Thin Lenses: A drawing is placed 40 cm in front of a thin lens. If a virtual image forms at a distance of 50 cm from the lens, on the same side as the drawing, what is the focal length of the lens?
A. -45 cm
B. 75 cm
C. 90 cm
D. 200 cm
E. +45 cm
Answer: D
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Comparing the electrostatic force and the gravitational force we can say that
A. both have the same dependence on distance, the electrostatic force can be either attractive or repulsive while the gravitational force is only attractive, and the electrostatic force is stronger. B. the electrostatic force falls off more rapidly with distance, the electrostatic force can be either attractive or repulsive while gravitation is only attractive, and the electrostatic force is stronger. C. both have the same dependence on distance, both involve attraction and repulsion, but the gravitational force is stronger. D. both have the same dependence on distance, the electrostatic force can be either attractive or repulsive while the gravitational force is only repulsive, and the electrostatic force is weaker. E. both have the same dependence on distance, both involve attraction and repulsion, but the electrostatic force is stronger.
When 10 kcal of heat is added to 2.0 kg of a substance, its temperature increases 20 C°. What is the specific heat of the substance?
Mars appears red in color because of refraction of light by its atmosphere, much like the color of the totally eclipsed Moon
Indicate whether the statement is true or false
An engine delivers 40.0 J of work while it takes in energy from a 400 K thermal source. If the engine discharges energy into a thermal reservoir at 200 K, then what is the least amount of heat needed to run the engine?
A. 55.0 J B. 65.0 J C. 80.0 J D. 110 J