CBSE Class 12-science Physics Characteristics of EM Waves

• please resolve with good explanation
  
• which of the following does not travel in vaccum
  
• what is displacement current? why this concept was introduced?
• Please answer this.  What is meant by the term 'displacement current'? Briefly explain how this current is different from a conduction current.
• Why is the intensity of light is directly proportional to the square of amiplitude  
• pls explain
  
• Why light can travel in vacuum where as sound can not do so
• What is polarisation
• how are frequency and intencity of electromagnetic wave related?
• What is an electromagnetic wave?

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