# World Science and Technology – Exercise – 4

Exercise – 4

151. In the United States the television broadcast standard is…?

(a) PAL
(b) NTSC
(c) SECAM
(d) RGB

Explanation
Explanation : PAL and SECAM are standards used in other countries. RGB stands for red, green, and blue – the colors of light used to create an image in a color tv set and is often used as a format name for computer monitors. Let us discuss.
Discuss

152. Voltage is sometimes referred to as EMF, or Electromotive…?

(a) Field
(b) Factor
(c) Flash
(d) Force

Explanation
Explanation : The term EMF, or Electromotive Force, its use now in decline, is attributed to Italian physicist Alessandro Volta (1745-1827). Today we generally use the term “voltage” – can you guess why we call it that? Let us discuss.
Discuss

153. When measuring the characteristics of a small-signal amplifier, say for a radio receiver, one might be concerned with its “Noise…”?

(a) Fundamental
(b) Fall
(c) Force
(d) Figure

Explanation
Explanation : “Noise figure” is one critical parameter for determining the “quality” of a low-noise, small-signal, amplifier, and perhaps more importantly, the sensitivity of the overall receiver system. It is especially important for VHF (very high frequency) – and higher frequency – designs where most of the undesired “noise” (noise that masks or overpowers the desired signals) is generated internal to the electronics itself. In HF (high frequency) applications, atmospheric noise plays a much larger role in determining overall useful sensitivity, so a circuit’s “noise figure” is less important. Let us discuss.
Discuss

154. A given signal’s second harmonic is twice the given signal’s __________ frequency…?

(a) Fourier
(b) Foundation
(c) Fundamental
(d) Field

Explanation
Explanation : A given signal’s second harmonic is twice the given signal’s fundamental frequency. Harmonics are generated when there are non-linearities in an amplifier (there are always non-linearities). The worse the non-linearities, the more harmonics. A signal at 27.5 MHz (approximate frequency for US citizen’s band) would have a second harmonic at 55.0 MHz (on US channel 2!). Can you see why there might be problems? A CB operator might do well to place a low-pass filter on his radio. Let us discuss.
Discuss

155. “FET” is a type of transistor, Its full name is ________ Effect Transistor…?

(a) Field
(b) Factor
(c) Flash
(d) Force

Explanation
Explanation : The terminals of FETs are called gate, drain and source. You might be more familiar with bipolar junction transistors (BJTs), which have terminals called base, collector and emitter. FETs were conceptualized first, but BJTs were easier to produce and so developed sooner. Let us discuss.
Discuss