Kaleidoscope is an instrument used to make numerous beautiful patterns.
To make a kaleidoscope get three rectangular mirror strips. Join them together to from a prism. Close one end of tube by cardboard disc having a hole in the centre. Paste a piece of transparent plastic sheet at the other end. Put several small pieces of coloured glass bangles. Allow enough space for the coloured pieces to move around.
Numerous beautiful patterns will be formed. It is used by designers of wall papers and fabrics and artists to get new ideas for new patterns.

Outside the house:
(i) Open vehicles, such as motorbikes, tractors, construction machinery, and open cars are not safe.
(ii) Open fields, tall trees, shelters in park, elevated place do not protect us from lightning strokes.
(iii) Carrying an umbrella is also not safe.
(iv) Stay away from poles or other metal objects.
Inside the house:
(i) During a thunderstorm contact with telephone cords, electrical wires and metal pipes should be avoided.
(ii) It is safe to use mobile phone.
(iii) Bathing should be avoided.
(iv) Electrical appliances like computers, TVs etc. should be unplugged. Electrical lights can remain on.

Given, number of oscillations = 10
Time taken = 20 s
As, we know that the number of oscillations per second is frequency.
\(\therefore frequency=\frac { Number\ of\ oscillations }{ Time\ taken } =\frac { 10 }{ 20 } =0.5Hz\\ \therefore time\ period=\frac { 1 }{ Frequency } =\frac { 1 }{ 0.5 } =2s\)

No, scientists have tried lots of different ways of predicting earthquake but none have been successful so far. They have a pretty good idea of where an earthquake is most likely to hit but they still cannot tell exactly when it will happen.

When blacksmith hammers a hot piece of iron, the force due to hammering can change the shape of the piece of iron. In other words, we can say that force applied through the hammer by the blacksmith can mould the hot piece of iron into any kind of tool.

At the junction of the optic nerve and the retina, there are no rods and cones. Hence, no vision is possible at the spot. This spot is called blind spot.

Sound frequencies higher than 20,000 Hz are called ultrasound. It is used as diagnostic tool in medical science. It is also used to relieve pains in joints, muscles. It is used to detect flaws in metal and structures, and to test the thickness of various parts.

On being struck by lightning, victim carries no electrical charge. The death by lightning occurs due to cardiac arrest and stopped breathing. We can give first aid by performing CPR and mouth to mouth breathing.

When two equal forces act in opposite directions, the net force becomes zero.

Kaleidoscope is a device that is generally used by the designers of wallpapers and fabrics.

Lightning enables ozone to be formed from oxygen.

Sound wave cannot propagate in vacuum.

Mass of an object remains constant at all the places, so mass of astronaut will not change. Weight of an object depends upon the gravity, at the moon gravity is lesser than earth, so weight of astronaut will decrease.

We do not feel atmospheric pressure on our body. It is due to the pressure inside our body is nearly equal to atmospheric pressure.

Due to broad feet of camels, they usually exert less pressure in the sand, so camels sinks less in the sand.

In order to protect us from electrical shock due to leakage of electric current, the earthing is provided in the building.

X sound is ultrasonic sound, Y sound is infrasonic sound and Z sound is audible sound.

(a) Number of mirrors = 3
(b) Positions of the mirrors are as shown in figure.
(c) Mirrors should be placed at 45° w.r.t. the incident light. So, that ray can move forward.
(d) Direction of rays is shown in figure.
(e) He will not be able to see the objects if any of the mirrors is removed since he will not get the rays after that removed mirror.