* Gas constant is expressed in units of energy per temperature increment per mole 

* According to ideal gas law, PV=nRT; 

Where P= Absolute pressure, V=Volume of gas, n=Amount of gas, m=Mass contained in V, T= Thermodynamic Temperature, R=Molar weight specific gas constant 

→ R=(PV)/(nT)=Joule/(mole*Kelvin)=J/(K.mol)

The power of a lens is defined as the reciprocal of its focal length in meters, or D = 1/f, where D is the power in dioptres and f is the focal length in meters. 

Given power is +2 dioptres 

So from above formula 

D = 1/f 

+2 = 1/f 

f = 1/2 = 0.5m or 50cm.

A hydrometer or areometer is an instrument that measures the specific gravity (relative density) of liquids—the ratio of the density of the liquid to the density of water. Lctometer is used to test the purity of milk.So, lactometer is wrong here.

Sphygmomanometer is an instrument for measuring blood pressure. It consists an inflatable rubber cuff which is applied to the arm and connected to a column of mercury next to a graduated scale, enabling the determination of systolic and diastolic blood pressure by increasing and gradually releasing the pressure in the cuff.

• The weight of an object on the Earth's surface is the downwards force on that object, given by Newton's second law of motion, or F = ma (force = mass ×acceleration).
• Gravitational acceleration contributes to the total acceleration, but other factors, such as the rotation of the Earth, also contribute, and, therefore, affect the weight of the object.
• As the gravity is slightly higher at the poles, the weight is more as compared to anywhere else.

A wind rose is a graphic tool used by meteorologists to give a succinct view of how wind speed and direction are typically distributed at a particular location. It shows wind turbulence.

Concave mirror: The reflecting surface is towards centre of sphere while outer surface is polished. 
Applications: 

a) These mirrors are used in ophthalmoscope, which reflects light from retina of the eye of the patient. 

b) These are used in search lights 

c) These are used in mirrors that are used in saloons.

• Of all planet, only venus and mercury have no known natural satellites.


• A total of 139 moons or natural satellites, can be found in vast solar system.

Pure water is always a bad conductor of electricity. This is because the electrons in the water molecules are not in the conduction band at the room temperature and at a higher temperature, the water is not fit for conducting as the state changes. However, the water which we use in our day - to - day life has many dissolved ions in it which get dissociated and are ready to conduct electricity. Also, the water in our homes contains these ionic and covalent salts which can conduct the electricity. Hence when we, with wet hands, touch the wire or SWITCH boards often get a shock. 

• Bats use echolocation to navigate and find food in the dark.
• To echolocate, bats send out sound waves from their mouth or nose. When the sound waves hit an object they produce echoes.