Maharashtra State Board Class 7 Science Properties of a Magnetic Field / Textbook Exercises and Extra Question and Answers.
Properties of a Magnetic Field Key Points:
Magnetic Alloys:
- Magnets are often made from alloys of iron, cobalt, and nickel.
- Nipermag is an alloy of iron, nickel, aluminum, and titanium used to make magnets.
- Alnico is a magnetic alloy of aluminum, nickel, and cobalt.
Earth as a Magnet:
- William Gilbert explained that a freely suspended magnet aligns in the north-south direction because the Earth itself is a giant magnet.
- He suspended a spherical magnet and observed its behavior when a bar magnet’s north pole was brought near it.
Magnetic Fields:
- Michael Faraday named the lines going from one end of a bar magnet to the other “magnetic lines of force.”
- The region around a magnet where magnetic force acts on an object is called a magnetic field.
- Magnetic field intensity is determined by the number of lines of force passing through a unit area.
- Magnetic attraction and repulsion occur through these lines of force.
- The intensity of the magnetic field is low where lines of force are sparse and high where they are concentrated.
Properties of Magnetic Lines of Force:
- Magnetic lines of force are imaginary lines introduced to explain magnetic attraction and repulsion.
- They run from the north pole to the south pole, whether it’s the same magnet or a different one.
- They are in a state of tension like a stretched spring.
- They repel each other.
- They do not intersect each other.
- The number of magnetic lines of force at a point determines the strength of the magnetic field there.
Metal Detectors:
- Metal detectors function based on electromagnets.
- They are used in various important places like airports, bus stations, temples, and buildings to inspect people entering these areas.
- Metal detectors are used in the food-processing industry to detect iron or steel objects in food, as they can be harmful to health.
- In geology, metal detectors are used to detect the presence and quantity of metals.
Write the appropriate term in the blanks.
(a) The alloys called Alnico and Nipermag are used for making industrial magnets.
(b) A magnetic field can pass through non-magnetic materials and vacuum.
(c) The intensity of a magnetic field is indicated by the lines of force.
(d) The real test of a magnet is its ability to attract iron or steel objects.
Short Questions and Answers:
Q: What are the common materials used to make industrial magnets?
A: Alnico and Nipermag are common alloys used to make industrial magnets.
Q: What can a magnetic field pass through?
