Electronic Devices And Circuits - Study Mode

[#66] What is the necessary a.c. input power from the transformer secondary used in a half wave rectifier to deliver 500 W of d.c. power to the load?
Correct Answer

(A) 1232 W

Explanation

Solution: Understanding Half-Wave Rectifiers: A half-wave rectifier only uses one-half of the input AC cycle to produce DC power. It essentially "chooses" the positive (or negative) part of the wave and discards the rest. Power Loss: Because it ignores half the input AC cycle, a significant portion of the input power is wasted as heat. This means the AC input power needed is much greater than the DC output power. Calculating Input Power: To find the AC input power, we need to consider this loss. For an ideal half-wave rectifier (no losses other than discarding half the wave), the relationship is approximately: AC Input Power ≈ 2 x DC Output Power Applying to the Problem: The question states that the DC output power is 500W. Therefore: AC Input Power ≈ 2 * 500W = 1000W Why the options are different: The options provided are slightly different from our simple calculation because real-world rectifiers have additional losses (like those in the transformer and diodes). However, our calculation gives us an approximation to help us pick the most likely answer. Considering the losses, the closest option is 1232 W. Therefore, the best option is A.

[#67] A thermistor is a
Correct Answer

(C) Miniature resistance

Explanation

Solution: A thermistor is a special kind of resistor. Resistors are electronic components that resist the flow of electricity. A thermistor is unique because its resistance changes depending on its temperature. Think of it like this: a normal resistor always has the same resistance, no matter how hot or cold it is. But a thermistor's resistance goes up or down as its temperature changes. Option A is incorrect because a thermocouple measures temperature using the difference in voltage between two dissimilar metals. Option B is incorrect because a thermometer usually measures temperature using the expansion of a liquid or metal. Option C is the correct answer because a thermistor is basically a small resistor that's very sensitive to heat. Its resistance changes noticeably with temperature changes. Option D is incorrect because thermistors are not explosive. They are passive components.

[#68] In an ideal diode there is no breakdown, no __________ current, and no forward __________ drop.
Correct Answer

(A) Reverse, voltage

[#69] The dynamic resistance of a forward biased p-n diode
Correct Answer

(A) Varies inversely with current

[#70] Each cell of a static Random Access memory contains
Correct Answer

(A) 6 MOS transistor