☰ अधिक माहितीसाठी येथे क्लीक करा

#### Question 1:

How will you do this?
(a) Determine whether a material is magnetic or non-magnetic.
(b) Explain that a magnet has a certain magnetic field.
(c) Find the north pole of a magnet.

(a) If a material sticks to a magnet, then it is a magnetic material otherwise it is a non-magnetic material.

(b) A magnet has a certain magnetic field which can be demonstrated using the below activity.
Take a drawing cardboard and sprinkle some iron filings on it. Notice the position of the iron filings as a whole. Now, take a bar magnet and slowly bring it below the cardboard. You will observe that the iron filings tend to attract towards the magnet and align themselves as shown.

It represents that the magnet exerts a force around its body with a stronger force near the two poles. Also, this regular pattern of the iron filings on the board represents the lines of magnetic field. Thus, a magnet has a certain magnetic field which can be represented by curved lines around a magnet.

(c) Tie a thread to the centre of a magnet and hang it from a stand as shown. Wait till the magnet settles itself.
The pole that point towards the geographic north is the North-Pole of the magnet.

#### Question 2:

Which magnet will you use?
(a) Iron is to be separated from trash.
(b) You are lost in a forest.
(c) A window shutter opens and shuts continuously in the wind.

(a) Electromagnet can be used to separate iron from trash.

(b) Bar magnet or loadstone can be used to find the direction in the forest. This is because a bar magnet, when suspended freely, always rests in north-south direction.

(c) Permanent magnet can be used to stop the continuous shuttering of the window in the wind.

#### Question 3:

Fill in the blanks with the appropriate word.
(a) If a bar magnet is hung by a thread tied at its centre, its north pole becomes steady in the direction of the ................ Pole of the earth.
(South, north, east, west)
(b) If a bar magnet is cut into equal pieces by cutting it at right angles to its axis at two places, ........... bar magnets are formed, and a total of ................ poles are formed.
(6,3,2)
(c) There is repulsion between the .......... poles of a magnet, and attraction between its ............ poles.
(opposite, like.)
(d) When magnetic material is taken close to a magnet, the material acquires ............... .
(permanent magnetism, induced magnetism)
(e) If a magnet attracts a piece of metal, that piece must be made of ............. .
(any other metal but iron, magnetic material or iron, non-magnetic material)
(f) A magnet remains steady in a .............. direction.
(east-west, north-south)

(a) If a bar magnet is hung by a thread tied at its centre, its north pole becomes steady in the direction of the north Pole of the earth.
(b) If a bar magnet is cut into equal pieces by cutting it at right angles to its axis at two places, 3 bar magnets are formed, and a total of 6 poles are formed.
(c) There is repulsion between the like poles of a magnet, and attraction between its oppositepoles.
(d) When magnetic material is taken close to a magnet, the material acquires induced magnetism.
(e) If a magnet attracts a piece of metal, that piece must be made of magnetic material or iron.
(f) A magnet remains steady in a north-south direction.

#### Question 4:

(a) How is an electromagnet made?
(b) Write the properties of a magnet.
(c) What are the practical uses of a magnet?

(a) For the construction of an electromagnet, we require an iron nail, a long insulated copper wire, a battery and a switch.
The long insulated copper wire is first wound on the iron nail. Then the two free ends of the wire is connected to the battery and the switch as shown. Now, when the switch is turned on, current flows through the circuit. Due to this flow of current, the insulated copper wire  and iron nail acts as an electromagnet. Now, if iron pins are brought close to this set-up, they stick to the iron nail.
As soon as the current stops flowing in the circuit, the iron nail loses magnetism and the pins fall off.

(b) Properties of a magnet are following:

• A magnet has two poles known as North-Pole and South-Pole.
• A magnet, when suspended freely, always rests in north-south direction.
• A magnet has an attractive properties i.e. it always attracts magnetic materials towards it.
• Like poles of magnets repel each other whereas unlike poles attract each other.
• The two poles of a magnet are inseparable. It means that when a magnet is cut into two parts, two independent magnets are formed.
• Magnetic force of a magnet is concentrated at its two poles.

(c) Magnets have very wide range of uses:
• Magnetic compass: With the help of a magnetic compass, you can know the directions at a particular place. The red end of the needle indicates the North direction.
• Magnets in daily life: Magnets are used in refrigerator doors, as pin holders, in screwdrivers, etc.
• Magnet in junkyard: In the junkyard, you will see that a large magnet is attached at the bottom of the arm of a crane. The arm moves over a heap of junk and the magnet collects objects made of iron. The magnet used in a junkyard crane is not a natural or a permanent magnet. It is a temporary magnet, which is called an electromagnet.
• Magnet in electrical appliances: Magnets are also used in many electrical appliances such as electric bells, telephone, telegraph, radio, loudspeaker, fans, electrical motors, electric generator, etc.
• Magnet for security: While going to some important places like temples, buildings, airport etc. you will see equipments for inspection of people entering these places. These equipments uses magnets and are known as Metal detectors. These metal detectors are also used in food-processing industry to detect any unwanted iron/steel objects mixed unknowingly in food stuff.
Std 6 th Science- 15. Fun with Magnets Reviewed by Amol Uge on January 08, 2019 Rating: 5