Electronics-Transformers Question and Answer
Electronics-Transformers Question and Answer
1. When does maximum power transfer happen from the source to the load?
- When the source resistance is greater than the load resistance
- When the source resistance is less than the load resistance
- When there is negligible source resistance
- When the source resistance equals the load resistance
2. A transformer is plugged into a 120 V rms source and has a primary current of 300 mA rms. The secondary is providing 18 V across a 10 omega.gif load. What is the efficiency of the transformer?
- 88%
- 90%
- 92%
- 95%
3. The coefficient of coupling between two coils is 0.45. The first coil has an inductance of 75 mH and the second coil has an inductance of 105 mH. What is the mutual inductance between the coils?
- 3.54 mH
- 7.88 mH
- 39.9 mH
- 189.3 mH
4. Increasing the number of turns of wire on the secondary of a transformer will
- increase the secondary current
- decrease the secondary current
- have no effect on the secondary current
- increase the primary current
5. What is the turns ratio of the transformer needed to match a 1 komega.gif source resistance to a 160 omega.gif load?
- 2.5:1
- 0.4:1
- 6.25:1
- 16:1
6. The transformer turns ratio determines
- the ratio of primary and secondary voltages
- the ratio of primary and secondary currents
- the reflected impedance
- all of the above
7. Mutual induction is dependent on
- winding ratios
- output polarities
- dc voltage levels
- current changes
8. A special transformer used to convert unbalanced signals to balanced signals is the
- balun
- autotransformer
- center-tapped transformer
- step-across transformer
9. If the primary power of an ideal transformer having a 2:1 voltage ratio is 100 W, the secondary power is
- 100 W
- 50 W
- 75 W
- 200 W
10. A transformer has
- primary and secondary windings, both of which are considered inputs
- primary and secondary windings, both of which are considered outputs
- a primary winding used as an output and a secondary winding used as an input
- a primary winding used as an input and a secondary winding used as an output