Monthly Test, Physics 12 (December)

A capacitor is perfectly insulator for

• direct current

• alternating current

• AC and DC both

• none of these

The alternating voltage is given by 15Sin157t. The frequency of alternating voltage is--------Hz.

• 25

• 50

• 75

• 100

In a purely inductive AC circuit the current lags behind the voltage by --------degrees.

• 30

• 45

• 60

• 90

The mean value of sinusoidal emf over a cycle is-----

• 0

• 1

• 2

• none of these

The material with the biggest energy gap is called---------

• insulator

• conductor

• Semi conductor

• super conductor

Which one is semi conductor material-----

• Ga

• As

• Ge

• Al

In an insulating material-----

• the valence band is filled and conductor band is empty

• the valence band is empty and the conductor band is filled

• both the conductor and valence band is empty

• both the conductor and valence band are filled

Which superconductor was discovered in 1986-----

• mercury

• porcelain

• ceramic

• coil

A resistor is connected to an AC power supply on this circuit current------

• leads the voltage by 90 degree

• less the voltage by 90 degree

• is in phase with the voltage

• none of these

If the frequency of a voltage across an inductor is doubled,the inductive reactance of that inductor-----

• increase to 4 times

• increase to twice

• decreases to one half

• decreases to one fourth