Which of the two signs shown below would indicate the greatest danger?
B indicates grave danger. The danger to the body, and even to life, comes from electrical current in the body, which could occur if you accidentally make contact with a large potential difference across parts of your body.
The effect of a high resistance is to limit current in a circuit if a voltage source is present; it is not dangerous at all.
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An X-ray technician takes an average of ten X-rays per day and receives 2.5 mrad per X-ray. What is the total dose the technician receives in 250 working days?
A) 2.50 rem B) 5.00 rem C) 6.25 rem D) 7.75 rem E) 12.5 rem
A thermocouple (0.8-mm-OD) is located horizontally in a large enclosure whose walls are at 37°C. The enclosure is filled with a transparent quiescent gas that has the same properties as air. The electromotive force (emf) of the thermocouple indicates a temperature of 230°C. Estimate the true gas temperature if the emissivity of the thermocouple is 0.8.
GIVEN
• Horizontal thermocouple in a large enclosure
• Thermocouple outside diameter (D) = 0.8 mm = 0.0008 m
• Enclosure wall temperature (Te) = 37°C = 310 K
• Gas is enclosure is quiescent and has the same properties as air
• Thermocouple reading (Ttc) = 230°C = 503 K
• Thermocouple emissivity (?) = 0.8
FIND
• True gas temperature (T?)
ASSUMPTIONS
• Enclosure behaves as a black body
• Conduction along the thermocouple out of the enclosure is negligible
SKETCH
PROPERTIES AND CONSTANTS
The Stephan-Boltzmann Constant (?) = 5.67 ?10–8 W/(m2 K4).
If a newly discovered planet has four times the mass of Earth, but it still has the same surface gravity as Earth, how big must this new planet be?
A. half the size of Earth B. the same size as Earth C. twice as large as Earth D. four times as large as Earth E. one fourth of the size of Earth
What are the two basic conditions necessary for laser action?
What will be an ideal response?