Class 10 notes

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Introduction to Light – Reflection & Refraction Light: Definition Light is a form of energy that enables us to see things. Light starts from a source and bounces off objects which are perceived by our eyes and our brain processes this signal, which eventually enables us to see.

  Physical and chemical changes Chemical change - one or more new substances with new physical and chemical properties are formed. Example:  F e ( s )   +   C u S O 4 ( a q ) → F e S O 4 ( a q ) + C u ( s )                                     (Blue)                      (Green)            Here, when copper sulphate reacts with iron, two new substances, i.e., ferrous sulphate and copper are formed. Physical change - change in colour or state occurs but no new substance is formed. Example: Water changes to steam on boiling but no new substance is formed(Even though steam and water look different when they are made to react with a piece of Na, they react the same way and give the exact same products). This involves only change in state (liquid to vapour).  Observations that help determine a ch...