Physics
Which one of the following is not a property of electromagnetic waves?

Electromagnetic waves do not require a medium to propagate.
Electromagnetic waves are transverse waves
Electromagnetic waves do not show interference and diffraction.
Oscillating electric field and magnetic field are perpendicular to each other.

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Physics
When a piece of pure silicon is doped with aluminium, then

The resistivity of the doped silicon piece will increase
The conductivity of the doped silicon piece will remain the same
The doped silicon piece will become p-type
The doped silicon piece will become n-type

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