Magnetism - Science Doctor - Free Printable

Introduction to Magnetism

#### Basic

Q1. Magnetism is a contact/non-contact force.

- Answer: Non-contact force.

Magnetism is a non-contact force because it acts through the magnetic field without requiring physical contact between objects.

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Q2. What is the unit of a force?

- Answer: Newton (N).

The SI unit of force is the Newton (N), named after Sir Isaac Newton.

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Q3. Like poles ________, unlike poles _________.

- Answer: Like poles repel, unlike poles attract.

This is a fundamental property of magnets:
- Like poles (e.g., North-North or South-South) repel each other.
- Unlike poles (e.g., North-South) attract each other.

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Q4. What are the three magnetic metals?

- Answer: Iron, nickel, and cobalt.

These are the primary magnetic metals that can be magnetized.

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Q5. What is the name given to the type of magnet shown in the diagram to the right?

- Answer: Bar magnet.

The diagram shows a bar-shaped magnet with a uniform magnetic field around it, which is characteristic of a bar magnet.

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Q6. What are the lines on the diagram called?

- Answer: Magnetic field lines.

These lines represent the direction and strength of the magnetic field. They emerge from the North pole and enter the South pole.

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Q7. Make the North and South poles on the diagram on the right by writing N and S on the correct ends of the magnet.

- Answer: The diagram shows the magnetic field lines emerging from one end and entering the other. Based on this, the end where the lines emerge is the North pole (N), and the end where the lines enter is the South pole (S).

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#### Medium

Q8. Answer true/false for the below questions:

a) Magnets need to touch for them to be a force between them.
- False. Magnets exert forces on each other through their magnetic fields, even when they are not in contact.

b) A North pole will repel a South pole.
- False. A North pole attracts a South pole.

c) A North pole will attract a South pole.
- True. This is a fundamental property of magnets.

d) A South pole will attract a South pole.
- False. Unlike poles attract, so a South pole repels another South pole.

e) A South pole will attract a North pole.
- True. This is a fundamental property of magnets.

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Q9. Where is the magnetic field strongest by a bar magnet? Explain how we can tell this from the diagram above.

- Answer: The magnetic field is strongest near the poles of the bar magnet.

From the diagram:
- The magnetic field lines are closer together near the poles. This indicates a stronger magnetic field because the density of the field lines represents the strength of the field.
- The field lines spread out as they move away from the poles, indicating a weaker field.

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Q10. What is a permanent magnet?

- Answer: A permanent magnet is a material that retains its magnetic properties over a long period of time. It has a persistent internal magnetic field due to the alignment of its atomic dipoles.

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Q11. What is an induced magnet?

- Answer: An induced magnet is a material that becomes temporarily magnetized when placed in an external magnetic field. Once the external field is removed, the material loses its magnetism.

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Q12. Induced magnetism always causes a force of _____________.

- Answer: Attraction.

Induced magnetism occurs when a material aligns its magnetic domains in the direction of an external magnetic field, resulting in an attractive force between the material and the magnet.

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Q13. What do you see when you sprinkle iron filings around a magnet?

- Answer: When iron filings are sprinkled around a magnet, they align themselves along the magnetic field lines, forming visible patterns that trace the shape of the field. The filings cluster more densely near the poles, indicating the stronger field there.

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#### Hard

Q14. Which one of the metal bars is a piece of unmagnetized iron? Explain why.

- Answer: Bar C is the unmagnetized iron.

Explanation:
- Bars A, B, D, and F show attraction or repulsion, indicating they have magnetic poles.
- Bar C does not show any interaction (attraction or repulsion), suggesting it is unmagnetized and does not have aligned magnetic domains.

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Q15. Sketch magnetic field lines for when:

a) Two North poles of bar magnets are near each other.
- Answer: The field lines will point away from both North poles and repel each other. The lines will diverge and push apart.

b) Two South poles of bar magnets are near each other.
- Answer: Similar to part (a), the field lines will point toward both South poles and repel each other. The lines will diverge and push apart.

c) A North and a South pole of two bar magnets are near each other.
- Answer: The field lines will connect from the North pole to the South pole, showing attraction. The lines will converge and pull the magnets together.

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Q16. Explain some similarities and differences between:

a) Magnetism and gravity.
- Similarities:
- Both are non-contact forces.
- Both involve interactions between objects at a distance.
- Both follow inverse-square laws (the force decreases with the square of the distance).
- Differences:
- Gravity is always attractive, while magnetism can be either attractive or repulsive.
- Gravity acts between masses, while magnetism acts between magnetic poles.
- Gravity is much weaker than magnetism at short distances.

b) Magnetism and electrostatic forces.
- Similarities:
- Both are non-contact forces.
- Both involve interactions between charges/poles.
- Both follow inverse-square laws.
- Differences:
- Electrostatic forces act between electric charges, while magnetic forces act between magnetic poles.
- Electrostatic forces are always attractive or repulsive (like charges repel, opposite charges attract), while magnetic forces depend on the orientation of poles (like poles repel, unlike poles attract).
- Moving charges create magnetic fields, but stationary charges do not create magnetic fields.

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Final Answers:

1. Non-contact force.
2. Newton (N).
3. Repel, attract.
4. Iron, nickel, cobalt.
5. Bar magnet.
6. Magnetic field lines.
7. N and S labeled correctly based on field lines.
8. a) False, b) False, c) True, d) False, e) True.
9. Strongest near the poles; field lines are denser there.
10. Permanent magnet: retains magnetic properties.
11. Induced magnet: temporarily magnetized.
12. Attraction.
13. Iron filings align along field lines, clustering near poles.
14. Bar C is unmagnetized.
15. Field line sketches as described.
16. Similarities and differences explained.

Final Answer Box:
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