When a liquid or gas is heated it, it expands on heating, i.e its length, area and volume increases. Hence, its density decreases.

The SI unit of density is kgm^-3 .

Reflection from a rough surface is called diffuse reflection.

Umbra is the region of total darkness as no ray of light enters this region.

A dry cell converts chemical energy into electrical energy.

A closed path in which electric current flows is called an electric circuit.

Butter paper is a translucent object. Translucent object transmits only partial light through it.

Pinhole camera works on the principle that light travels in a straight line.

Ampere is the unit of current and it is not required for an electric circuit.

212^oF is the upper fixed point of Fahrenheit scale.

Lateral inversion is the phenomenon due to which left hand side of an object appears as the right hand side and vice-versa.

Light energy is an invisible energy which causes the sensation of vision.

Iodine sublimes and directly changes into gas when heated.

Weight of a body changes with place.

One complete to and fro motion of a pendulum is called oscillation.

The density of water is maximum at 4^oC. This is known as anomalous expansion of water.

Sound cannot travel in vacuum.

Pitch of a sound depends upon frequency.

Sound is produced by a vibrating body.

The maximum displacement of the bob of a pendulum from its mean position is called amplitude.

Concave mirror is used in reflector-type solar cooker to converge sun rays towards the vessel to be heated.

The property by virtue of which solids increase in size on heating is called thermal expansion.

Those physical quantities that possess only magnitude but no specific direction are called scalar quantities. Distance is a scalar quantity.

The shadow of the bird cannot be formed because the extended source of light (the Sun) is very large as compared to the opaque body (the bird). The bird is very small as compared to the diameter of the Sun. The umbra formed by the bird is so small that it finishes in the air while the penumbra formed is very light and faint, i.e. hardly visible.

The length of the pendulum increases during summers due to which the time period increases. So, the pendulum takes a longer time to complete one oscillation. Therefore, a pendulum clock loses time during summers.

Plane mirror is used in a periscope. Periscope works using the laws of reflection. It is used in submarines.