Electronics Information – Test 1

The amount of power wasted in heat is a function of efficiency. Any power that is not useful, such as signal power, is wasted in heat. In order to determine the amount of wasted power, the total input power must first be determined by using the power formula(see Reference Sheet):P = IE

Once the total input power is found, subtract the useful power from it. What is left is the power wasted in heat.

P = IE = 0.1 * 48 = 4.8 W

4.8 W – 1.5 W = 3.3 W of wasted power

A communications system consists of a source, a medium and a sink (also referred to as a load or receiver). Efficient transfer of signal power depends on matching the impedance of each of these system components. When an impedance mismatch is present, the source “sees” a reactive load (refer to Question 21 discussion). When this occurs, I and Eare out of phase. Under these conditions, not all the signal energy is transferred to the receiver. The energy not transferred must go somewhere, so it returns to the source. This is referred to as reflected energy, commonly called “echo.” In order to reduce the level of reflected energy, it is important to match the impedance of the medium and the sink tothe source.

When values are in decibels, simply add the gains and subtract the losses from theoriginal level to determine the expected power level.

-10 dBm – 2 dB + 30 dB –3 dB + 20 dB – 5dB = 30 dBm

AC periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC), which flows only in one direction.

The frequency of a signal is the number of times it goes through a complete cycle of 360°in one second. A 1000-Hz signal completes 1000 cycles in one second. The period of a signal is the length of time it takes to complete one cycle, and a 1000-Hz signal has a period of 0.001 seconds (1/1000 of a second). As the frequency goes higher, the period becomes shorter: 10,000 Hz has a period of 0.0001 seconds (1/10,000 of a second).Therefore, frequency and period are inversely related. All other answer choices are independent of frequency.

Direct current may flow through a conductor such as a wire, as well as  semiconductors, insulators, or a vacuum as in electron or ion beams.

A diode typically conducts current in one direction, has low resistance in one direction, and high resistance in the other.

In solid state component symbols, the arrow always points toward the N-type material. APNP transistor will have the arrow pointing at the base as in Figure 2D.

Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points.

Other uses include bias active elements and terminate transmission lines. High-power resistors may be used as part of motor controls, in power distribution systems, or as test loads for generators.

There is a simple relationship between peak voltage and rms voltage of a sine wave. Therms voltage is 0.707 * peak voltage (see Reference Sheet). When the rms voltage (alsocalled effective voltage) is known, solve for peak voltage by dividing the rms voltage by0.707.

V_peak = rms/0.707 = 220/0.707 = 311 V