Which describes increasing the efficiency of an energy resource? a using biomass instead of coal b switching from coal to solar c turning off the lights when leaving a room d making cars that get better gas mileage

Diamond will scratch quartz. true or false

Athin electrical heater is inserted between a long circular rod and a concentric tube with inner and outer radii of 20 and 40 mm. the rod (a) has a thermal conductivity of ka = 0.15 w/(m*k), while the tube (b) has a thermal conductivity of kb = 0.8 w/(m*k) and its outer surface is subjected to convection with a fluid of temperature t= -15°c and heat transfer coefficient 60 w/(m2 *k). the thermal contact resistance between the cylinder surfaces and the heater is negligible. (a) determine the electrical power per unit length of the cylinders (w/m) that is required to maintain the outer surface of cylinder b at 15°c. (b) what is the temperature at the center of cylinder a?

A: all waves on the electromagnetic spectrum travel at the same speed in a vacuum. the speed of these waves in a vacuum is 3x108 m/s. as the wavelength of a wave doubles, how does the speed and frequency of the wave change?