices:

• A: To find out if the plastic is magnetic — Incorrect, as the experiment doesn't test the magnetic properties of plastic.
• B: To find out if the nails are magnetic — Incorrect, because the nails' magnetic properties are already known (they are attracted to the magnet).
• C: To find out the strength of the magnet — Correct, as the experiment determines how far the magnet's force can act.
• D: To find out the part of the magnet that has the strongest pull — Incorrect, because this experiment does not focus on the magnet's poles or specific regions.

Correct Answer: C: The aim of the experiment is to find out the strength of the magnet.

In this scenario, Sahil uses a magnet to pull the iron disc out of the tank. The correct explanation for why the magnet was able to pull the iron disc from the tank involves understanding how magnetism works:

• Magnetic Properties: Magnets can attract ferromagnetic materials (like iron, cobalt, and nickel). The iron disc is made of a ferromagnetic material, which is why the magnet was able to attract and move it.
• Non-magnetic Materials: Both oil and plastic are non-magnetic materials. These substances do not become magnetized when exposed to a magnetic field. The magnetic field, however, can pass through these materials without being affected.
• The Role of the Magnet: The magnet does not need to directly contact the iron disc (though it likely did). It can exert a magnetic force through the oil and plastic tank, which is why it was able to pull the iron disc out even though it's submerged in oil and behind the plastic tank.

Thus, magnetism can pass through the oil and plastic tank without being significantly weakened by these materials, making D the correct option.

A magnet can lose its magnetism through a few methods, most notably:

• Using it as a hammer (Option C): Striking a magnet with force, such as using it as a hammer or dropping it onto a hard surface, can cause its atoms to lose alignment. This disrupts the magnetic field and weakens or even demagnetizes the magnet.

Why other options are incorrect:

• A: Playing with it: Simply playing with a magnet (without striking or damaging it) does not typically weaken its magnetism. It may lose its strength over time, but playing with it alone is not enough to make it weaker.

• B: Keeping it wrapped in a cotton cloth: Keeping a magnet in a cotton cloth will not affect its magnetism. It will remain protected from external factors, but the cloth itself does not impact the magnet's strength.

• D: Keeping it in a cool room: A cool room will not affect the strength of a magnet. In fact, magnets generally retain their strength in cool conditions, whereas heat (especially extreme heat) can demagnetize a magnet.

Therefore, the correct answer is C: Using it as a hammer.

Floppy disks store data using magnetic material on their surface. When a magnet is placed near a floppy disk, it can interfere with the magnetic fields that store the data on the disk. This interference can erase or corrupt the information, as the magnet's field can alter the alignment of the magnetic particles, disrupting the stored data.

Why other options are incorrect:

• A: Because the magnet will break the disk: Magnets do not break floppy disks. The physical structure of the disk is not affected by the presence of a magnet, but the data stored on it can be damaged.
• B: Because the magnet will rust: Magnets typically do not rust easily, especially the types used in consumer products like floppy disks. Rusting is more related to the material's exposure to moisture, not magnetic fields.
• C: Because the magnet will become weaker: The magnet will not weaken by being near a floppy disk. While prolonged exposure to certain conditions (like heat or other strong magnetic fields) may weaken a magnet, simply being near a floppy disk won't affect the magnet’s strength.

Thus, the correct answer is D: Because the information in the disk may be erased.

Magnets are often used in place of locks or bolts in household items like doors, cabinets, and appliances because they allow for easy opening and closing. Magnets provide a convenient way to secure doors or lids without the need for manual locking and unlocking mechanisms. This facilitates frequent usage as they can be opened and closed with minimal effort, and they still keep things in place.

Why the other options are incorrect:

• A: Ensure safety: While magnets may be used for security purposes, the primary reason for their use in doors or closures is ease of access and convenience, not safety. Locks are more commonly used for safety.

• B: Make the articles look beautiful: Magnets in closures are primarily functional, not aesthetic. Their use is focused on convenience and ease, not decoration.

• D: Make the articles airtight: While magnets may provide a good seal, their main purpose is not necessarily to create an airtight closure. Airtight seals are more commonly achieved with gaskets or seals, not magnets.

Thus, the correct answer is C: Facilitate frequent usage.

• A: Radio: Radios contain magnets, especially in the speaker or receiver, which are used to convert electrical signals into sound and capture radio waves.
• B: Fan: Fans have motors with magnets that are essential for converting electrical energy into mechanical energy to rotate the blades.
• C: Torch: While torches may have electrical components, such as a battery, bulb, or switch, they typically do not contain permanent magnets in their basic design. However, rechargeable models with magnetic charging might contain magnets, but in general, regular flashlights do not have magnets in their working mechanism.

Since C: Torch typically does not contain a magnet in its regular design, it is the correct answer.

• A: Using compass: A compass is used to detect the direction of the Earth's magnetic field, not for separating mixtures. It is not suitable for separating sand and iron filings.
• B: Filtration: Filtration is typically used to separate solid particles from liquids or solutions, but it is not effective for separating a mixture of sand and iron fillings since both are solid.
• C: Sedimentation: Sedimentation involves allowing particles to settle down in a liquid due to gravity, which is not relevant when dealing with a mixture of two solids.
• D: Magnetic separation: This is the most effective method for separating a mixture of sand (which is non-magnetic) and iron filings (which are magnetic). Using a magnet, you can easily attract the iron fillings, leaving the sand behind.

D: Magnetic separation is the best method for separating a mixture of sand and iron filings.

The mariner's compass was first invented by the Chinese during the Song Dynasty (around the 11th century). Initially, it was used for navigation on land and later adapted for maritime use. The compass was made using a magnetized needle that would align itself with the Earth's magnetic field, providing sailors with a reliable way to navigate.

• A: Indians: While Indians made significant contributions to science and mathematics, the invention of the mariner's compass is credited to the Chinese.

• B: Europeans: Europeans later adopted the compass for their navigation, but they did not invent it.

• D: Egyptians: Ancient Egyptians were known for their advancements in various fields, but they were not involved in the invention of the compass.

The mariner's compass was first invented by the Chinese.

When a magnet is placed in iron powder and then removed, the iron powder tends to gather more at the ends (poles) of the magnet. This is because the magnetic field is strongest at the poles of the magnet, which are the points where the magnetic forces are concentrated. The iron particles are attracted most strongly to the areas where the magnetic field is the most intense, which is at the north and south poles of the magnet.

• A: North pole only: Iron powder will not collect only at the north pole. Both poles of the magnet attract iron powder.
• B: South pole only: Similarly, iron powder will also gather at the south pole, not just the north or south exclusively.
• C: The middle of the magnet: The magnetic field is weakest at the center of the magnet, so iron powder will not gather there in large amounts.

The maximum amount of iron powder will be found at the ends of the magnet, where the magnetic field is the strongest.