🧲 Chapter 19 – Properties of a Magnetic Field

📘 Maharashtra Board Textbook Solutions – Standard Seven

📝 1️⃣ Fill in the Blanks

(a) The alloys called alnico and nipermag are used for making industrial magnets.

(b) A magnetic field can pass through water and cardboard.

(c) The intensity of a magnetic field is indicated by the lines of force.

(d) The real test of a magnet is repulsion.

🔗 2️⃣ With Whom Should I Pair Up? (Match the Pairs)

Group ‘A’Group ‘B’
(a) Compass(4) A magnetic needle
(b) Door of a cupboard(3) A magnet
(c) Repulsion(2) Like poles
(d) Magnetic pole(1) The highest magnetic force

❓ 3️⃣ Answer the Following Questions

(a) Distinguish Between the Two Methods of Making Artificial Magnets

Single Touch MethodDouble Touch Method
Magnetic strength produced is low.Magnetic strength produced is higher.
Magnetism lasts for a shorter time.Magnetism lasts for a longer time.
Only one magnet is used for stroking.Two magnets are used simultaneously.

(b) Substances Used for Making an Electromagnet

To make an electromagnet, we need:

  1. 🔌 A long conducting copper wire
  2. 🔩 An iron nail (core)
  3. 🔘 A switch
  4. 🔋 A battery

When electric current flows through the coil wound around the iron nail, it behaves like a magnet.

(c) Write a Note on “Magnetic Field”

  • The concept of magnetic lines of force was proposed by Michael Faraday.
  • The space around a magnet where its magnetic force can be experienced is called a magnetic field.
  • Magnetic field lines show the pattern and strength of magnetism.
  • These lines help us understand how magnetic force acts around a magnet.

(d) Why is a Magnetic Needle Used in a Compass?

  • A magnetic needle can rotate freely.
  • It always settles in the north-south direction due to Earth’s magnetism.
  • Once the north direction is known, other directions can be easily determined.

👉 Therefore, a magnetic needle is used in a compass to find directions.

(e) Explain with the help of a diagram How the Intensity and Direction of the Magnetic Field of a Bar Magnet are Determined

📌 Intensity of Magnetic Field

  1. Shown by the number of magnetic lines of force.
  2. More concentrated lines → Stronger magnetic field.
  3. Field strength is highest near the poles of the magnet.

📌 Direction of Magnetic Field

  1. Magnetic lines of force always start from the North Pole.
  2. They end at the South Pole.
  3. Hence, the direction of the magnetic field is from North to South (outside the magnet).

(f) How Did Merchants of Olden Times Use a Magnet While Travelling?

  • Merchants carried a compass during travel.
  • The compass had a freely rotating magnetic needle.
  • The needle always pointed in the north-south direction.
  • This helped travelers determine directions easily.
  • It was especially useful in deserts and oceans, where landmarks were not visible.

👉 Thus, magnets played an important role in navigation in ancient times.

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