Important conceptual science question for CDS
As you know, the general studies part in the CDS examination plays a very important role. For your knowledge, the science part covers almost 23% of the total number of questions in the general studies examination. Proper revision of the concepts and formulae of science especially physics is a must to do before going for the CDS exam. This is because most of the questions in physics are concept based.
So here we are with some of the most important concepts of physics for NDA/CDS exam:
- When we shake the branch of a mango tree, the mangoes fall down.
- A man jumping from a moving vehicle falls down.
- We use a stick to remove dust from a carpet.
These all are the applications of the law of inertia (our body stays at rest or continues the motion unless an external force is applied on it).
- A jet plane moves on the principle of Newton’s third law of motion. The exhaust gases come out from the nozzle, the plane moves forward in the reaction. To know more about how does a plane flies, click here
- If someone left on a frictionless floor wishes to get out of it, he can do so by blowing air out of his mouth. This is due to the law of conservation of momentum. Furthermore, rocket also works on the principle of conservation of momentum.
Practical applications of thermal expansion of substances:
- A soft glass breaks when hot tea poured into it.
- The hand of a pendulum runs faster in winters because in summers, its length increases due to thermal expansion.
- A tightly fitted cork can be removed from the glass bottle by heating its mouth easily.
- Water droplet from spherical shape due to the surface tension.
- A solid ball of iron sinks in water but floats over Mercury because the density of iron is greater than that of water but lesser than that of Mercury.
- The speed of a fluid increases in narrower pipe.
- The value of gravity ‘g’ decreases with the increase in rotation speed. That is why the value of gravity is maximum at poles and minimum at equator.
- A person is able to rotate with a large angular speed buy folding his arms because this decreases the moment of inertia.
- The specific heat of water is maximum.
- The density of water is maximum at 4°C.
- Radiation pyrometer (used to measure the temperature/radiation of the Sun) can’t be used to measure temperature below 800°C. This is because below that temperature, there is no significant emission of radiation.
- Cool air flows downwards. This is the reason that the cooling unit is at the top in refrigerators.
- Steel is more elastic than rubber.
- A fountain pen leaks in an aeroplane because the atmospheric pressure decreases with the rise in altitude.
- It is easier to swim in the sea than in a river because the seawater is saline i.e. has more density.
- To prevent loss of water from the soil, the farmers make the soil loose using a plough. This is due to the capillary action by virtue of which the root hairs of plants absorb water from soil.
- We are able to see the lightning before the lightning sound because the speed of light is greater that that of sound in air.
These are just few of the questions based on real life events and one who has already appeared for NDA/CDS knows very well, the importance of such questions.