Physics

Humidity is the amount of water vapour in the air. The vapour content of air is measured with devices known as hygrometers. The measurements are usually expressed as specific humidity or percent relative humidity.

Electron microscope works on the principle of Wave Nature of electrons. Electron microscopes use an electron beam instead of visible light and an electron detector instead of our eyes. An electron beam allows us to see at very small scales because electrons can also behave as light due to its wave nature.

Increasing the focal length of objective increases the magnifying power of the telescope. Increasing the focal length of the eye-piece decrease the magnifying power of telescope.

Rate at which velocity changes over time is called acceleration.

A single solar cell can produce only a small amount of electricity. In those cases where more electrical power is needed, a large number of solar cells are joined in series. This group of solar cells is called a ‘solar cell panel’. Thus, a solar cell panel consists of a large number of solar cells joined together in a definite pattern.

When the brush is taken out of water, the hairs cling together due to surface tension. This happens because the free surface of water tries to acquire a minimum surface area.

When a bullet is fired from a gun, the gun exerts a force on the bullet in the forward direction. This is force is called as the action force. The bullet also exerts an equal and opposite force on the gun in the backward direction. Therefore a gun recoils when a bullet is fired from it.

A single fixed pulley is used to draw a bucket of water from a well. It is easy to draw from a well using a pulley because it helps in changing the direction of the force applied. This, in turn, makes it easy to move the object. In this case, the pulley helps in lifting the bucket full of water upwards.

Wilhelm Roentgen discovered X-ray.