When you put an object in light, a shadow is sometimes formed. Which of these is the reason why shadows occur? A) Shadows are formed because of reflection of light from the object. B) Shadows are formed because some light is blocked by the object.
C) Shadows come out of a person or an object when light shines on them.
D) Shadows are always there but we see them only when light shines on them.

Acoal-fired plant generates 600 mw of electric power. the plant uses 4.8 x 10^6 kg of coal each day, and the heat of combustion of coal is 3.3x 10^7 j/kg. the steam that drives the turbines is at a temperature of 300° c, and the exhaust water is at 37° c. (a) what is the overall efficiency of the plant for generating electric power? (b) how much thermal energy is exhausted each day? (c) what is the change in entropy of the universe for this heat engine? (d) using the same heat reservoirs, what is the maximum possible (carnot) efficiency for a heat engine?

Glass has a hardness that is in the middle of the hardness scale. what is the hardness of glass?

State the below theories and give the name of the writer of the theory 1. wave theory 2. quantum theory 3. corpuscular theory 4. electromagnetic theory