It is much easier to build large reflectors than large refractors
Indicate whether the statement is true or false
TRUE
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A spaceship, moving away from the Earth at a speed of 0.9c, fires a light beam backward. An observer on Earth would see the light arriving at a speed of
A. 0.1c. B. 1.9c. C. more than 0.1c but less than c. D. c. E. more than c but less than 1.9c.
An electric device, which heats water by immersing a resistance wire in the water, generates 50 cal of heat per second when an electric potential difference of 12 V is placed across its leads. What is the resistance of the heater wire? (Note: 1 cal = 4.186 J)
a. 0.94 ? b. 0.81 ? c. 0.58 ? d. 0.69 ? e. 1.5 ?
A cold front traveling at an average speed of 35 km/h eastward is 280 km due west of you. Approximately how long will it be before your location experiences a sudden temperature drop?
When a 60 Hz sinusoidal voltage is applied to the input of a half-wave rectifier, the output frequency is
a. 30 Hz. b. 60 Hz. c. 120 Hz. d. 90 Hz.