MCQ
When $NPN$ transistor is used as an amplifier
- ✓Electrons move from base to collector
- BHoles move from emitter to base
- CElectrons move from collector to base
- DHoles move from base to emitter
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| List $I$ | List $II$ |
| $A$ Microwaves | $I$ Radio active decay of the nucleus |
| $B$ Gamma rays | $II$ Rapid acceleration and deceleration of electron in aerials |
| $C$ Radio waves | $III$ Inner shell electrons |
| $D$ $X$-rays | $IV$ Klystron valve |
Choose the correct answer from the options given below

Assertion $A$: The phase difference of two light waves change if they travel through different media having same thickness, but different indices of refraction.
Reason $R:$ The wavelengths of waves are different in different media.
In the light of the above statements, choose the most appropriate answer from the options given below
