Light Energy — PHYSICS STD 7 — Question

Given below statement is incorrect. Write the correct statement :
In SI system, unit of speed is Kmh^-1.

State one application of thermal expansion of liquids.

Why does a piece of paper appear white in sunlight ? How would you expect it to appear when viewed in red light?

What is the time period of a particle that is vibrating at a frequency of 10 Hz?

Explain the following :
Why do we wear white or light coloured clothes in summer?

Write the audible range of frequency for the normal human ear.

Given below statement is incorrect. Write the correct statement :
The fixed temperature at which a solid changes into liquid state with the release of heat energy is called melting point.

State whether light slows down or speeds up in the following cases :
Light going from glass to water.

Given below statement is incorrect. Write the correct statement :
The metallic wires contract during summer and can break.

Given below statement is incorrect. Write the correct statement :
During photosynthesis by plants, the heat energy changes to light energy.