155. For heating of plywood, the frequency shoiuld be
A. 100 Hz
B. 1000 Hz
C. 10-20 kHz
D. 1-2 MHz

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156. High frequency for induction heating can be generated by
A. motor generator set
B. spark gap oscillator
C. vacuum tube oscillator
D. All of these

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157. Steel rails are welded by
A. Argon arc welding
B. Thermit welding
C. Gas welding
D. Resistance welding

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158. Quantities having the unit "lux" is
A. Utilization factor
B. Luminous flux
C. Luminous intensity
D. Illumination

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159. Which of the following statements about illumination is true?
A. If the distance from the source doubles, the illumination becomes half
B. If the distance from the source doubles, the illumination reduces to one fourth
C. The greater the illumination, the better one sees
D. The finer the work, the less the required illumination

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160. The highest illumination is required
A. for office work
B. for mounting of wrist watches
C. for sorting work in the stores
D. for painting work.

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161. Which of the following comparisons between the filament lamp and the fluorescent lamp is correct?
A. The flurescent lamp has a higher dazzle
B. The fluorescent lamp produces shrper shadows
C. The fluorescent lamp produces greater brightness
D. The average life of the fluorescent lamp is five to seven times higher.

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