1. Describe a simple experiment to show
that light travels in a straight line.
2. List three properties of a shadow.
3. In what ways water is so important for
our body?
4. a. Why are magnetic keepers used to
store magnets?
b. Given a bar magnet, describe the method
you will use to magnetize an iron nail.
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1. Take three cardboards A, B and C. Take a pin and make a small hole at the centre of the three cardboards. Mount them vertically such that the holes are falling perfectly in a line. Place a lighted candle near one of the cardboards (say A). Look at the candle flame from the other side of the cardboard C. The candle flame is clearly seen. Now slightly displace one of the cardboards (say B) so that the holes no longer remain in a straight line. Now again look at the candle flame from the other side of the cardboard C. We will notice that the candle flame is not visible now. This proves that light travels in a straight line and the holes in the cardboard A, B and C are not in a straight line.
2. A shadow has the following properties:
i) The colour of the shadow is always dark, that is, black or grey, irrespective of the colour of the object.
ii) A shadow shows only the outline and the shape of the object, and not its detail.
iii) A shadow cannot be obtained without a screen.
3. The functions of water in our body are:
(i) Water is the main constituent of blood which contributes to the transport of nutrients to the cells
(ii) Helps our body to absorb nutrients from the food
(iii) Essential for cells to function properly
(iv) Helps in body temperature regulation
(v) Removal of waste from the body in the form of urine and sweat.
4. a. A magnetic keeper is a piece of wood or soft iron which is used in storing magnets because bar magnets get demagnetised when the poles are left free for a long time. In order to preserve the magnetism of the magnets, a keeper is kept across a pair of bar magnets with unlike poles beside each other.
b. An iron nail can be magnetised by a bar magnet by a process of stroking. In this method, one pole of a bar magnet is used to stroke the iron nail held firmly on a surface. Stroke the iron nail from one end to the other and after reaching the other end, lift the magnet and repeat the process by bringing it back to the first end again. After about 30 strokes, we will observe that the iron nail has become a magnet when suspended freely. If the iron nail has been stroked by the north pole at the first end, that end becomes the north pole while the other end becomes the south pole.
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