Std 7 Science Chapter : Properties of magnetic field

Title : Std 7 Science Chapter : Properties of magnetic field

Magnetism II. Earth: A gigantic magnet III. Magnetic needle IV. Magnetic field V. Properties of magnetic lines of force VI. Penetrating ability of the magnetic field VII. Metal detector

Maharashtra state board solutions for class 7 SSC board science part STD 7-  science Properties of magnetic field

 Know everything about Properties of magnetic field Maharashtra state board class 7 SSC .Get detailed Questions and answers for chapter Science Magnetism II. Earth: A gigantic magnet III. Magnetic needle IV. Magnetic field V. Properties of magnetic lines of force VI. Penetrating ability of the magnetic field VII. Metal detector

Important questions and answers

*Q.1) Where and how are magnets used in our houses and our surroundings?

 Answer: Magnets are used in daily life like fridge magnets, magnetic cabinet, audio speakers, electric motors, computers hard drive has a number of magnets, etc.

 *Q.2) In which direction does a freely suspended magnet settle?

 Answer: The Earth itself behaves as a magnet which causes a freely suspended magnet (or magnetic needle) to point always in a particular direction: North and South.

*Q.3) Which metals are used for making magnets?

 Answer: Magnets are made from alloys of iron, cobalt and nickel. Nipermag, an alloy of iron, nickel, aluminium and titanium is used to make magnets. Alnico is a magnetic alloy of aluminium, nickel and cobalt.

 *Q.4) What are the characteristics of magnets?

 Answer: They seek the path of least resistance between opposite magnetic poles. In a single bar magnet as shown to the right, they attempt to form closed loops from pole to pole. They never cross one another. They all have the same strength. Their density decreases (they spread out) when they move from an area of higher permeability to an area of lower permeability. Their density decreases with increasing distance from the poles. They are considered to have direction as if flowing, though no actual movement occurs. They flow from the south pole to the north pole within a material and north pole to south pole in air.

Magnetism

 *Q.1) What do you mean by single touch magnetism?

 Answer: Place a steel bar AB, on a table. Take a bar magnet. Place its ‘N’ pole on the ‘A’ end of the steel bar and drag it towards the ‘B’ end. Lift the bar magnet and drag its ‘N’ pole from the end A to the end B of the steel bar again. Repeat this 15 to 20 times. Now take the steel bar near some iron filings and observe what happens. Hang the bar freely by a thread and observe. The steel bar will be seen to have developed magnetism. This method of magnetization is called the single touch method. The magnetism created by this method is of low strength and lasts for a short time.

Earth: A gigantic magne

**Q.2) What was the experiment done by scientist William Gilbert?

Answer: The scientist William Gilbert gave a scientific explanation, based on experiment, of the observation that a freely suspended magnet always settles in the north-south direction only. He gave a round shape to a naturally occurring magnetic rock. He suspended this spherical magnet so that it could turn freely and brought the north pole of a bar magnet near it. The south pole of the magnetic sphere was attracted towards it.

Magnetic needle

 *Q.1) Which direction will a magnetic needle show on the geographic north pole?

Answer: The north end of a magnet in a compass is attracted to the south magnetic pole, which lies close to the geographic north pole. Magnetic field lines outside of a permanent magnet always run from the north magnetic pole to the south magnetic pole.

 *Q.2) In any place, why does the magnetic needle of a compass not settle parallel to the ground but at an angle to it?

 Answer: A compass needle aligns itself with the Earth’s 3-dimensional magnetic field. Close to the equator this will be pretty much parallel to the ground but as to get closer to either the north or south magnetic poles the needle begins to dip. The amount that the needle dips is known as dip angle or angle of inclination. Magnetic field

**Q.1) What do you mean by magnetic lines force?

 Answer: The British researcher Michael Faraday named the lines, going from one end of the bar magnet to the other, ‘magnetic lines of force’.

 **Q.2) What is magnetic field?

Answer: The region around a magnet where the magnetic force acts on an object is called a magnetic field. The magnetic field around a magnet can be shown by means of magnetic lines of force.

Properties of magnetic lines of force

 **Q.1) What are the properties of magnetic field proposed by Michael Faraday?

Answer: While proposing the concept of lines of force, Michael Faraday argued that, if all observed effects are to be explained satisfactorily, then the lines of force must have certain properties. Properties of magnetic field Magnetic lines of force are imaginary connecting lines and Faraday introduced the concept of lines of force in order to explain magnetic  attraction and repulsion. Magnetic lines of force always run from the north pole to the south pole. The south pole may be of the same magnet or a different one. Magnetic lines of force are in a state of tension like a stretched spring. Magnetic lines of force repel each other. Magnetic lines of force do not intersect each other. The number of the magnetic lines force at a particular point determines the strength of the magnetic field there.

Penetrating ability of the magnetic field

 **Q.1) How can we measure penetrating ability of the magnet?

Answer: When we place a cardboard over the pins and then the magnet or drop some pins in the water of the water bottle and move the magnet above them the pins will stick to the cardboard and the bottle respectively. From the above observations, we see that a magnetic field can pass through a cardboard, a bottle or water. However, in each case, the intensity of the magnetic field is found to decrease

Metal detectors

 **Q.1) What are metal detectors? What are the uses?

Answer: The function of the metal detectors is based on electromagnets. Metal detectors are used in very important places like an airport, bus station, certain temples and buildings. They are used for inspection of persons entering these places. Metal detectors are used to detect very precious articles and also in the food—processing industry to detect any iron/steel objects mixed unknowingly in foodstuff as these would be harmful to health. In geology, these machines are used to detect the presence and quantity of metals.