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

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

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Physics
A standing wave occurs when

The amplitude of a wave exceeds its wavelength
Two waves overlap
The speed of the wave is zero or near zero
A wave reflects upon itself

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Physics
Solar eclipse will take place when

the earth is between the moon and the sun
the moon is between the sun and the earth
the sun is between the moon and the earth
the moon does not lie on the line joining the sun and the earth

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